Persistence.xml file in JPA

Persistence.xml 

How will JPA API (EntityManager)  come to know which database to connect, connection parameters,transaction types,logging level etc.? Persistence.xml is a standard configuration file which gives complete flexibility to configure EntityManager

Persistence.xml :-

1. is to be created under META-INF/persistence.xml
2. A persistence.xml can contain one or more unique persistence unit names
3. Persistence units are unique values used by EntityManagerFactory/Entitymanager
4. Entities ,Connection parameters,logging level ,transaction types etc are declared in persistence.xml

EntityManagerFactory emf =Persistence.createEntityManagerFactory("JPAExample_Toplink");

The following persistence.xml defines one persistence unit with name JPAExample_Toplink

<persistence version="2.0"

xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

<persistence-unit name="JPAExample_Toplink"

transaction-type="RESOURCE_LOCAL">

<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>

<class>model.Company</class>

<class>model.Department</class>

<class>model.DeptEmpl</class>

<properties>

<property name="javax.persistence.jdbc.password" value="admin" />

<property name="javax.persistence.jdbc.user" value="system" />

<property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver" />

<property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@localhost:1521:XE" />

<property name="eclipselink.logging.level" value="INFO" />

<property name="eclipselink.ddl-generation" value="create-tables" />

</properties>

</persistence-unit>

</persistence>

Eclipse automatically creates persistence.xml file when we create a JPA project.It also provides an persistence xml file editor which reduces the manual effort of writing the file.

We can edit :-

Connection

Managed classes

mapping files

Query timeouts

                         Happy Learning

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