为什么不调用PostConstruct？ [英] Why is PostConstruct not called?

问题描述

我正在开发一个简单的Java EE应用程序。

我有这样的类：

  import javax.annotation.PostConstruct; 
 import javax.ejb.Stateless; 
 import javax.persistence.EntityManager; 
 import javax.persistence.EntityManagerFactory; 
 import javax.persistence.Persistence; 
 
 @Stateless 
 public class BlogEntryDao {
 
 EntityManager em; 
 
 @PostConstruct 
 public void initialize（）{
 EntityManagerFactory emf = Persistence.createEntityManagerFactory（Persistence）; 
 em = emf.createEntityManager（）; 
} 
 
 public void addNewEntry（）{
 Blogentry blogentry = new Blogentry（）; 
 
 blogentry.setTitle（Test）; 
 blogentry.setContent（asdfasfas）; 
 
 em.persist（blogentry）; 
 
} 
} 
  

所以我的托管bean调用这个方法。直到这里没有问题。但是，由于初始化方法没有被调用，所以我在 em.persist 中得到一个NPE。

为什么初始化方法不被调用？我在Glassfish服务器上运行这个。

请问。

解决方案

Java EE bean注释（如 @PostConstruct ）仅适用于容器管理的bean。如果您自己简单地调用新的BlogEntryDao ，容器将不会拦截创建，并调用 @PostConstruct 方法。

（此外，您最好使用 @PersistenceContext 或 @ PersistenceUnit 而不是在您的 initialize（）方法中手动获取 EntityManagerFactory ，而应该为每次调用 addNewEntry（）创建一个 EntityManager ，因为它们是短暂的，进行这些更改消除对 initialize（）的需要。）

I am working on a simple Java EE application.

I have class like this:

import javax.annotation.PostConstruct;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

@Stateless
public class BlogEntryDao {

    EntityManager em;

    @PostConstruct
    public void initialize(){
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("Persistence");
        em = emf.createEntityManager();
    }

    public void addNewEntry(){
        Blogentry blogentry = new Blogentry();

        blogentry.setTitle("Test");
        blogentry.setContent("asdfasfas");

        em.persist(blogentry);

    }
}

So my managed bean calls this method. Until here no problems. But since the initialize method is not called, I am getting an NPE in em.persist.

Why is the initialize method not being called? I am running this on Glassfish server.

Regards.

解决方案

The Java EE bean annotations such as @PostConstruct only apply to container-managed beans. If you are simply calling new BlogEntryDao yourself, the container isn't going to intercept the creation and call the @PostConstruct method.

(Furthermore, you'd be better off using @PersistenceContext or @PersistenceUnit instead of manually fetching the EntityManagerFactory in your initialize() method, and you should be creating an EntityManager for each call to addNewEntry(), since they're short-lived. Making these changes would eliminate the need for initialize() at all.)

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