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| <chapter id="jpa_overview_arch"> |
| <title> |
| Java Persistence API Architecture |
| </title> |
| <indexterm zone="jpa_overview_arch"> |
| <primary> |
| JPA |
| </primary> |
| <secondary> |
| architecture |
| </secondary> |
| </indexterm> |
| <para> |
| The diagram below illustrates the relationships between the primary components |
| of the JPA architecture. |
| </para> |
| <mediaobject> |
| <imageobject> |
| <!-- PNG image data 400 x 256 (see README) --> |
| <imagedata fileref="img/jpa-arch.png" width="267px"/> |
| |
| </imageobject> |
| <textobject> |
| <phrase> |
| JPA architecture |
| </phrase> |
| </textobject> |
| </mediaobject> |
| <note> |
| <para> |
| A number of the depicted interfaces are only required outside of an |
| EJB3-compliant application server. In an application server, <classname> |
| EntityManager</classname> instances are typically injected, rendering the |
| <classname>EntityManagerFactory</classname> unnecessary. Also, transactions |
| within an application server are handled using standard application server |
| transaction controls. Thus, the <classname>EntityTransaction</classname> also |
| goes unused. |
| </para> |
| </note> |
| <itemizedlist> |
| <listitem> |
| <para> |
| <indexterm> |
| <primary> |
| Persistence |
| </primary> |
| </indexterm> |
| <emphasis role="bold"><link linkend="jpa_overview_persistence"><classname> |
| Persistence</classname></link></emphasis>: The <classname> |
| javax.persistence.Persistence</classname> class contains static helper methods |
| to obtain <classname>EntityManagerFactory</classname> instances in a |
| vendor-neutral fashion. |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <indexterm> |
| <primary> |
| EntityManagerFactory |
| </primary> |
| </indexterm> |
| <emphasis role="bold"><link linkend="jpa_overview_emfactory"><classname> |
| EntityManagerFactory</classname></link></emphasis>: The <classname> |
| javax.persistence.EntityManagerFactory</classname> class is a factory for |
| <classname> EntityManager</classname> s. |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <indexterm> |
| <primary> |
| EntityManager |
| </primary> |
| </indexterm> |
| <emphasis role="bold"><link linkend="jpa_overview_em"><classname>EntityManager |
| </classname></link></emphasis>: The <classname>javax.persistence.EntityManager |
| </classname> is the primary JPA interface used by applications. Each |
| <classname>EntityManager</classname> manages a set of persistent objects, and |
| has APIs to insert new objects and delete existing ones. When used outside the |
| container, there is a one-to-one relationship between an <classname> |
| EntityManager</classname> and an <classname> EntityTransaction</classname>. |
| <classname> EntityManager</classname>s also act as factories for <classname> |
| Query</classname> instances. |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <indexterm> |
| <primary> |
| entity |
| </primary> |
| </indexterm> |
| <emphasis role="bold"><link linkend="jpa_overview_pc"><classname>Entity |
| </classname></link></emphasis>: Entities are persistent objects that represent |
| datastore records. |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <indexterm> |
| <primary> |
| EntityTransaction |
| </primary> |
| </indexterm> |
| <emphasis role="bold"><link linkend="jpa_overview_trans"><classname> |
| EntityTransaction</classname></link></emphasis>: Each <classname>EntityManager |
| </classname> has a one-to-one relation with a single <classname> |
| javax.persistence.EntityTransaction</classname>. <classname> |
| EntityTransaction</classname>s allow operations on persistent data to be |
| grouped into units of work that either completely succeed or completely fail, |
| leaving the datastore in its original state. These all-or-nothing operations |
| are important for maintaining data integrity. |
| </para> |
| </listitem> |
| <listitem> |
| <para> |
| <indexterm> |
| <primary> |
| Query |
| </primary> |
| </indexterm> |
| <indexterm> |
| <primary> |
| Java Persistence Query Language |
| </primary> |
| <see> |
| JPQL |
| </see> |
| </indexterm> |
| <indexterm> |
| <primary> |
| JPQL |
| </primary> |
| </indexterm> |
| <indexterm> |
| <primary> |
| JPA |
| </primary> |
| <secondary> |
| query language |
| </secondary> |
| <see> |
| JPQL |
| </see> |
| </indexterm> |
| <indexterm> |
| <primary> |
| Structured Query Language |
| </primary> |
| <see> |
| SQL |
| </see> |
| </indexterm> |
| <indexterm> |
| <primary> |
| SQL |
| </primary> |
| </indexterm> |
| <emphasis role="bold"><link linkend="jpa_overview_query"><classname>Query |
| </classname></link></emphasis>: The <classname>javax.persistence.Query |
| </classname> interface is implemented by each JPA vendor to find persistent |
| objects that meet certain criteria. JPA standardizes support for queries using |
| both the Java Persistence Query Language (JPQL) and the Structured Query |
| Language (SQL). You obtain <classname>Query</classname> instances from an |
| <classname>EntityManager</classname>. |
| </para> |
| </listitem> |
| </itemizedlist> |
| <para> |
| The example below illustrates how the JPA interfaces interact to execute a JPQL |
| query and update persistent objects. The example assumes execution outside a |
| container. |
| </para> |
| <example id="jpa_overview_arch_interact_outside"> |
| <title> |
| Interaction of Interfaces Outside Container |
| </title> |
| <programlisting> |
| // get an EntityManagerFactory using the Persistence class |
| // It is not recommended to obtain a factory often, as construction of a |
| // factory is a costly operation. Typically you will like to cache |
| // a factory and then refer it for repeated use |
| EntityManagerFactory factory = Persistence.createEntityManagerFactory(null); |
| |
| // get an EntityManager from the factory |
| EntityManager em = factory.createEntityManager(); |
| |
| // Begin a transaction |
| em.getTransaction().begin(); |
| |
| // query for all employees who work in our research division |
| // and put in over 40 hours a week average |
| Query query = em.createQuery("SELECT e " + |
| " FROM Employee e " + |
| " WHERE e.division.name = 'Research' " + |
| " AND e.avgHours > 40"); |
| List results = query.getResultList(); |
| |
| // give all those hard-working employees a raise |
| for (Object res : results) { |
| Employee emp = (Employee) res; |
| emp.setSalary(emp.getSalary() * 1.1); |
| } |
| |
| // commit will detect all updated entities and save them in database |
| em.getTransaction().commit(); |
| |
| // free the resources |
| em.close(); |
| </programlisting> |
| </example> |
| <para> |
| Within a container, the <classname>EntityManager</classname> will be injected |
| and transactions will be handled declaratively. Thus, the in-container version |
| of the example consists entirely of business logic: |
| </para> |
| <example id="jpa_overview_arch_interact_inside"> |
| <title> |
| Interaction of Interfaces Inside Container |
| </title> |
| <programlisting> |
| // query for all employees who work in our research division |
| // and put in over 40 hours a week average - note that the EntityManager em |
| // is injected using a @Resource annotation |
| Query query = em.createQuery("select e from Employee e where " |
| + "e.division.name = 'Research' and e.avgHours > 40"); |
| List results = query.getResultList(); |
| |
| // give all those hard-working employees a raise |
| for (Object res : results) { |
| emp = (Employee) res; |
| emp.setSalary(emp.getSalary() * 1.1); |
| } |
| </programlisting> |
| </example> |
| <para> |
| The remainder of this document explores the JPA interfaces in detail. We present |
| them in roughly the order that you will use them as you develop your |
| application. |
| </para> |
| <section id="jpa_overview_arch_exceptions"> |
| <title> |
| JPA Exceptions |
| </title> |
| <indexterm zone="jpa_overview_arch_exceptions"> |
| <primary> |
| JPA |
| </primary> |
| <secondary> |
| exceptions |
| </secondary> |
| <seealso> |
| exceptions |
| </seealso> |
| </indexterm> |
| <indexterm> |
| <primary> |
| exceptions |
| </primary> |
| <secondary> |
| JPA |
| </secondary> |
| </indexterm> |
| <mediaobject> |
| <imageobject> |
| <!-- PNG image data, 427 x 355 (see README) --> |
| <imagedata fileref="img/jpa-exceptions.png" width="285px"/> |
| |
| </imageobject> |
| <textobject> |
| <phrase> |
| JPA exception architecture |
| </phrase> |
| </textobject> |
| </mediaobject> |
| <para> |
| The diagram above depicts the JPA exception architecture. All |
| exceptions are unchecked. JPA uses standard exceptions where |
| appropriate, most notably <classname>IllegalArgumentException</classname>s and |
| <classname>IllegalStateException</classname>s. The specification also provides |
| a few JPA-specific exceptions in the <literal>javax.persistence</literal> |
| package. These exceptions should be self-explanatory. See the |
| <ulink url="http://download.oracle.com/javaee/6/api/">Javadoc</ulink> for |
| additional details on JPA exceptions. |
| </para> |
| <note> |
| <para> |
| All exceptions thrown by OpenJPA implement |
| <ulink url="../../apidocs/org/apache/openjpa/util/ExceptionInfo.html"><classname> |
| org.apache.openjpa.util.ExceptionInfo</classname></ulink> to provide you with |
| additional error information. |
| </para> |
| </note> |
| </section> |
| </chapter> |
