OpenJPA first looks for an optional openjpa.xml resource. OpenJPA searches for this resource in each top-level directory of your CLASSPATH. OpenJPA will also find the resource if you place it within a META-INF directory in any top-level directory of the CLASSPATH. The openjpa.xml resource contains property settings in JPA's XML format.

You can customize the name or location of the above resource by specifying the correct resource path in the openjpa.properties System property.

You can override any value defined in the above resource by setting the System property of the same name to the desired value.

In JPA, the values in the standard META-INF/persistence.xml bootstrapping file used by the Persistence class at runtime override the values in the above resource, as well as any System property settings. The Map passed to Persistence.createEntityManagerFactory at runtime also overrides previous settings, including properties defined in persistence.xml.

When using JCA deployment the config-property values in your ra.xml file override other settings.

All OpenJPA command-line tools accept flags that allow you to specify the configuration resource to use, and to override any property. Section 3, “ Command Line Configuration ” describes these flags.