Changing Persistence Unit dynamically - JPA

问题:

Persistence units in persistence.xml are created during building the application. As I want to change the database url at runtime, is there any way to modify the persistence unit at runtime? I supposed to use different database other than pre-binded one after distributed.

I'm using EclipseLink (JPA 2.1)

回答1:

Keep the persistence unit file (Persistence.xml) as it's. You can override the properties in it as follows.

EntityManagerFactory managerFactory = null;
Map<String, String> persistenceMap = new HashMap<String, String>();

persistenceMap.put("javax.persistence.jdbc.url", "<url>");
persistenceMap.put("javax.persistence.jdbc.user", "<username>");
persistenceMap.put("javax.persistence.jdbc.password", "<password>");
persistenceMap.put("javax.persistence.jdbc.driver", "<driver>");

managerFactory = Persistence.createEntityManagerFactory("<current persistence unit>", persistenceMap);
manager = managerFactory.createEntityManager();

回答2:

You can use Persistence.createEntityManagerFactory(Map) to pass properties to choose the database URL and other settings.

回答3:

In Long-lived Session Architecture you should create a Plug-in-Framework.

Therefore you need to create a different Thread-Group and Class-Repository.

This might be your Class-Loader-Tree

• System-Class-Loader (usually a URLClassLoader, contains the Entitys)
  • JPA-Class-Loader
    • Load your jpa.jar with persistence.xml inside, specify the Database-Configuration from Application-Class-Loader
    • Instanciate your entityManager/session-factory.
    • Load any plugin you need to work with the DataBase. Execute Unit-Tests (;D) and Plugin-Integration-Tests.