如何创建一个线程安全的EntityManagerFactory？

问题描述

我正在开发一个需要进行一些数据库操作的应用程序。

I'm working on a application that needs to do some database operations.

我为EntityManagerFactory创建了一个静态变量，并在被调用的方法中对其进行了初始化应用程序

I created a static variable for EntityManagerFactory and Intialized it in the method that gets called by the application

 if (emf == null){
                    emf = Persistence.createEntityManagerFactory("example");
                }

try {
            em = emf.createEntityManager();
        } catch (Exception ex) {
            logger.error(ex.getMessage());
        }

这个线程安全吗？如果我在同步块中创建EntityManagerFactory，等待线程的数量会增加并使应用程序崩溃。

is this thread safe? if I create the EntityManagerFactory in a synchronized block, The number of waiting threads increases and crashes the application.

我查看了文档以查看Persistence.createEntityManagerFactory是否是线程保证没有任何成功。

I looked at the docs to see whether the Persistence.createEntityManagerFactory is thread safe without any success.

请指出正确的资源。

推荐答案

解决这个问题的简单方法是使用辅助类（la HibernateUtil ）并初始化 EntityManagerFactory 在静态初始化块中。这样的事情：

An easy way to "solve" this would be to use a helper class (a la HibernateUtil) and to initialize the EntityManagerFactory in a static initialization block. Something like this:

public class JpaUtil {
    private static final EntityManagerFactory emf;

    static {
        try {
            factory = Persistence.createEntityManagerFactory("MyPu");
        } catch (Throwable ex) {
            logger.error("Initial SessionFactory creation failed", ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

   ...

}

而且问题消失了。

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