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Persistence XML

A persistence unit is a named set of entities (instances of POJOs annotated with @Entity) in your application, and the mapping of those entities to the database (Entity -> SQL and SQL -> Entity).

You will define persistence units (we will only have one) in a persistence.xml file located in the src/main/resources/META-INF/ directory.

Declare the persistence unit name using the name attribute of the <persistence-unit> element.

<persistence-unit name="VideoStore">
  <!-- ... -->
</persistence-unit>
Identify which persistence provider you wish to use with the <provider> element (we are using Hibernate).

<persistence-unit name="VideoStore">
  <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
  <!-- ... -->
</persistence-unit>

Provide configuration information for the persistence unit using the <property> element.

<persistence-unit name="VideoStore">
  <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <!-- ... -->
  <properties>
    <property name="javax.persistence.jdbc.url"
            value="jdbc:mysql://localhost:3306/sdvid?useSSL=false" />
    <property name="javax.persistence.jdbc.user" value="student"/>
    <property name="javax.persistence.jdbc.password" value="student" />
    <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver" />
  </properties>

</persistence-unit>

Standard elements include:

  • url - the location of your database server.

  • user - the username to access your database server.

  • password - the password to access your database server.

  • driver - the driver class to use for connecting to your SQL implementation.

You can also add provider specific configuration here.

  • For Hibernate, there are debug configurables that can be toggled on and off to help you during development.

  • For c3p0, you can configure the connection pool settings, dictating the length of time until the pooled connections time out, and the maximum number of connections.

Drill

  1. If you don't already have one, create a persistence.xml file in the src/main/resources/META-INF directory.

  2. Use the template below for the basic elements of your file.

  3. Name the persistence unit VideoStore.

  4. Add additional properties to the file to specify database and connection pool information as below.

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2" xmlns="http://xmlns.jcp.org/xml/ns/persistence" 
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">
  <persistence-unit name="VideoStore">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider
    </provider>

    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/sdvid?useSSL=false&amp;useLegacyDatetimeCode=false&amp;serverTimezone=US/Mountain" />
      <property name="javax.persistence.jdbc.user" value="student"/>
      <property name="javax.persistence.jdbc.password" value="student" />
      <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver" />

      <property name="hibernate.show_sql" value="false" />
      <property name="hibernate.format_sql" value="false" />

      <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
      <property name="hibernate.connection.provider_class" value="org.hibernate.connection.C3P0ConnectionProvider" />

      <property name="hibernate.c3p0.max_size" value="5" />
      <property name="hibernate.c3p0.min_size" value="0" />
      <property name="hibernate.c3p0.acquire_increment" value="1" />
      <property name="hibernate.c3p0.idle_test_period" value="300"/>
      <property name="hibernate.c3p0.max_statements" value="0" />
      <property name="hibernate.c3p0.timeout" value="60" />
    </properties>
  </persistence-unit>
</persistence>

  1. Inside of src/main/resources/ create a file named log4j.properties.

  2. Add the following as its contents:

    // Logging levels, from least verbose to most, are:
// OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE, and ALL
// Change this line from WARN to INFO for more detailed logging
log4j.rootLogger=WARN, stdout
log4j.logger.org.hibernate.type=trace
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n

  3. Copy log4j.properties to src/test/resources/.

    In this copy, you might want to change log4j.logger.org.hibernate.type=trace to log4j.logger.org.hibernate.type=WARN to speed up and declutter the extensive unit testing you will be doing.

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