Java 动态更改持久性单元 - JPA
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Changing Persistence Unit dynamically - JPA
提问by N K
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.
persistence.xml 中的持久性单元是在构建应用程序期间创建的。由于我想在运行时更改数据库 url，有没有办法在运行时修改持久性单元？我应该在分发后使用不同的数据库而不是预先绑定的数据库。
I'm using EclipseLink (JPA 2.1)
我正在使用 EclipseLink (JPA 2.1)
采纳答案by N K
Keep the persistence unit file (Persistence.xml) as it's. You can override the properties in it as follows.
保持持久性单元文件 (Persistence.xml) 不变。您可以按如下方式覆盖其中的属性。
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by Grim
In Long-lived Session Architecture you should create a Plug-in-Framework.
在长寿命会话架构中，您应该创建一个插件框架。
Therefore you need to create a different Thread-Group and Class-Repository.
因此，您需要创建不同的线程组和类存储库。
This might be your Class-Loader-Tree
这可能是你的类加载器树
- System-Class-Loader (usually a URLClassLoader, contains the Entitys)
- JPA-Class-Loader
- Load your jpa.jarwith
persistence.xmlinside, 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.
- Load your jpa.jarwith
- JPA-Class-Loader
- System-Class-Loader（通常是 URLClassLoader，包含实体）
- JPA-Class-Loader
- 用里面加载你的jpa.jar，
persistence.xml从 Application-Class-Loader 中指定 Database-Configuration - 实例化您的 entityManager/session-factory。
- 加载使用数据库所需的任何插件。执行单元测试 (;D) 和插件集成测试。
- 用里面加载你的jpa.jar，
- JPA-Class-Loader
回答by James
You can use Persistence.createEntityManagerFactory(Map) to pass properties to choose the database URL and other settings.
您可以使用 Persistence.createEntityManagerFactory(Map) 传递属性来选择数据库 URL 和其他设置。
