在哪里声明具有多个服务的 JDO Singleton PersistenceManagerFactory

发布于 2024-08-29 10:29:30 字数 1004 浏览 5 评论 0原文

我正在使用 GWT，并且有 4 个需要 PersistenceManagerFactory 的服务实现。我遵循了 Google 关于创建单例类的建议，但是我不确定应该在服务器端代码中的何处实例化和引用该类。

该类看起来像这样

import javax.jdo.JDOHelper;
import javax.jdo.PersistenceManagerFactory;

public final class PMF {
    private static final PersistenceManagerFactory pmfInstance =
        JDOHelper.getPersistenceManagerFactory("transactions-optional");

    private PMF() {}

    public static PersistenceManagerFactory get() {
        return pmfInstance;
    }
}

但是在每个服务实现中执行类似的操作似乎最终会根据我收到的错误消息创建单例的唯一副本“应用程序代码试图创建一个名为 transactions-Optional 的 PersistenceManagerFactory，但具有此名称已经存在了！”

@Override
 public void addCategory(Category category) {
  PersistenceManager pm = PMF.get().getPersistenceManager();
  try {
        pm.makePersistent(category);
  } finally {
       pm.close();
     }
 }

所以基本上第一个调用 addCategory 的 ServiceImpl 没问题，所有其他的都失败并出现上述错误。我在这里遗漏了一些重要的东西，我认为单例类的全部要点是创建一个静态 PersistenceManagerFactory。非常感谢任何对我所缺少的内容的见解。

原文

I am working with GWT and have 4 Service Implementations that need a PersistenceManagerFactory. I followed Google's advice on creating a singleton class, however I am unsure of where this class should be instantiated and referenced from in the server-side code.

The class looks like this

import javax.jdo.JDOHelper;
import javax.jdo.PersistenceManagerFactory;

public final class PMF {
    private static final PersistenceManagerFactory pmfInstance =
        JDOHelper.getPersistenceManagerFactory("transactions-optional");

    private PMF() {}

    public static PersistenceManagerFactory get() {
        return pmfInstance;
    }
}

But doing something like this in each Service Implementation seems to end up creating a unique copy of the singleton based on the error message I get "Application code attempted to create a PersistenceManagerFactory named transactions-optional, but one with this name already exists!"

@Override
 public void addCategory(Category category) {
  PersistenceManager pm = PMF.get().getPersistenceManager();
  try {
        pm.makePersistent(category);
  } finally {
       pm.close();
     }
 }

So basically the first ServiceImpl that calls addCategory is fine, all others fail with the error above. I am missing something vital here, I thought the whole point of the singleton class is to create a static PersistenceManagerFactory. Any insights into what I am missing are greatly appreciated.

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