<?xml version="1.0" encoding="UTF-8"?>
<chapter xml:id="orm"
    xmlns="http://docbook.org/ns/docbook" version="5.0"
    xmlns:xl="http://www.w3.org/1999/xlink"
    xmlns:xi="http://www.w3.org/2001/XInclude"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://docbook.org/ns/docbook http://www.docbook.org/xml/5.0/xsd/docbook.xsd
        http://www.w3.org/1999/xlink http://www.docbook.org/xml/5.0/xsd/xlink.xsd">
  <title>Object Relational Mapping (ORM) Data Access</title>

  <section xml:id="orm-introduction">
    <title>Introduction to ORM with Spring</title>

    <para>The Spring Framework supports integration
    with Hibernate, Java Persistence API (JPA), Java Data Objects (JDO) and
    iBATIS SQL Maps for resource management, data access object (DAO)
    implementations, and transaction strategies. For example, for Hibernate
    there is first-class support with several convenient IoC features that
    address many typical Hibernate integration issues. You can configure
    all of the supported features for O/R (object relational) mapping tools through
    Dependency Injection. They can participate in Spring's resource
    and transaction management, and they comply with Spring's generic
    transaction and DAO exception hierarchies. The recommended integration
    style is to code DAOs against plain Hibernate, JPA, and JDO APIs. The
    older style of using Spring's DAO templates is no longer recommended;
    however, coverage of this style can be found in the <xref
    linkend="classic-spring-orm" /> in the appendices.</para>

    <para>Spring adds significant enhancements to the ORM layer of your choice
    when you create data access applications. You can leverage as much of the
    integration support as you wish, and you should compare this integration
    effort with the cost and risk of building a similar infrastructure
    in-house. You can use much of the ORM support as you would a library,
    regardless of technology, because everything is designed as a set of
    reusable JavaBeans. ORM in a Spring IoC container facilitates
    configuration and deployment. Thus most examples in this section show
    configuration inside a Spring container.</para>

    <para>Benefits of using the Spring Framework to create your ORM DAOs
    include:</para>

    <itemizedlist>
      <listitem>
        <para><emphasis>Easier testing.</emphasis> Spring's IoC approach makes
        it easy to swap the implementations and configuration locations of
        Hibernate <interfacename>SessionFactory</interfacename> instances,
        JDBC <interfacename>DataSource</interfacename> instances, transaction
        managers, and mapped object implementations (if needed). <!--I changed *mappes* to *mapped*; is that what you mean? Also, clarify whether *if needed* refers only to that or to the rest as well
TR: OK. Refers only to mapped object implementations-->This in turn makes it
        much easier to test each piece of persistence-related code in
        isolation.<!--deleted redundancy; sentence already refers to isolating each piece of code. TR: OK. moved isolation to the end--></para>
      </listitem>

      <listitem>
        <para><emphasis>Common data access exceptions.</emphasis> Spring can
        wrap exceptions from your ORM tool, converting them from proprietary
        (potentially checked) exceptions to a common runtime
        DataAccessException hierarchy. This feature allows you to handle most
        persistence exceptions, which are non-recoverable, only in the
        appropriate layers, without annoying boilerplate catches, throws, and
        exception declarations. You can still trap and handle exceptions as
        necessary. Remember that JDBC exceptions (including DB-specific
        dialects) are also converted to the same hierarchy, meaning that you
        can perform some operations with JDBC within a consistent programming
        model.</para>
      </listitem>

      <listitem>
        <para><emphasis>General resource management.</emphasis> Spring
        application contexts can handle the location and configuration of
        Hibernate <interfacename>SessionFactory</interfacename> instances, JPA
        <interfacename>EntityManagerFactory</interfacename> instances, JDBC
        <interfacename>DataSource</interfacename> instances, iBATIS SQL Maps
        configuration objects, and other related resources. This makes these
        values easy to manage and change. Spring offers efficient, easy, and
        safe handling of persistence resources. For example, related code that
        uses Hibernate generally needs to use the same Hibernate
        <interfacename>Session</interfacename> to ensure efficiency and proper
        transaction handling. Spring makes it easy to create and bind a
        <interfacename>Session</interfacename> to the current thread
        transparently, <!--This bullet and next refer to template wrapper class. Is this referring to using Spring DAO templates, whichis no longer recommend--><!--ed? If so, it's confusing to discuss it as an option. Sends a mixed message. If not, explain what you mean by *template* wrapper class.
TR: REVISED, PLS REVIEW. Good point, removed coverage of template wrapper.-->by
        exposing a current <interfacename>Session</interfacename> through the
        Hibernate <interfacename>SessionFactory</interfacename>. Thus Spring
        solves many chronic problems of typical Hibernate usage, for any local
        or JTA transaction environment.</para>
      </listitem>

      <listitem>
        <para><emphasis>Integrated transaction management.</emphasis> You can
        wrap your ORM code with a declarative, aspect-oriented programming
        (AOP) style method interceptor either through the
        <interfacename>@Transactional</interfacename> annotation or by
        explicitly configuring the transaction AOP advice in an XML
        configuration file. In both cases, transaction semantics and exception
        handling (rollback, and so on) are handled for you. As discussed
        below, in <!--Instead of *below*, provide link to section. TR: OK--><link
        linkend="orm-resource-mngmnt">Resource and transaction
        management</link>, you can also swap various transaction managers,
        without affecting your ORM-related code. For example, you can swap
        between local transactions and JTA, with the same full services (such
        as declarative transactions) available in both scenarios.
        Additionally, JDBC-related code can fully integrate transactionally
        with the code you use to do ORM. This is useful for data access that
        is not suitable for ORM, such as batch processing and BLOB streaming,
        which still need <!--if both batch processing and BLOB streaming need to share common transactions w/ ORM, then change *needs* to *to need*. If --><!--it refers only to BLOB streaming, say *the latter of which still needs to share...* TR: OK. Chnaged to *to need*-->to
        share common transactions with ORM operations.</para>
      </listitem>
    </itemizedlist>

    <para><!--The PetClinic sample in the Spring distribution offers alternative DAO implementations and application context configurations for JDBC,
Hibernate, and JPA. PetClinic is a working sample application that illustrates the use of Hibernate and JPA in a Spring web application.
It also leverages declarative transaction demarcation with different transaction strategies.

Beyond the samples shipped with Spring, vendors provide a variety of Spring-based ORM samples.  --><!--Name vendors, link to them? TR: WILL ADDRESS LATER. We need to point to the current samples which aren't completed yet. --><emphasis>TODO:
    provide links to current samples</emphasis></para>
  </section>

  <section xml:id="orm-general">
    <title>General ORM integration considerations</title>

    <para>This section highlights considerations that apply to all ORM
    technologies. The <xref linkend="orm-hibernate" /> section provides more
    details and also show these features and configurations in a concrete
    context.</para>

    <para>The major goal of Spring's ORM integration is clear application
    layering, with any data access and transaction technology, and for loose
    coupling of application objects. No more business service dependencies on
    the data access or transaction strategy, no more hard-coded resource
    lookups, no more hard-to-replace singletons, no more custom service
    registries. One simple and consistent approach to wiring up application
    objects, keeping them as reusable and free from container dependencies as
    possible. All the individual data access features are usable on their own
    but integrate nicely with Spring's application context concept, providing
    XML-based configuration and cross-referencing of plain JavaBean instances
    that need not be Spring-aware. In a typical Spring application, many
    important objects are JavaBeans: data access templates, data access
    objects, transaction managers, business services that use the data access
    objects and transaction managers, web view resolvers, web controllers that
    use the business services,and so on.</para>

    <section xml:id="orm-resource-mngmnt">
      <title>Resource and transaction management</title>

      <para>Typical business applications are cluttered with repetitive
      resource management code. Many projects try to invent their own
      solutions, sometimes sacrificing proper handling of failures for
      programming convenience. Spring advocates simple solutions for proper
      resource handling, namely IoC through templating<!--same question as before re templates. Does preceding refer to Spring templates that in beginning you say you no longer recommend?
TR: OK AS IS. The template for JDBC is still recommended--> in the case of
      JDBC and applying AOP interceptors for the ORM technologies.</para>

      <para>The infrastructure provides proper resource handling and
      appropriate conversion of specific API exceptions to an unchecked
      infrastructure exception hierarchy. <!--What do you mean by *cares for*? I substituted *provides*. Should it be *implements*? TR: OK-->Spring
      introduces a DAO exception hierarchy, applicable to any data access
      strategy. For direct JDBC, the <classname>JdbcTemplate</classname> class
      mentioned in a previous section provides connection handling and proper
      conversion of <classname>SQLException</classname> to the
      <classname>DataAccessException</classname> hierarchy, including
      translation of database-specific SQL error codes to meaningful exception
      classes. For ORM technologies, see the next section for how to get the
      same exception translation benefits.</para>

      <para>When it comes to transaction management, the
      <classname>JdbcTemplate</classname> class hooks in to the Spring
      transaction support and supports both JTA and JDBC transactions, through
      respective Spring transaction managers. For the supported ORM
      technologies Spring offers Hibernate, JPA and JDO support through the
      Hibernate, JPA, and JDO transaction managers as well as JTA support. For
      details on transaction support, see the <xref linkend="transaction" />
      chapter.</para>
    </section>

    <section xml:id="orm-exception-translation">
      <title>Exception translation</title>

      <para>When you use Hibernate, JPA, or JDO in a DAO, you must decide how
      to handle the persistence technology's native exception classes. The DAO
      throws a subclass of a <classname>HibernateException</classname>,
      <classname>PersistenceException</classname> or
      <interfacename>JDOException</interfacename> depending on the technology.
      These exceptions are all run-time exceptions and do not have to be
      declared or caught. You may also have to deal with
      <classname>IllegalArgumentException</classname> and
      <classname>IllegalStateException</classname>. This means that callers
      can only treat exceptions as generally fatal, unless they want to depend
      on the persistence technology's own exception structure. Catching
      specific causes such as an optimistic locking failure is not possible
      without tying the caller to the implementation strategy. This trade off
      might be acceptable to applications that are strongly ORM-based and/or
      do not need any special exception treatment. However, Spring enables
      exception translation to be applied transparently through the
      <interfacename>@Repository</interfacename> annotation:</para>

      <programlisting language="java">@Repository
public class ProductDaoImpl implements ProductDao {

    <lineannotation>// class body here...</lineannotation>

}</programlisting>

      <programlisting language="xml">&lt;beans&gt;

  <lineannotation>&lt;!-- Exception translation bean post processor --&gt;</lineannotation>
  &lt;bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"/&gt;

&lt;/beans&gt;</programlisting>

      <para>The postprocessor automatically looks for all exception
      translators (implementations of the
      <interfacename>PersistenceExceptionTranslator</interfacename> interface)
      and advises all beans marked with the
      <interfacename>@Repository</interfacename> annotation so that the
      discovered translators can intercept and apply the appropriate
      translation on the thrown exceptions.</para>

      <para>In summary: you can implement DAOs based on the plain persistence
      technology's API and annotations, while still benefiting from
      Spring-managed transactions, dependency injection, and transparent
      exception conversion (if desired) to Spring's custom exception
      hierarchies.</para>
    </section>
  </section>

  <section xml:id="orm-hibernate">
    <title>Hibernate</title>

    <para>We will start with a coverage of <link
    xl:href="http://www.hibernate.org/">Hibernate 3</link> in a Spring
    environment, using it to demonstrate the approach that Spring takes
    towards integrating O/R mappers. This section will cover many issues in
    detail and show different variations of DAO implementations and
    transaction demarcation. Most of these patterns can be directly translated
    to all other supported ORM tools. The following sections in this chapter
    will then cover the other ORM technologies, showing briefer examples
    there.</para>

    <para><note><para>As of Spring 3.0, Spring requires Hibernate 3.2 or later.</para></note></para>

    <section xml:id="orm-session-factory-setup">
      <title><interfacename>SessionFactory</interfacename> setup in a Spring
      container</title>

      <para>To avoid tying application objects to hard-coded resource lookups,
      you can define resources such as a JDBC
      <interfacename>DataSource</interfacename> or a Hibernate
      <interfacename>SessionFactory</interfacename> as beans in the Spring
      container. Application objects that need to access resources receive
      references to such predefined instances through bean references, as
      illustrated in the DAO definition in the next section.</para>

      <para>The following excerpt from an XML application context definition
      shows how to set up a JDBC <classname>DataSource</classname> and a
      Hibernate <interfacename>SessionFactory</interfacename> on top of
      it:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"&gt;
    &lt;property name="driverClassName" value="org.hsqldb.jdbcDriver"/&gt;
    &lt;property name="url" value="jdbc:hsqldb:hsql://localhost:9001"/&gt;
    &lt;property name="username" value="sa"/&gt;
    &lt;property name="password" value=""/&gt;
  &lt;/bean&gt;

  &lt;bean id="mySessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"&gt;
    &lt;property name="dataSource" ref="myDataSource"/&gt;
    &lt;property name="mappingResources"&gt;
      &lt;list&gt;
        &lt;value&gt;product.hbm.xml&lt;/value&gt;
      &lt;/list&gt;
    &lt;/property&gt;
    &lt;property name="hibernateProperties"&gt;
      &lt;value&gt;
        hibernate.dialect=org.hibernate.dialect.HSQLDialect
      &lt;/value&gt;
    &lt;/property&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>Switching from a local Jakarta Commons DBCP
      <classname>BasicDataSource</classname> to a JNDI-located
      <interfacename>DataSource</interfacename> (usually managed by an
      application server) is just a matter of configuration:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;jee:jndi-lookup id="myDataSource" jndi-name="java:comp/env/jdbc/myds"/&gt;

&lt;/beans&gt;</programlisting>

      <para>You can also access a JNDI-located
      <interfacename>SessionFactory</interfacename>, using Spring's
      <classname>JndiObjectFactoryBean</classname> /
      <literal>&lt;jee:jndi-lookup&gt;</literal> to retrieve and expose it.
      However, that is typically not common outside of an EJB context.</para>
    </section>

    <section xml:id="orm-hibernate-straight">
      <title>Implementing DAOs based on plain Hibernate 3 API</title>

      <para>Hibernate 3 has a feature called contextual sessions, wherein
      Hibernate itself manages one current
      <interfacename>Session</interfacename> per transaction. This is roughly
      equivalent to Spring's synchronization of one Hibernate
      <interfacename>Session</interfacename> per transaction. A corresponding
      DAO implementation resembles the following example, based on the plain
      Hibernate API:</para>

      <programlisting language="java">public class ProductDaoImpl implements ProductDao {

    private SessionFactory sessionFactory;

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    public Collection loadProductsByCategory(String category) {
        return this.sessionFactory.getCurrentSession()
                .createQuery("from test.Product product where product.category=?")
                .setParameter(0, category)
                .list();
    }
}</programlisting>

      <para>This style is similar to that of the Hibernate reference
      documentation and examples, except for holding the
      <interfacename>SessionFactory</interfacename> in an instance variable.
      We strongly recommend such an instance-based setup over the old-school
      <literal>static</literal> <classname>HibernateUtil</classname> class
      from Hibernate's CaveatEmptor sample application. (In general, do not
      keep any resources in <literal>static</literal> variables unless
      <emphasis>absolutely</emphasis> necessary.)</para>

      <para>The above DAO follows the dependency injection pattern: it fits
      nicely into a Spring IoC container, just as it would if coded against
      Spring's <classname>HibernateTemplate</classname>. Of course, such a DAO
      can also be set up in plain Java (for example, in unit tests). Simply
      instantiate it and call <methodname>setSessionFactory(..)</methodname>
      with the desired factory reference. As a Spring bean definition, the DAO
      would resemble the following:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"&gt;
    &lt;property name="sessionFactory" ref="mySessionFactory"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>The main advantage of this DAO style is that it depends on
      Hibernate API only; no import of any Spring class is required. This is
      of course appealing from a non-invasiveness perspective, and will no
      doubt feel more natural to Hibernate developers.</para>

      <para>However, the DAO throws plain
      <classname>HibernateException</classname> (which is unchecked, so does
      not have to be declared or caught), which means that callers can only
      treat exceptions as generally fatal - unless they want to depend on
      Hibernate's own exception hierarchy. Catching specific causes such as an
      optimistic locking failure is not possible without tying the caller to
      the implementation strategy. This trade off might be acceptable to
      applications that are strongly Hibernate-based and/or do not need any
      special exception treatment.</para>

      <para>Fortunately, Spring's
      <classname>LocalSessionFactoryBean</classname> supports Hibernate's
      <methodname>SessionFactory.getCurrentSession()</methodname> method for
      any Spring transaction strategy, returning the current Spring-managed
      transactional <interfacename>Session</interfacename> even with
      <classname>HibernateTransactionManager</classname>. Of course, the
      standard behavior of that method remains the return of the current
      <interfacename>Session</interfacename> associated with the ongoing JTA
      transaction, if any. This behavior applies regardless of whether you are
      using Spring's <classname>JtaTransactionManager</classname>, EJB
      container managed transactions (CMTs), or JTA.</para>

      <para>In summary: you can implement DAOs based on the plain Hibernate 3
      API, while still being able to participate in Spring-managed
      transactions.</para>
    </section>

    <section xml:id="orm-hibernate-tx-declarative">
      <title>Declarative transaction demarcation</title>

      <para>We recommend that you use Spring's declarative transaction
      support, which enables you to replace explicit transaction demarcation
      API calls in your Java code with an AOP transaction interceptor. This
      transaction interceptor can be configured in a Spring container using
      either Java annotations or XML.<!--Reword last part of preceding sentence to clarify *what* is *using Java annotations or XML*. Are you using Java annotations or XML to replace--><!--explicit transaction demarcation API calls, etc. OR are you saying the Spring container is using these?
TR: REVISED, PLS REVIEW.-->This declarative transaction capability allows you
      to keep business services free of repetitive transaction demarcation
      code and to focus on adding business logic, which is the real value of
      your application.</para>

      <note>
        <para>Prior to continuing, you are <emphasis>strongly</emphasis>
        encouraged to read <xref linkend="transaction-declarative" /> if you
        have not done so.</para>
      </note>

      <para>Furthermore, transaction semantics like propagation behavior and
      isolation level can be changed in a configuration file and do not affect
      the business service implementations.<!--give context to example; what is it showing, what is its purpose? TR: REVISED, PLS REVIEW. Added some context.--></para>

      <para>The following example shows how you can configure an AOP
      transaction interceptor, using XML, for a simple service class:</para>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd"&gt;

  <lineannotation>&lt;!-- SessionFactory, DataSource, etc. omitted --&gt;</lineannotation>

  &lt;bean id="transactionManager"
            class="org.springframework.orm.hibernate3.HibernateTransactionManager"&gt;
    &lt;property name="sessionFactory" ref="sessionFactory"/&gt;
  &lt;/bean&gt;

  &lt;aop:config&gt;
    &lt;aop:pointcut id="productServiceMethods"
            expression="execution(* product.ProductService.*(..))"/&gt;
    &lt;aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/&gt;
  &lt;/aop:config&gt;

  &lt;tx:advice id="txAdvice" transaction-manager="myTxManager"&gt;
    &lt;tx:attributes&gt;
      &lt;tx:method name="increasePrice*" propagation="REQUIRED"/&gt;
      &lt;tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/&gt;
      &lt;tx:method name="*" propagation="SUPPORTS" read-only="true"/&gt;
    &lt;/tx:attributes&gt;
  &lt;/tx:advice&gt;

  &lt;bean id="myProductService" class="product.SimpleProductService"&gt;
    &lt;property name="productDao" ref="myProductDao"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>This is the service class that is advised:</para>

      <programlisting language="java">public class ProductServiceImpl implements ProductService {

    private ProductDao productDao;

    public void setProductDao(ProductDao productDao) {
        this.productDao = productDao;
    }

    <lineannotation>// notice the absence of transaction demarcation code in this method</lineannotation>
    <lineannotation>// Spring's declarative transaction infrastructure will be demarcating</lineannotation>
    <lineannotation>// transactions on your behalf </lineannotation>
    public void increasePriceOfAllProductsInCategory(final String category) {
        List productsToChange = this.productDao.loadProductsByCategory(category);
        <lineannotation>// ...</lineannotation>
    }
}</programlisting>

      <para>We also show an attribute-support based configuration, in the
      following example. <!--I added *in the following example*; is this correct? Relate example below to the one that follows it. TR: OK-->You
      annotate the service layer with @Transactional annotations and instruct
      the Spring container to find these annotations and provide transactional
      semantics for these annotated methods.</para>

      <programlisting language="java">public class ProductServiceImpl implements ProductService {

    private ProductDao productDao;

    public void setProductDao(ProductDao productDao) {
        this.productDao = productDao;
    }

    @Transactional
    public void increasePriceOfAllProductsInCategory(final String category) {
        List productsToChange = this.productDao.loadProductsByCategory(category);
        <lineannotation>// ...</lineannotation>
    }

    @Transactional(readOnly = true)
    public List&lt;Product&gt; findAllProducts() {
        return this.productDao.findAllProducts();
    }

}</programlisting>

      <para>As you can see from the following configuration example, the
      configuration is much simplified, compared to the XML example above,
      while still providing the same functionality driven by the annotations
      in the service layer code. All you need to provide is the
      TransactionManager implementation and a "&lt;tx:annotation-driven/&gt;"
      entry.<!--What does preceding example show, what's its relation to this example? TR: REVISED, PLS REVIEW.--></para>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd"&gt;

  <lineannotation>&lt;!-- SessionFactory, DataSource, etc. omitted --&gt;</lineannotation>

  &lt;bean id="transactionManager"
            class="org.springframework.orm.hibernate3.HibernateTransactionManager"&gt;
    &lt;property name="sessionFactory" ref="sessionFactory"/&gt;
  &lt;/bean&gt;

  &lt;tx:annotation-driven/&gt;

  &lt;bean id="myProductService" class="product.SimpleProductService"&gt;
    &lt;property name="productDao" ref="myProductDao"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>
    </section>

    <section xml:id="orm-hibernate-tx-programmatic">
      <title>Programmatic transaction demarcation</title>

      <para>You can demarcate transactions in a higher level of the
      application, on top of such lower-level data access services spanning
      any number of operations. Nor do restrictions exist on the
      implementation of the surrounding business service; it just needs a
      Spring <classname>PlatformTransactionManager</classname>. Again, the
      latter can come from anywhere, but preferably as a bean reference
      through a <methodname>setTransactionManager(..)</methodname> method,
      just as the <classname>productDAO</classname> should be set by a
      <methodname>setProductDao(..)</methodname> method. The following
      snippets show a transaction manager and a business service definition in
      a Spring application context, and an example for a business method
      implementation:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myTxManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"&gt;
    &lt;property name="sessionFactory" ref="mySessionFactory"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myProductService" class="product.ProductServiceImpl"&gt;
    &lt;property name="transactionManager" ref="myTxManager"/&gt;
    &lt;property name="productDao" ref="myProductDao"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <programlisting language="java">public class ProductServiceImpl implements ProductService {

    private TransactionTemplate transactionTemplate;
    private ProductDao productDao;

    public void setTransactionManager(PlatformTransactionManager transactionManager) {
        this.transactionTemplate = new TransactionTemplate(transactionManager);
    }

    public void setProductDao(ProductDao productDao) {
        this.productDao = productDao;
    }

    public void increasePriceOfAllProductsInCategory(final String category) {
        this.transactionTemplate.execute(new TransactionCallbackWithoutResult() {

                public void doInTransactionWithoutResult(TransactionStatus status) {
                    List productsToChange = this.productDao.loadProductsByCategory(category);
                    <lineannotation>// do the price increase...</lineannotation>
                }
            }
        );
    }
}</programlisting>

      <para>Spring's <classname>TransactionInterceptor</classname> allows any
      checked application exception to be thrown with the callback code, while
      <classname>TransactionTemplate</classname> is restricted to unchecked
      exceptions within the callback.
      <classname>TransactionTemplate</classname> triggers a rollback in case
      of an unchecked application exception, or if the transaction is marked
      rollback-only by the application (via
      <classname>TransactionStatus</classname>).
      <classname>TransactionInterceptor</classname> behaves the same way by
      default but allows configurable rollback policies per method.</para>
    </section>

    <section xml:id="orm-hibernate-tx-strategies">
      <title>Transaction management strategies</title>

      <para>Both <classname>TransactionTemplate</classname> and
      <classname>TransactionInterceptor</classname> delegate the actual
      transaction handling to a
      <classname>PlatformTransactionManager</classname> instance, which can be
      a <classname>HibernateTransactionManager</classname> (for a single
      Hibernate <interfacename>SessionFactory</interfacename>, using a
      <classname>ThreadLocal</classname>
      <interfacename>Session</interfacename> under the hood) or a
      <classname>JtaTransactionManager</classname> (delegating to the JTA
      subsystem of the container) for Hibernate applications. You can even use
      a custom <classname>PlatformTransactionManager</classname>
      implementation. Switching from native Hibernate transaction management
      to JTA, such as when facing distributed transaction requirements for
      certain deployments of your application, is just a matter of
      configuration. Simply replace the Hibernate transaction manager with
      Spring's JTA transaction implementation. Both transaction demarcation
      and data access code will work without changes, because they just use
      the generic transaction management APIs.</para>

      <para>For distributed transactions across multiple Hibernate session
      factories, simply combine <classname>JtaTransactionManager</classname>
      as a transaction strategy with multiple
      <classname>LocalSessionFactoryBean</classname> definitions. Each DAO
      then gets one specific <interfacename>SessionFactory</interfacename>
      reference passed into its corresponding bean property. If all underlying
      JDBC data sources are transactional container ones, a business service
      can demarcate transactions across any number of DAOs and any number of
      session factories without special regard, as long as it is using
      <classname>JtaTransactionManager</classname> as the strategy.</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;jee:jndi-lookup id="dataSource1" jndi-name="java:comp/env/jdbc/myds1"/&gt;

  &lt;jee:jndi-lookup id="dataSource2" jndi-name="java:comp/env/jdbc/myds2"/&gt;

  &lt;bean id="mySessionFactory1"
            class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"&gt;
    &lt;property name="dataSource" ref="myDataSource1"/&gt;
    &lt;property name="mappingResources"&gt;
      &lt;list&gt;
        &lt;value&gt;product.hbm.xml&lt;/value&gt;
      &lt;/list&gt;
    &lt;/property&gt;
    &lt;property name="hibernateProperties"&gt;
      &lt;value&gt;
        hibernate.dialect=org.hibernate.dialect.MySQLDialect
        hibernate.show_sql=true
      &lt;/value&gt;
    &lt;/property&gt;
  &lt;/bean&gt;

  &lt;bean id="mySessionFactory2"
            class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"&gt;
    &lt;property name="dataSource" ref="myDataSource2"/&gt;
    &lt;property name="mappingResources"&gt;
      &lt;list&gt;
        &lt;value&gt;inventory.hbm.xml&lt;/value&gt;
      &lt;/list&gt;
    &lt;/property&gt;
    &lt;property name="hibernateProperties"&gt;
      &lt;value&gt;
        hibernate.dialect=org.hibernate.dialect.OracleDialect
      &lt;/value&gt;
    &lt;/property&gt;
  &lt;/bean&gt;

  &lt;bean id="myTxManager" class="org.springframework.transaction.jta.JtaTransactionManager"/&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"&gt;
    &lt;property name="sessionFactory" ref="mySessionFactory1"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myInventoryDao" class="product.InventoryDaoImpl"&gt;
    &lt;property name="sessionFactory" ref="mySessionFactory2"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myProductService" class="product.ProductServiceImpl"&gt;
    &lt;property name="productDao" ref="myProductDao"/&gt;
    &lt;property name="inventoryDao" ref="myInventoryDao"/&gt;
  &lt;/bean&gt;

  &lt;aop:config&gt;
    &lt;aop:pointcut id="productServiceMethods"
                expression="execution(* product.ProductService.*(..))"/&gt;
    &lt;aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/&gt;
  &lt;/aop:config&gt;

  &lt;tx:advice id="txAdvice" transaction-manager="myTxManager"&gt;
    &lt;tx:attributes&gt;
      &lt;tx:method name="increasePrice*" propagation="REQUIRED"/&gt;
      &lt;tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/&gt;
      &lt;tx:method name="*" propagation="SUPPORTS" read-only="true"/&gt;
    &lt;/tx:attributes&gt;
  &lt;/tx:advice&gt;

&lt;/beans&gt;</programlisting>

      <para>Both <classname>HibernateTransactionManager</classname> and
      <classname>JtaTransactionManager</classname> allow for proper JVM-level
      cache handling with Hibernate, without container-specific transaction
      manager lookup or a JCA connector (if you are not using EJB to initiate
      transactions).<!--Is it clear that the parenthetical phrase applies to only *JCA connector* or does it apply to *without transaction manager lookup* also?
TR: OK. Reads OK to me, it applies to both. --></para>

      <para><classname>HibernateTransactionManager</classname> can export the
      Hibernate JDBC <interfacename>Connection</interfacename> to plain JDBC
      access code, for a specific <interfacename>DataSource</interfacename>.
      This capability allows for high-level transaction demarcation with mixed
      Hibernate and JDBC data access completely without JTA, if you are
      accessing only one database.
      <classname>HibernateTransactionManager</classname> automatically exposes
      the Hibernate transaction as a JDBC transaction if you have set up the
      passed-in <interfacename>SessionFactory</interfacename> with a
      <interfacename>DataSource</interfacename> through the
      <classname>dataSource</classname> property of the
      <classname>LocalSessionFactoryBean</classname> class. Alternatively, you
      can specify explicitly the <interfacename>DataSource</interfacename> for
      which the transactions are supposed to be exposed through the
      <classname>dataSource</classname> property of the
      <classname>HibernateTransactionManager</classname> class.</para>
    </section>

    <section xml:id="orm-hibernate-resources">
      <title>Comparing container-managed and locally defined resources<!--I've revised to better communicate the point of the section, which I think has to do with --><!--comparing spring's local support for transactions as opposed to container support. Revise as necessary.
TR: REVISED, PLS REVIEW. Changed to heading *resources* since it technically could be more than transactions i.e. caching--></title>

      <para>You can switch between a container-managed JNDI
      <interfacename>SessionFactory</interfacename><!--Clarify whether JNDI SessionFactory refers to container resources; I'm not sure what's being compared.
TR: REVISED, PLS REVIEW. Clarified by addin container-managed.--> and a
      locally defined one, without having to change a single line of
      application code. Whether to keep resource definitions in the container
      or locally within the application is mainly a matter of the transaction
      strategy that you use. Compared to a Spring-defined local
      <interfacename>SessionFactory</interfacename>, a manually registered
      JNDI <interfacename>SessionFactory</interfacename> does not provide any
      benefits. Deploying a <interfacename>SessionFactory</interfacename>
      through Hibernate's JCA connector provides the added value of
      participating in the Java EE server's management infrastructure, but
      does not add actual value beyond that.</para>

      <para>Spring's transaction support is not bound to a container.
      Configured with any strategy other than JTA, transaction support also
      works in a stand-alone or test environment. Especially in the typical
      case of single-database transactions, Spring's single-resource local
      transaction support <!--I wrote *stand-alone transaction support*; if not correct, specify what you mean by *this*.
TR: REVISED, PLS REVIEW. Changed to single-resource local transaction support.-->is
      a lightweight and powerful alternative to JTA. When you use local EJB
      stateless session beans to drive transactions, you depend both on an EJB
      container and JTA, even if you access only a single database, and only
      use stateless session beans to provide declarative transactions through
      container-managed transactions. <!--Does the next sentence refer to Spring or non-Spring? Clarify. I'm not sure whether the point of this paragraph and preceding is clear.
TR: REVISED, PLS REVIEW. It's not very clear. I've revised it. It refers to non-Spring programmatic use of JTA.-->Also,
      direct use of JTA programmatically requires a Java EE environment as
      well. JTA does not involve only container dependencies in terms of JTA
      itself and of JNDI <interfacename>DataSource</interfacename> instances.
      For non-Spring, JTA-driven Hibernate transactions, you have to use the
      Hibernate JCA connector, or extra Hibernate transaction code with the
      <interfacename>TransactionManagerLookup</interfacename> configured for
      proper JVM-level caching.</para>

      <para>Spring-driven transactions can work as well with a locally defined
      Hibernate <interfacename>SessionFactory</interfacename> as they do with
      a local JDBC <interfacename>DataSource </interfacename>if they are
      accessing a single database. Thus you only have to use Spring's JTA
      transaction strategy when you have distributed transaction requirements.
      A JCA connector requires container-specific deployment steps, and
      obviously JCA support in the first place. This configuration requires
      more work than deploying a simple web application with local resource
      definitions and Spring-driven transactions. Also, you often need the
      Enterprise Edition of your container if you are using, for example,
      WebLogic Express, which does not provide JCA. A Spring application with
      local resources and transactions spanning one single database works in
      any Java EE web container (without JTA, JCA, or EJB) such as Tomcat,
      Resin, or even plain Jetty. Additionally, you can easily reuse such a
      middle tier in desktop applications or test suites.</para>

      <para>All things considered, if you do not use EJBs, stick with local
      <interfacename>SessionFactory</interfacename> setup and Spring's
      <classname>HibernateTransactionManager</classname> or
      <classname>JtaTransactionManager</classname>. You get all of the
      benefits, including proper transactional JVM-level caching and
      distributed transactions, without the inconvenience of container
      deployment. JNDI registration of a Hibernate
      <interfacename>SessionFactory</interfacename> through the JCA connector
      only adds value when used in conjunction with EJBs.</para>
    </section>

    <section xml:id="orm-hibernate-invalid-jdbc-access-error">
      <title>Spurious application server warnings with Hibernate</title>

      <para>In some JTA environments with very strict
      <interfacename>XADataSource</interfacename> implementations -- currently
      only some WebLogic Server and WebSphere versions -- when Hibernate is
      configured without regard to the JTA
      <interfacename>PlatformTransactionManager</interfacename> object for
      that environment, it is possible for spurious warning or exceptions to
      show up in the application server log. These warnings or exceptions
      indicate that the connection being accessed is no longer valid, or JDBC
      access is no longer valid, possibly because the transaction is no longer
      active. As an example, here is an actual exception from WebLogic:</para>

      <programlisting>java.sql.SQLException: The transaction is no longer active - status: 'Committed'.
   No further JDBC access is allowed within this transaction.</programlisting>

      <para>You resolve this warning by simply making Hibernate aware of the
      JTA <interfacename>PlatformTransactionManager</interfacename> instance,
      to which it will synchronize (along with Spring). You have two options
      for doing this:</para>

      <itemizedlist>
        <listitem>
          <para>If in your application context you are already directly
          obtaining the JTA
          <interfacename>PlatformTransactionManager</interfacename> object
          (presumably from JNDI through
          <literal>JndiObjectFactoryBean</literal> or <literal>&lt;jee:jndi-lookup&gt;</literal>)
          and feeding it, for example, to Spring's
          <classname>JtaTransactionManager</classname>, then the easiest way
          is to specify a reference to the bean defining this JTA
          <interfacename>PlatformTransactionManager</interfacename>
          instance<!--Replace *this* with exactly what *this* refes to--> as
          the value of the <property>jtaTransactionManager</property> property
          for <classname>LocalSessionFactoryBean.</classname> Spring then makes
          the object available to Hibernate.</para>
        </listitem>

        <listitem>
          <para>More likely you do not already have the JTA
          <interfacename>PlatformTransactionManager</interfacename> instance,
          because Spring's <classname>JtaTransactionManager</classname> can
          find it itself. <!--Re preceding sentence, if this is the case, then why would you need to do what first bullet describes?
TR: OK AS IS. This is very container dependent, and either case is possible.-->Thus
          you need to configure Hibernate to look up JTA
          <interfacename>PlatformTransactionManager</interfacename> directly.
          You do this by configuring an application server- specific
          <literal>TransactionManagerLookup</literal> class in the Hibernate
          configuration, as described in the Hibernate manual.</para>
        </listitem>
      </itemizedlist>

      <para>The remainder of this section describes the sequence of events
      that occur with and without Hibernate's awareness of the JTA
      <interfacename>PlatformTransactionManager</interfacename>.</para>

      <para>When Hibernate is not configured with any awareness of the JTA
      <interfacename>PlatformTransactionManager</interfacename>, the following
      events occur when a JTA transaction commits:</para>

      <orderedlist>
        <listitem>
          <para>The JTA transaction commits.</para>
        </listitem>

        <listitem>
          <para>Spring's <classname>JtaTransactionManager</classname> is
          synchronized to the JTA transaction, so it is called back through an
          <emphasis>afterCompletion</emphasis> callback by the JTA transaction
          manager.</para>
        </listitem>

        <listitem>
          <para>Among other activities, this synchronization<!--Identify *this*. TR: REVISED, PLS REVIEW. Added "synchronization"--> can
          trigger a callback by Spring to Hibernate, through Hibernate's
          <literal>afterTransactionCompletion</literal> callback <!--Preceding line, is *afterTransactionCompletion* callback the same as *afterCompletion* callback in step 2? If so, revise so --><!--there is no redundancy, or at least refer to the two callbacks in the same way.
TR: OK AS IS. Two different callback methhods - one is Spring's (*afterCompletion*) and the other is Hibernate's (*afterTransactionCompletion*)-->(used
          to clear the Hibernate cache), followed by an explicit
          <literal>close()</literal> call on the Hibernate Session, which
          causes Hibernate to attempt to <literal>close()</literal> the JDBC
          Connection.</para>
        </listitem>

        <listitem>
          <para>In some environments, this
          <methodname>Connection.close()</methodname> call then triggers the
          warning or error, as the application server no longer considers the
          <interfacename>Connection</interfacename> usable at all, because the
          transaction has already been committed.</para>
        </listitem>
      </orderedlist>

      <para>When Hibernate is configured with awareness of the JTA
      <interfacename>PlatformTransactionManager</interfacename>, the following
      events occur when a JTA transaction commits:</para>

      <orderedlist>
        <listitem>
          <para>the JTA transaction is ready to commit.</para>
        </listitem>

        <listitem>
          <para>Spring's <classname>JtaTransactionManager</classname> is
          synchronized to the JTA transaction, so the transaction is called
          back through a <emphasis>beforeCompletion</emphasis> callback by the
          JTA transaction manager.</para>
        </listitem>

        <listitem>
          <para>Spring is aware that Hibernate itself is synchronized to the
          JTA transaction, and behaves differently than in the previous
          scenario. Assuming the Hibernate
          <interfacename>Session</interfacename> needs to be closed at all,
          Spring will close it now.</para>
        </listitem>

        <listitem>
          <para>The JTA transaction commits.</para>
        </listitem>

        <listitem>
          <para>Hibernate is synchronized to the JTA transaction, so the
          transaction is called back through an
          <emphasis>afterCompletion</emphasis> callback by the JTA transaction
          manager, and can properly clear its cache.</para>
        </listitem>
      </orderedlist>
    </section>
  </section>

  <section xml:id="orm-jdo">
    <title>JDO</title>

    <para>Spring supports the standard JDO 2.0 and 2.1 APIs as data access
    strategy, following the same style as the Hibernate support. The
    corresponding integration classes reside in the
    <literal>org.springframework.orm.jdo</literal> package.</para>

    <section xml:id="orm-jdo-setup">
      <title><interfacename>PersistenceManagerFactory</interfacename>
      setup</title>

      <para>Spring provides a
      <classname>LocalPersistenceManagerFactoryBean</classname> class that
      allows you to define a local JDO
      <interfacename>PersistenceManagerFactory</interfacename> within a Spring
      application context:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myPmf" class="org.springframework.orm.jdo.LocalPersistenceManagerFactoryBean"&gt;
    &lt;property name="configLocation" value="classpath:kodo.properties"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>Alternatively, you can set up a
      <interfacename>PersistenceManagerFactory</interfacename> through direct
      instantiation of a
      <interfacename>PersistenceManagerFactory</interfacename> implementation
      class. A JDO <interfacename>PersistenceManagerFactory</interfacename>
      implementation class follows the JavaBeans pattern, just like a JDBC
      <interfacename>DataSource</interfacename> implementation class, which is
      a natural fit for a configuration that uses Spring. This setup style
      usually supports a Spring-defined JDBC
      <interfacename>DataSource</interfacename>, passed into the
      <classname>connectionFactory</classname> property. For example, for the
      open source JDO implementation DataNucleus (formerly JPOX) (<link
      xl:href="http://www.datanucleus.org/">http://www.datanucleus.org/</link>),
      this is the XML configuration of the
      <interfacename>PersistenceManagerFactory</interfacename>
      implementation:<!--complete the intro sentence; what does this example show? What is its purpose? TR: REVISED, PLS REVIEW.--></para>

      <programlisting language="xml">&lt;beans&gt;

 &lt;bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"&gt;
   &lt;property name="driverClassName" value="${jdbc.driverClassName}"/&gt;
   &lt;property name="url" value="${jdbc.url}"/&gt;
   &lt;property name="username" value="${jdbc.username}"/&gt;
   &lt;property name="password" value="${jdbc.password}"/&gt;
 &lt;/bean&gt;

 &lt;bean id="myPmf" class="org.datanucleus.jdo.JDOPersistenceManagerFactory" destroy-method="close"&gt;
   &lt;property name="connectionFactory" ref="dataSource"/&gt;
   &lt;property name="nontransactionalRead" value="true"/&gt;
 &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>You can also set up JDO
      <interfacename>PersistenceManagerFactory</interfacename> in the JNDI
      environment of a Java EE application server, usually through the JCA
      connector provided by the particular JDO implementation. Spring's
      standard <literal>JndiObjectFactoryBean</literal> or
      <literal>&lt;jee:jndi-lookup&gt;</literal> can be used to
      retrieve and expose such a
      <interfacename>PersistenceManagerFactory</interfacename>. However,
      outside an EJB context, no real benefit exists in holding the
      <interfacename>PersistenceManagerFactory</interfacename> in JNDI: only
      choose such a setup for a good reason. See <xref
      linkend="orm-hibernate-resources" /> for a discussion; the arguments
      there apply to JDO as well.</para>
    </section>

    <section xml:id="orm-jdo-daos-straight">
      <title>Implementing DAOs based on the plain JDO API</title>

      <para>DAOs can also be written directly against plain JDO API, without
      any Spring dependencies, by using an injected
      <interfacename>PersistenceManagerFactory</interfacename>. The following
      is an example of a corresponding DAO implementation:</para>

      <programlisting language="java">public class ProductDaoImpl implements ProductDao {

    private PersistenceManagerFactory persistenceManagerFactory;

    public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) {
        this.persistenceManagerFactory = pmf;
    }

    public Collection loadProductsByCategory(String category) {
        PersistenceManager pm = this.persistenceManagerFactory.getPersistenceManager();
        try {
            Query query = pm.newQuery(Product.class, "category = pCategory");
            query.declareParameters("String pCategory");
            return query.execute(category);
        }
        finally {
          pm.close();
        }
    }
}</programlisting>

      <para>Because the above DAO follows the dependency injection pattern, it
      fits nicely into a Spring container, just as it would if coded against
      Spring's <classname>JdoTemplate</classname>:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"&gt;
    &lt;property name="persistenceManagerFactory" ref="myPmf"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>The main problem with such DAOs is that they always get a new
      <interfacename>PersistenceManager</interfacename> from the factory. To
      access a Spring-managed transactional
      <interfacename>PersistenceManager</interfacename>, define a
      <classname>TransactionAwarePersistenceManagerFactoryProxy</classname>
      (as included in Spring) in front of your target
      <interfacename>PersistenceManagerFactory</interfacename>, then passing a
      reference to that proxy into your DAOs as in the following example:<!--Revise to clarify *what* is passing the proxy into DAOs? How does that relate to rest of the sentence? TR: REVISED, PLS REVIEW.--></para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myPmfProxy"
      class="org.springframework.orm.jdo.TransactionAwarePersistenceManagerFactoryProxy"&gt;
    &lt;property name="targetPersistenceManagerFactory" ref="myPmf"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"&gt;
    &lt;property name="persistenceManagerFactory" ref="myPmfProxy"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>Your data access code will receive a transactional
      <interfacename>PersistenceManager</interfacename> (if any) from the
      <methodname>PersistenceManagerFactory.getPersistenceManager()</methodname>
      method that it calls. The latter method call goes through the proxy,
      which first checks for a current transactional
      <interfacename>PersistenceManager</interfacename> before getting a new
      one from the factory. Any <methodname>close()</methodname> calls on the
      <interfacename>PersistenceManager</interfacename> are ignored in case of
      a transactional
      <interfacename>PersistenceManager</interfacename>.</para>

      <para>If your data access code always runs within an active transaction
      (or at least within active transaction synchronization), it is safe to
      omit the <methodname>PersistenceManager.close()</methodname> call and
      thus the entire <literal>finally</literal> block, which you might do to
      keep your DAO implementations concise:</para>

      <programlisting language="java">public class ProductDaoImpl implements ProductDao {

    private PersistenceManagerFactory persistenceManagerFactory;

    public void setPersistenceManagerFactory(PersistenceManagerFactory pmf) {
        this.persistenceManagerFactory = pmf;
    }

    public Collection loadProductsByCategory(String category) {
        PersistenceManager pm = this.persistenceManagerFactory.getPersistenceManager();
        Query query = pm.newQuery(Product.class, "category = pCategory");
        query.declareParameters("String pCategory");
        return query.execute(category);
    }
}</programlisting>

      <para>With such DAOs that rely on active transactions, it is recommended
      that you enforce active transactions through turning off
      <classname>TransactionAwarePersistenceManagerFactoryProxy</classname>'s
      <classname>allowCreate</classname> flag:</para>

      <programlisting language="xml">&lt;beans&gt;

  &lt;bean id="myPmfProxy"
      class="org.springframework.orm.jdo.TransactionAwarePersistenceManagerFactoryProxy"&gt;
    &lt;property name="targetPersistenceManagerFactory" ref="myPmf"/&gt;
    &lt;property name="allowCreate" value="false"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"&gt;
    &lt;property name="persistenceManagerFactory" ref="myPmfProxy"/&gt;
  &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

      <para>The main advantage of this DAO style is that it depends on JDO API
      only; no import of any Spring class is required. This is of course
      appealing from a non-invasiveness perspective, and might feel more
      natural to JDO developers.</para>

      <para>However, the DAO throws plain
      <exceptionname>JDOException</exceptionname> (which is unchecked, so does
      not have to be declared or caught), which means that callers can only
      treat exceptions as fatal, unless you want to depend on JDO's own
      exception structure. Catching specific causes such as an optimistic
      locking failure is not possible without tying the caller to the
      implementation strategy. This trade off might be acceptable to
      applications that are strongly JDO-based and/or do not need any special
      exception treatment.</para>

      <para>In summary, you can DAOs based on the plain JDO API, and they can
      still participate in Spring-managed transactions. This strategy might
      appeal to you if you are already familiar with JDO. However, such DAOs
      throw plain <exceptionname>JDOException</exceptionname>, and you would
      have to convert explicitly to Spring's
      <exceptionname>DataAccessException</exceptionname> (if desired).</para>
    </section>

    <section xml:id="orm-jdo-tx">
      <title>Transaction management</title>

      <note>
        <para>You are <emphasis>strongly</emphasis> encouraged to read <xref
        linkend="transaction-declarative" /> if you have not done so, to get a
        more detailed coverage of Spring's declarative transaction
        support.</para>
      </note>

      <para>To execute service operations within transactions, you can use
      Spring's common declarative transaction facilities. For example:</para>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans
        xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:aop="http://www.springframework.org/schema/aop"
        xmlns:tx="http://www.springframework.org/schema/tx"
        xsi:schemaLocation="
   http://www.springframework.org/schema/beans
   http://www.springframework.org/schema/beans/spring-beans.xsd
   http://www.springframework.org/schema/tx
   http://www.springframework.org/schema/tx/spring-tx.xsd
   http://www.springframework.org/schema/aop
   http://www.springframework.org/schema/aop/spring-aop.xsd"&gt;

  &lt;bean id="myTxManager" class="org.springframework.orm.jdo.JdoTransactionManager"&gt;
    &lt;property name="persistenceManagerFactory" ref="myPmf"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myProductService" class="product.ProductServiceImpl"&gt;
    &lt;property name="productDao" ref="myProductDao"/&gt;
  &lt;/bean&gt;

  &lt;tx:advice id="txAdvice" transaction-manager="txManager"&gt;
    &lt;tx:attributes&gt;
      &lt;tx:method name="increasePrice*" propagation="REQUIRED"/&gt;
      &lt;tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/&gt;
      &lt;tx:method name="*" propagation="SUPPORTS" read-only="true"/&gt;
    &lt;/tx:attributes&gt;
  &lt;/tx:advice&gt;

  &lt;aop:config&gt;
    &lt;aop:pointcut id="productServiceMethods"
            expression="execution(* product.ProductService.*(..))"/&gt;
    &lt;aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/&gt;
  &lt;/aop:config&gt;

&lt;/beans&gt;</programlisting>

      <para>JDO requires an active transaction to modify a persistent object.
      The non-transactional flush concept does not exist in JDO, in contrast
      to Hibernate. For this reason, you need to set up the chosen JDO
      implementation for a specific environment. Specifically, you need to set
      it up explicitly for JTA synchronization, to detect an active JTA
      transaction itself. This is not necessary for local transactions as
      performed by Spring's <classname>JdoTransactionManager</classname>, but
      it is necessary to participate in JTA transactions, whether driven by
      Spring's <classname>JtaTransactionManager</classname> or by EJB CMT and
      plain JTA.</para>

      <para><classname>JdoTransactionManager</classname> is capable of
      exposing a JDO transaction to JDBC access code that accesses the same
      JDBC <interfacename>DataSource</interfacename>, provided that the
      registered <classname>JdoDialect</classname> supports retrieval of the
      underlying JDBC <interfacename>Connection</interfacename>. This is the
      case for JDBC-based JDO 2.0 implementations by default.</para>
    </section>

    <section xml:id="orm-jdo-dialect">
      <title><interfacename>JdoDialect</interfacename></title>

      <para>As an advanced feature, both <classname>JdoTemplate</classname>
      and <classname>JdoTransactionManager</classname> support a custom
      <interfacename>JdoDialect</interfacename> that can be passed into the
      <code>jdoDialect</code> bean property. In this scenario, the DAOs will
      not receive a <interfacename>PersistenceManagerFactory</interfacename>
      reference but rather a full <classname>JdoTemplate</classname> instance
      (for example, passed into the <literal>jdoTemplate</literal>
      property of <classname>JdoDaoSupport</classname>). Using a
      <interfacename>JdoDialect</interfacename> implementation, you can enable
      advanced features supported by Spring, usually in a vendor-specific
      manner:</para>

      <itemizedlist>
        <listitem>
          <para>Applying specific transaction semantics such as custom
          isolation level or transaction timeout</para>
        </listitem>

        <listitem>
          <para>Retrieving the transactional JDBC
          <interfacename>Connection</interfacename> for exposure to JDBC-based
          DAOs</para>
        </listitem>

        <listitem>
          <para>Applying query timeouts, which are automatically calculated
          from Spring-managed transaction timeouts</para>
        </listitem>

        <listitem>
          <para>Eagerly flushing a
          <interfacename>PersistenceManager,</interfacename> to make
          transactional changes visible to JDBC-based data access code</para>
        </listitem>

        <listitem>
          <para>Advanced translation of <literal>JDOExceptions</literal> to
          Spring <literal>DataAccessExceptions</literal></para>
        </listitem>
      </itemizedlist>

      <para>See the <classname>JdoDialect</classname> Javadoc for more details
      on its operations and how to use them within Spring's JDO
      support.</para>
    </section>
  </section>

  <section xml:id="orm-jpa">
    <title>JPA</title>

    <para>The Spring JPA, available under the
    <literal>org.springframework.orm.jpa</literal> package, offers
    comprehensive support for the <link
    xl:href="http://java.sun.com/developer/technicalArticles/J2EE/jpa/index.html">Java
    Persistence API</link> in a similar manner to the integration with
    Hibernate or JDO, while being aware of the underlying implementation in
    order to provide additional features.</para>

    <section xml:id="orm-jpa-setup">
      <title>Three options for JPA setup in a Spring environment</title>

      <para>The Spring JPA support offers three ways of setting up the JPA
      <interfacename>EntityManagerFactory</interfacename> that will be used by
      the application to obtain an entity manager.<!--Define and give purpose of JPA EntityManagerFactory. TR: REVISED, PLS REVIEW.--></para>

      <section xml:id="orm-jpa-setup-lemfb">
        <title><classname>LocalEntityManagerFactoryBean</classname></title>

        <note>
          <para>Only use this option in simple deployment environments such as
          stand-alone applications and integration tests.</para>
        </note>

        <para>The <classname>LocalEntityManagerFactoryBean</classname> creates
        an <interfacename>EntityManagerFactory</interfacename> suitable for
        simple deployment environments where the application uses only JPA for
        data access. <!--Note says use option only for stand-alone apps and testing; does that conflict with preceding line re data access?
TR: REVISED, PLS REVIEW.-->The factory bean uses the JPA
        <interfacename>PersistenceProvider</interfacename> autodetection
        mechanism (according to JPA's Java SE bootstrapping) and, in most
        cases, requires you to specify only the persistence unit name:</para>

        <programlisting language="xml">&lt;beans&gt;

   &lt;bean id="myEmf" class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean"&gt;
      &lt;property name="persistenceUnitName" value="myPersistenceUnit"/&gt;
   &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

        <para>This form of JPA deployment is the simplest and the most
        limited. You cannot refer <!--cannot link *what* to an existing datasource? TR: REVISED, PLS REVIEW.-->to
        an existing JDBC <interfacename>DataSource</interfacename> bean
        definition and no support for global transactions exists. Furthermore,
        weaving (byte-code transformation) of persistent classes is
        provider-specific, often requiring a specific JVM agent to specified
        on startup. This option is sufficient only for stand-alone
        applications and test environments, for which the JPA specification is
        designed.</para>
      </section>

      <section xml:id="orm-jpa-setup-jndi">
        <title>Obtaining an <classname>EntityManagerFactory</classname> from
        JNDI</title>

        <note>
          <para>Use this option when deploying to a Java EE 5 server. Check
          your server's documentation on how to deploy a custom JPA provider
          into your server, allowing for a different provider than the
          server's default.</para>
        </note>

        <para>Obtaining an <interfacename>EntityManagerFactory</interfacename>
        from JNDI (for example in a Java EE 5 environment), is simply a matter
        of changing the XML configuration:</para>

        <programlisting language="xml">&lt;beans&gt;

    &lt;jee:jndi-lookup id="myEmf" jndi-name="persistence/myPersistenceUnit"/&gt;

&lt;/beans&gt;</programlisting>

        <para>This action assumes standard Java EE 5 bootstrapping: the Java
        EE server autodetects persistence units (in effect,
        <literal>META-INF/persistence.xml</literal> files in application jars)
        and <literal>persistence-unit-ref</literal> entries in the Java EE
        deployment descriptor (for example, <literal>web.xml</literal>) and
        defines environment naming context locations for those persistence
        units.</para>

        <para>In such a scenario, the entire persistence unit deployment,
        including the weaving (byte-code transformation) of persistent
        classes, is up to the Java EE server. The JDBC
        <interfacename>DataSource</interfacename> is defined through a JNDI
        location in the <literal>META-INF/persistence.xml</literal> file;
        EntityManager transactions are integrated with the server's JTA
        subsystem. Spring merely uses the obtained
        <interfacename>EntityManagerFactory</interfacename>, passing it on to
        application objects through dependency injection, and managing
        transactions for the persistence unit,<!--identify *it* TR: REVISED, PLS REVIEW. Added *persistence unit*-->
        typically through <classname>JtaTransactionManager</classname>.</para>

        <para>If multiple persistence units are used in the same application,
        the bean names of such JNDI-retrieved persistence units should match
        the persistence unit names that the application uses to refer to them,
        for example, in <literal>@PersistenceUnit</literal> and
        <literal>@PersistenceContext</literal> annotations.</para>
      </section>

      <section xml:id="orm-jpa-setup-lcemfb">
        <title><classname>LocalContainerEntityManagerFactoryBean</classname></title>

        <note>
          <para>Use this option for full JPA capabilities in a Spring-based
          application environment. This includes web containers such as Tomcat
          as well as stand-alone applications and integration tests with
          sophisticated persistence requirements.</para>
        </note>

        <para>The
        <classname>LocalContainerEntityManagerFactoryBean</classname> gives
        full control over <interfacename>EntityManagerFactory</interfacename>
        configuration and is appropriate for environments where fine-grained
        customization is required. The
        <classname>LocalContainerEntityManagerFactoryBean</classname> creates
        a <interfacename>PersistenceUnitInfo</interfacename> instance based
        on the <literal>persistence.xml</literal> file, the supplied
        <literal>dataSourceLookup</literal> strategy, and the specified
        <literal>loadTimeWeaver</literal>. It is thus possible to work with
        custom data sources outside of JNDI and to control the weaving
        process. The following example shows a typical bean definition for a
        <interfacename>LocalContainerEntityManagerFactoryBean</interfacename>:<!--The following examples shows what? What's its purpose? TR: REVISED, PLS REVIEW.--></para>

        <programlisting language="xml">&lt;beans&gt;

 &lt;bean id="myEmf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"&gt;
  &lt;property name="dataSource" ref="someDataSource"/&gt;
  &lt;property name="loadTimeWeaver"&gt;
    &lt;bean class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver"/&gt;
  &lt;/property&gt;
 &lt;/bean&gt;

&lt;/beans&gt;</programlisting>

        <para>The following example shows a typical
        <literal>persistence.xml</literal> file:</para>

        <programlisting language="xml">&lt;persistence xmlns="http://java.sun.com/xml/ns/persistence" version="1.0"&gt;

  &lt;persistence-unit name="myUnit" transaction-type="RESOURCE_LOCAL"&gt;
    &lt;mapping-file&gt;META-INF/orm.xml&lt;/mapping-file&gt;
    &lt;exclude-unlisted-classes/&gt;
  &lt;/persistence-unit&gt;

&lt;/persistence&gt;</programlisting>

        <note>
          <para>The <code>exclude-unlisted-classes</code> element always
          indicates that <emphasis>no</emphasis> scanning for annotated entity
          classes is supposed to occur, in order to support the
          <code>&lt;exclude-unlisted-classes/&gt;</code> shortcut. This is in
          line with the JPA specification, which suggests that shortcut, but
          unfortunately is in conflict with the JPA XSD, which implies
          <code>false</code> for that shortcut. Consequently,
          <code>&lt;exclude-unlisted-classes&gt; false
          &lt;/exclude-unlisted-classes/&gt;</code> is not supported. Simply
          omit the <code>exclude-unlisted-classes</code> element if you want
          entity class scanning to occur.</para>
        </note>

        <para>Using the
        <classname>LocalContainerEntityManagerFactoryBean</classname> is the
        most powerful JPA setup option, allowing for flexible local
        configuration within the application. It supports links to an existing
        JDBC <interfacename>DataSource</interfacename>, supports both local
        and global transactions, and so on. However, it also imposes
        requirements on the runtime environment, such as the availability <!--Clarify: first says it imposes *requirements* but says such as *the availability* of a weaving-capable Classloader. Revise to say--><!--whether you are *required* to use this when persistence provider demands byte-code transformation. i.e. what is the *requirement* here?
TR: OK AS IS. The requirement is to provide the classloader for the runtime environment, if necessary - this is configured outside of Spring.-->of
        a weaving-capable class loader if the persistence provider demands
        byte-code transformation.</para>

        <para>This option may conflict with the built-in JPA capabilities of a
        Java EE 5 server. In a full Java EE 5 environment, consider obtaining
        your <interfacename>EntityManagerFactory</interfacename> from JNDI.
        Alternatively, specify a custom
        <classname>persistenceXmlLocation</classname> on your
        <classname>LocalContainerEntityManagerFactoryBean</classname>
        definition, for example, META-INF/my-persistence.xml, and only include
        a descriptor with that name in your application jar files. Because the
        Java EE 5 server only looks for default
        <literal>META-INF/persistence.xml</literal> files, it ignores such
        custom persistence units and hence avoid conflicts with a
        Spring-driven JPA setup upfront. (This applies to Resin 3.1, for
        example.)</para>

        <sidebar>
          <title>When is load-time weaving required?</title>

          <para>Not all JPA providers require a JVM agent ; Hibernate is an
          example of one that does not. If your provider does not require an
          agent or you have other alternatives, such as applying enhancements
          at build time through a custom compiler or an ant task, the
          load-time weaver <emphasis role="bold">should not</emphasis> be
          used.</para>
        </sidebar>

        <para>The <interfacename>LoadTimeWeaver</interfacename> interface is a
        Spring-provided class that allows JPA
        <interfacename>ClassTransformer</interfacename> instances to be
        plugged in a specific manner, depending whether the environment is a
        web container or application server. <!--Preceding: is this what you mean? Avoid slashes (web container/application server); slashes mean different things depending on context.--><!--Revise if necessary. TR: OK.-->
        Hooking <literal>ClassTransformers</literal> through a Java 5 <link
        xl:href="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/instrument/package-summary.html">agent</link>
        typically is not efficient. The agents work against the
        <emphasis>entire virtual machine</emphasis> and inspect
        <emphasis>every</emphasis> class that is loaded, which is usually
        undesirable in a production server environment.</para>

        <para>Spring provides a number of
        <interfacename>LoadTimeWeaver</interfacename> implementations for
        various environments, allowing
        <interfacename>ClassTransformer</interfacename> instances to be
        applied only <emphasis>per class loader</emphasis> and not per
        VM.</para>

        <para>Refer to <xref linkend="aop-aj-ltw-spring" /> in the AOP chapter for more insight regarding the
        <interfacename>LoadTimeWeaver</interfacename> implementations and their setup, either generic or customized to
        various platforms (such as Tomcat, WebLogic, GlassFish, Resin and JBoss).</para>


        <para>As described in the aforementioned section, you can configure a context-wide <interfacename>LoadTimeWeaver</interfacename>
        using the <interfacename>@EnableLoadTimeWeaving</interfacename> annotation of <literal>context:load-time-weaver</literal> XML element.
        Such a global weaver is picked up by all JPA <classname>LocalContainerEntityManagerFactoryBeans</classname>
        automatically. This is the preferred way of setting up a load-time weaver, delivering autodetection of the platform
        (WebLogic, GlassFish, Tomcat, Resin, JBoss or VM agent) and automatic propagation of the weaver to all weaver-aware beans:</para>

        <programlisting language="xml">&lt;context:load-time-weaver/&gt;
&lt;bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"&gt;
    ...
&lt;/bean&gt;</programlisting>

        <para> However, if needed, one can manually specify a dedicated weaver through the <literal>loadTimeWeaver</literal> property:</para>

        <programlisting language="xml">&lt;bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"&gt;
  &lt;property name="loadTimeWeaver"&gt;
    &lt;bean class="org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver"/&gt;
  &lt;/property&gt;
&lt;/bean&gt;</programlisting>

          <para>No matter how the LTW is configured, using this technique, JPA applications relying on
          instrumentation can run in the target platform (ex: Tomcat) without needing an agent.
          This is important especially when the hosting applications rely on different JPA implementations
          because the JPA transformers are applied only at class loader level and thus are
          isolated from each other.</para>

        <!--
          <note>
            <para>If you use TopLink Essentials as a JPA provider under
            Tomcat, place the toplink-essentials JAR under
            <emphasis>$CATALINA_HOME</emphasis>/shared/lib folder instead of
            inside your war.--><!--Revise: *instead of placing the JAR under your WAR*, OR *instead of placing WAR under $CATALINA_HOME/etc*?
TR: REVISED, PLS REVIEW. Should be *inside your war*. --><!-- </para>
          </note>
         -->
      </section>

      <section xml:id="orm-jpa-multiple-pu">
        <title>Dealing with multiple persistence units</title>

        <para>For applications that rely on multiple persistence units
        locations, stored in various JARS in the classpath, for example,
        Spring offers the
        <interfacename>PersistenceUnitManager</interfacename> to act as a
        central repository and to avoid the persistence units discovery
        process, which can be expensive. The default implementation allows
        multiple locations to be specified that are parsed and later retrieved
        through the persistence unit name. (By default, the classpath is
        searched for <filename>META-INF/persistence.xml</filename>
        files.)</para>

        <programlisting language="xml">&lt;bean id="pum" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager"&gt;
  &lt;property name="persistenceXmlLocations"&gt;
    &lt;list&gt;
     &lt;value&gt;org/springframework/orm/jpa/domain/persistence-multi.xml&lt;/value&gt;
     &lt;value&gt;classpath:/my/package/**/custom-persistence.xml&lt;/value&gt;
     &lt;value&gt;classpath*:META-INF/persistence.xml&lt;/value&gt;
    &lt;/list&gt;
  &lt;/property&gt;
  &lt;property name="dataSources"&gt;
   &lt;map&gt;
    &lt;entry key="localDataSource" value-ref="local-db"/&gt;
    &lt;entry key="remoteDataSource" value-ref="remote-db"/&gt;
   &lt;/map&gt;
  &lt;/property&gt;
  <lineannotation>&lt;!-- if no datasource is specified, use this one --&gt;</lineannotation>
  &lt;property name="defaultDataSource" ref="remoteDataSource"/&gt;
&lt;/bean&gt;

&lt;bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"&gt;
  &lt;property name="persistenceUnitManager" ref="pum"/&gt;
  &lt;property name="persistenceUnitName" value="myCustomUnit"/&gt;
&lt;/bean&gt;</programlisting>

        <para>The default implementation allows customization of the
        <interfacename>PersistenceUnitInfo</interfacename> instances,<!--What is *infos*? information? Clarify. TR: REVISED, PLS REVIEW.-->
        before they are fed to the JPA provider, declaratively through its
        <!--through what's properties? JPA provider's? TR: OK AS IS. It's the PersistenceUnitManager default implementation's properties-->properties,
        which affect <emphasis>all</emphasis> hosted units, or
        programmatically, through the
        <interfacename>PersistenceUnitPostProcessor</interfacename>, which
        allows persistence unit selection. If no
        <interfacename>PersistenceUnitManager</interfacename> is specified,
        one is created and used internally by
        <classname>LocalContainerEntityManagerFactoryBean</classname>.</para>
      </section>
    </section>

    <section xml:id="orm-jpa-straight">
      <title>Implementing DAOs based on plain JPA</title>

      <note>
        <para>Although <interfacename>EntityManagerFactory</interfacename>
        instances are thread-safe,
        <interfacename>EntityManager</interfacename> instances are not. The
        injected JPA <interfacename>EntityManager</interfacename> behaves like
        an <interfacename>EntityManager</interfacename> fetched from an
        application server's JNDI environment, as defined by the JPA
        specification. It delegates all calls to the current transactional
        <interfacename>EntityManager</interfacename>, if any; otherwise, it
        falls back to a newly created
        <interfacename>EntityManager</interfacename> per operation, in effect
        making its usage thread-safe.<!--Seems contradictory. First sentence says EntityManager instances are not thread-safe; last sentence refers to use--><!--of EntityManager as thread-safe. TR: REVISED, PLS REVIEW.--></para>
      </note>

      <para>It is possible to write code against the plain JPA without any
      Spring dependencies, by using an injected
      <interfacename>EntityManagerFactory</interfacename> or
      <interfacename>EntityManager</interfacename>. Spring can understand
      <interfacename>@PersistenceUnit</interfacename> and
      <interfacename>@PersistenceContext</interfacename> annotations both at
      field and method level if a
      <classname>PersistenceAnnotationBeanPostProcessor</classname> is
      enabled. A plain JPA DAO implementation using the
      <interfacename>@PersistenceUnit</interfacename> annotation <!--corresponding to what? TR: REVISED, PLS REVIEW.-->might
      look like this:</para>

      <programlisting language="java">public class ProductDaoImpl implements ProductDao {

    private EntityManagerFactory emf;

    @PersistenceUnit
    public void setEntityManagerFactory(EntityManagerFactory emf) {
        this.emf = emf;
    }

    public Collection loadProductsByCategory(String category) {
        EntityManager em = this.emf.createEntityManager();
        try {
             Query query = em.createQuery("from Product as p where p.category = ?1");
             query.setParameter(1, category);
             return query.getResultList();
        }
        finally {
            if (em != null) {
                em.close();
            }
        }
    }
}</programlisting>

      <para>The DAO above has no dependency on Spring and still fits nicely
      into a Spring application context. Moreover, the DAO takes advantage of
      annotations to require the injection of the default
      <interfacename>EntityManagerFactory</interfacename>:</para>

      <programlisting language="xml">&lt;beans&gt;

  <lineannotation>&lt;!-- bean post-processor for JPA annotations --&gt;</lineannotation>
  &lt;bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"/&gt;

&lt;/beans&gt;</programlisting>

      <para>As an alternative to defining a
      <classname>PersistenceAnnotationBeanPostProcessor</classname>
      explicitly, consider using the Spring
      <literal>context:annotation-config</literal> XML element in your
      application context configuration. Doing so automatically registers all
      Spring standard post-processors for annotation-based configuration,
      including <classname>CommonAnnotationBeanPostProcessor</classname> and
      so on.</para>

      <programlisting language="xml">&lt;beans&gt;

  <lineannotation>&lt;!-- post-processors for all standard config annotations --&gt;</lineannotation>
  &lt;context:annotation-config/&gt;

  &lt;bean id="myProductDao" class="product.ProductDaoImpl"/&gt;

&lt;/beans&gt;</programlisting>

      <para>The main problem with such a DAO is that it always creates a new
      <interfacename>EntityManager</interfacename> through the factory. You
      can avoid this by requesting a transactional
      <interfacename>EntityManager</interfacename> (also called "shared
      EntityManager" because it is a shared, thread-safe proxy for the actual
      transactional EntityManager) to be injected instead of the
      factory:</para>

      <programlisting language="java">public class ProductDaoImpl implements ProductDao {

    @PersistenceContext
    private EntityManager em;

    public Collection loadProductsByCategory(String category) {
       Query query = em.createQuery("from Product as p where p.category = :category");
       query.setParameter("category", category);
       return query.getResultList();
    }
}</programlisting>

      <para>The <literal>@PersistenceContext</literal> annotation has an
      optional attribute <literal>type</literal>, which defaults to
      <literal>PersistenceContextType.TRANSACTION</literal>. This default is
      what you need to receive a shared EntityManager proxy. The alternative,
      <literal>PersistenceContextType.EXTENDED</literal>, is a completely
      different affair: This results in a so-called extended EntityManager,
      which is <emphasis>not thread-safe</emphasis> and hence must not be used
      in a concurrently accessed component such as a Spring-managed singleton
      bean. Extended EntityManagers are only supposed to be used in stateful
      components that, for example, reside in a session, with the lifecycle of
      the EntityManager not tied to a current transaction but rather being
      completely up to the application.</para>

      <sidebar>
        <title>Method- and field-level Injection</title>

        <para>Annotations that indicate dependency injections (such as
        <literal>@PersistenceUnit</literal> and
        <literal>@PersistenceContext</literal>) can be applied on field or
        methods inside a class, hence the expressions <emphasis>method-level
        injection</emphasis> and <emphasis>field-level injection</emphasis>.
        Field-level annotations are concise and easier to use while
        method-level allows for further processing of the injected dependency.
        In both cases the member visibility (public, protected, private) does
        not matter.</para>

        <para>What about class-level annotations?</para>

        <para>On the Java EE 5 platform, they are used for dependency
        declaration and not for resource injection.</para>
      </sidebar>

      <para>The injected <interfacename>EntityManager</interfacename> is
      Spring-managed (aware of the ongoing transaction). It is important to
      note that even though the new DAO implementation uses method level
      injection of an <interfacename>EntityManager</interfacename> instead of
      an <interfacename>EntityManagerFactory</interfacename>, no change is
      required in the application context XML due to annotation usage.<!--I changed *prefers* to *works better with*. Revise if needed, but an impl. doesn't *prefer*. Also *what* is due to annotation usage; what does--><!--this refer to? TR: REVISED, PLS REVIEW.--></para>

      <para>The main advantage of this DAO style is that it only depends on
      Java Persistence API; no import of any Spring class is required.
      Moreover, as the JPA annotations are understood, the injections are
      applied automatically by the Spring container. This is appealing from a
      non-invasiveness perspective, and might feel more natural to JPA
      developers.</para>
    </section>

    <section xml:id="orm-jpa-tx">
      <title>Transaction Management</title>

      <note>
        <para>You are <emphasis>strongly</emphasis> encouraged to read <xref
        linkend="transaction-declarative" /> if you have not done so, to get a
        more detailed coverage of Spring's declarative transaction
        support.</para>
      </note>

      <para>To execute service operations within transactions, you can use
      Spring's common declarative transaction facilities. For example:</para>

      <programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop.xsd"&gt;

  &lt;bean id="myTxManager" class="org.springframework.orm.jpa.JpaTransactionManager"&gt;
    &lt;property name="entityManagerFactory" ref="myEmf"/&gt;
  &lt;/bean&gt;

  &lt;bean id="myProductService" class="product.ProductServiceImpl"&gt;
    &lt;property name="productDao" ref="myProductDao"/&gt;
  &lt;/bean&gt;

  &lt;aop:config&gt;
    &lt;aop:pointcut id="productServiceMethods" expression="execution(* product.ProductService.*(..))"/&gt;
    &lt;aop:advisor advice-ref="txAdvice" pointcut-ref="productServiceMethods"/&gt;
  &lt;/aop:config&gt;

  &lt;tx:advice id="txAdvice" transaction-manager="myTxManager"&gt;
    &lt;tx:attributes&gt;
      &lt;tx:method name="increasePrice*" propagation="REQUIRED"/&gt;
      &lt;tx:method name="someOtherBusinessMethod" propagation="REQUIRES_NEW"/&gt;
      &lt;tx:method name="*" propagation="SUPPORTS" read-only="true"/&gt;
    &lt;/tx:attributes&gt;
  &lt;/tx:advice&gt;

&lt;/beans&gt;</programlisting>

      <para>Spring JPA allows a configured
      <classname>JpaTransactionManager</classname> to expose a JPA transaction
      to JDBC access code that accesses the same JDBC
      <interfacename>DataSource</interfacename>, provided that the registered
      <interfacename>JpaDialect</interfacename> supports retrieval of the
      underlying JDBC <interfacename>Connection</interfacename>. Out of the
      box, Spring provides dialects for the Toplink, Hibernate and OpenJPA JPA
      implementations. See the next section for details on the
      <interfacename>JpaDialect</interfacename> mechanism.</para>
    </section>

    <section xml:id="orm-jpa-dialect">
      <title><interfacename>JpaDialect</interfacename></title>

      <para>As an advanced feature <classname>JpaTemplate</classname>,
      <classname>JpaTransactionManager</classname> and subclasses of
      <classname>AbstractEntityManagerFactoryBean</classname> support a custom
      <interfacename>JpaDialect</interfacename>, to be passed into the
      <property>jpaDialect</property> bean property. In such a scenario, the
      DAOs do not receive an
      <interfacename>EntityManagerFactory</interfacename> reference but rather
      a full <classname>JpaTemplate</classname> instance (for example,
      passed<!--Clarify *what* is passed? Reword this for example phrase. TR: OK AS-->
      into the <property>jpaTemplate</property> property<classname> of
      JpaDaoSupport</classname>). A <interfacename>JpaDialect</interfacename>
      implementation can enable some advanced features supported by Spring,
      usually in a vendor-specific manner:</para>

      <itemizedlist>
        <listitem>
          <para>Applying specific transaction semantics such as custom
          isolation level or transaction timeout)</para>
        </listitem>

        <listitem>
          <para>Retrieving the transactional JDBC
          <interfacename>Connection</interfacename> for exposure to JDBC-based
          DAOs)</para>
        </listitem>

        <listitem>
          <para>Advanced translation of
          <literal>PersistenceExceptions</literal> to Spring
          <literal>DataAccessExceptions</literal></para>
        </listitem>
      </itemizedlist>

      <para>This is particularly valuable for special transaction semantics
      and for advanced translation of exception. The default implementation
      used (<classname>DefaultJpaDialect</classname>) does not provide any
      special capabilities and if the above features are required, you have to
      specify the appropriate dialect.</para>

      <para>See the <interfacename>JpaDialect</interfacename> Javadoc for more
      details of its operations and how they are used within Spring's JPA
      support.</para>
    </section>
  </section>

</chapter>
