CuriousMind CuriousMind - 1 year ago 88
Java Question

property tags in persistence.xml when using JPA

I am new to JPA and use Hibernate as the JPA provider. I came to know that we need

configuration file.

I successfully created a simple Java program to persist data in DB using JPA.

All fine, doubts started when I looked into the
file to understand it better.

Sample below:

<persistence-unit name="test-jpa" transaction-type="RESOURCE_LOCAL">
<property name="hibernate.connection.driver_class" value="org.h2.Driver"/>
<property name="hibernate.connection.url" value="jdbc:h2:tcp://localhost/~/test"/>
<property name="hibernate.connection.username" value="sa" />
<property name="hibernate.connection.password" value="" />
<property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
<property name="" value="create" />
<property name="hibernate.show_sql" value="true" />

The following is the Java code for reading the configuration:

EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("test-jpa");

The following are the doubts:

  1. How do we know that Hibernate is the JPA provider? Is it inferred by seeing the property tags in the file?

  2. In config file, there are many
    tags, are they pre-defined which can appear in the file (for a given JPA provider) or can we randomly add any property? who reads those

Answer Source

A JPA provider would provide documentation that would tell you all of that. Doesn't yours? I'd be surprised.

  1. You should either have a <provider> element in the persistence-unit to define which provider to use, or it would use the default for the environment that you are running in (in JavaSE you would need to have 1 and only one JPA provider in the CLASSPATH, in JavaEE the server would have its own default).

  2. They are provider-specific. Any properties that are prefixed javax.persistence would be JPA STANDARD. The first 4 of those posted have javax.persistence variants that you should have used instead.

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