如何堆叠在Java中的自定义批注与@Inject注解

问题描述

我浏览..人都在用 @Inject 标注自己的注入，当看到这几次的EntityManager 像这样的：

I saw this several times when browsing.. people are using @Inject annotation with their own to inject EntityManager like this:

@Inject @MyEm EnityManager em;

因为你不能仅仅注入的EntityManager 。您只能使用 @PersistenceContext 做到这一点。是否有人知道如何使这项工作（与自定义注释），因为我没有在网络上找到任何信息？如果你可以给一个例子，请。

because you cannot just inject the EntityManager. You can do it only with @PersistenceContext. Does anybody know how to make this work (with the custom annotation), because I didn't find any information on the net? Give a example if you can, please.

推荐答案

基本上你需要做的是建立一个鉴别注释和结合生产者使用方法。这使您可以在您的Java EE应用程序中的其他Bean简单@Inject你的实体管理器。下面是一个例子：

Basically what you need to do is create a discriminator annotation and use it in conjunction with a Producer. This allows you to simple @Inject your Entity Manager in other beans within your Java EE application. Here is an example:

@Qualifier
@Retention(RUNTIME)
@Target(METHOD, FIELD, PARAMETER, TYPE)
public interface @MyEm {
}

public class EntityProducer {
    @PersistenceContext(unitName = 'MyPU', type = PersistenceContextType.EXTENDED)
    private EntityManager entityManager;

    @Produces
    @MyEm
    public EntityManager getEntityManager() {
        return entityManager;
    }
}

public class MyDAO {
    @Inject
    @MyEm
    private EntityManager entityManager;
}

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