Java Persistence/Spring

Spring is an application framework for Java. Spring is an IoC container that allows for a different programming model. Spring is similar to a JEE server, in that it provides a transaction service, XML deployment, annotation processing, byte-code weaving, and JPA integration.

Persistence

Persistence in Spring in normally done through a DAO (Data Access Object) layer. The Spring DAO layer is meant to encapsulate the persistence mechanism, so the same application data access API would be given no matter if JDBC, JPA or a native API were used.

Spring also defines a transaction manager implementation that is similar to JTA. Spring also supports transactional annotations and beans similar to SessionBeans.

JPA

Spring has specific support for JPA and can emulate some of the functionality of a JEE container with respect to JPA. Spring allows a JPA persistence unit to be deployed in container managed mode. If the spring-agent is used to start the JVM, Spring can deploy a JPA persistence unit with weaving similar to a JEE server. Spring can also pass a Spring DataSource and integrate its transaction service with JPA. Spring allows the @PersistenceUnit and @PersistenceContext annotations to be used in any Spring bean class, to have an EntityManager or EntityManagerFactory injected. Spring supports a managed transactional EntityManager similar to JEE, where the EntityManager binds itself as a new persistence context to each new transaction and commits as part of the transaction. Spring supports both JTA integration, and its own transaction manager.

Example Spring JPA Deployment

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
  			http://www.springframework.org/schema/beans
    		http://www.springframework.org/schema/beans/spring-beans-2.0.xsd">

    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="persistenceUnitName" value="acme" />
        <property name="persistenceUnitManager" ref="persistenceUnitManager" />
    </bean>

    <bean id="persistenceUnitManager" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager">
        <property name="defaultDataSource" ref="dataSource" />
        <property name="dataSources">
            <map>
                <entry>
                    <key>
                        <value>jdbc/__default</value>
                    </key>
                    <ref bean="dataSource" />
                </entry>
                <entry>
                    <key>
                        <value>jdbc/jta</value>
                    </key>
                    <ref bean="dataSource" />
                </entry>
            </map>
        </property>
        <property name="loadTimeWeaver">
            <bean class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver" />
        </property>
    </bean>

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="oracle.jdbc.OracleDriver" />
        <property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl" />
        <property name="username" value="scott" />
        <property name="password" value="tiger" />
    </bean>

    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>
    
    <bean id="entityManager" class="org.springframework.orm.jpa.support.SharedEntityManagerBean">
        <property name="entityManagerFactory" ref="entityManagerFactory"/>
    </bean>

    <bean id="AcmeDao" class="org.acme.dao.AcmeDao">
        <property name="entityManager" ref="entityManager" />
    </bean>

</beans>