Using Spring+Hibernate for testing purposes

EntityManagerFactory will obtain java.sql.Connection objects, through opening/closing new physical connections to the database or using a connection pool (c3p0, bonecp, hikari or whatever implementation you like). After obtaining a Connection, it will use it to create a new EntityManager. The EntityManager can interact with your objects and your database using this Connection and can manage the transaction through calling EntityManager#getTransaction and then calling EntityTransaction#begin, EntityTransaction#commit and EntityTransaction#rollback that internally works with Connection#begin, Connection#commit and Connection#rollback respectively. This is plain vanilla JPA and Spring has nothing to do up to this point.

For transaction management, Spring helps you to avoid opening/closing the transactions manually by using a transaction manager, specifically a class called JpaTransactionManager. This transaction manager will make use of your EntityManagerFactory to open and close a transaction for the EntityManager created for a set of operations. This can be done either using XML configuration or @Transactional annotation on your classes/methods. When using this approach, you won't directly work with your specific classes anymore, instead Spring will create proxies for your classes using cglib and make use of the transaction manager class to open the transaction, call your specific method(s) and execute a commit or rollback at the end, depending on your configuration. Apart of this, Spring provides other configurations like read-only transactions (no data modification operation allowed).

Here's a basic configuration of the elements explained above using Spring/Hibernate/JPA:

<!--
    Declare the datasource.
    Look for your datasource provider like c3p0 or HikariCP.
    Using most basic parameters. It's up to you to tune this config.
-->
<bean id="jpaDataSource"
    class="..."
    destroy-method="close"
    driverClass="${app.jdbc.driverClassName}"
    jdbcUrl="${app.jdbc.url}"
    user="${app.jdbc.username}"
    password="${app.jdbc.password}" />

<!--
    Specify the ORM vendor. This is, the framework implementing JPA.
-->
<bean id="hibernateVendor"
    class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"
    showSql="false"/>

<!--
    Declare the JPA EntityManagerFactory.
    Spring provides a class implementation for it.
-->
<bean id="entityManagerFactory"
    class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
    persistenceXmlLocation="classpath*:META-INF/persistence.xml"
    persistenceUnitName="hibernatePersistenceUnit"
    dataSource-ref="jpaDataSource"
    jpaVendorAdapter-ref="hibernateVendor"/>

<!--
    Declare a transaction manager.
    Spring uses the transaction manager on top of EntityManagerFactory.
-->
<bean id="transactionManager"
    class="org.springframework.orm.jpa.JpaTransactionManager"
    entityManagerFactory-ref="entityManagerFactory"/>