如何使用@Inject 注释在 Java 中堆叠自定义注释 [英] How to stack custom annotation in Java with @Inject annotation

问题描述

我在浏览时多次看到这个..人们使用 @Inject 注释和他们自己的注入 EntityManager 像这样:

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

@Inject @MyEm EnityManager em;  

因为你不能只注入 EntityManager.您只能使用 @PersistenceContext 来完成.有没有人知道如何使这项工作(使用自定义注释)，因为我没有在网上找到任何信息?如果可以，请举个例子.

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，您需要做的是创建一个鉴别器注释并将其与 Producer 结合使用.这允许您在 Java EE 应用程序中的其他 bean 中简单地 @Inject 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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