将实体管理器注入到托管bean中 [英] Injecting entity manager into managed bean

问题描述

是否可以使用@PersistenceContext(或@PersistenceUnit)将实体管理器(或其工厂)注入到jsf管理的bean中?

It is possible to inject entity manager (or its factory) into jsf managed bean using @PersistenceContext (or @PersistenceUnit)?

我尝试了一下，但是没有，我得到了NullPointerException.

I Tried it but nothing, I obtain a NullPointerException.

推荐答案

是可以的.这是语法.

@PersistenceContext
EntityManager em;

您的项目中需要有一个persistence.xml.顺便说一句:我正在运行Glassfish 3.

You need to have a persistence.xml in your project. Btw: I'm running Glassfish 3.

此后，您可以使用em.createNamedQuery之类的方法.

After this you can then use methods like em.createNamedQuery.

还请记住，注入是在构造函数之后进行的，因此，如果您尝试在构造函数中执行数据库功能，将无法正常工作.您必须将@PostConstruct批注添加到方法中.这可能是您遇到的问题.

Also remember the injection takes place after the constructor so if your trying to do database functions in the constructor this will not work. You will have to add the @PostConstruct annotation to a method. This is probably the problem your having.

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