google-app-engine - 如何在 Google App Engine 上的同一个 RPC 请求中始终使用同一个 PersistenceManager

Question

有没有办法确保在同一 RPC 请求的上下文中执行的不同代码部分中使用相同的 PersistenceManager 实例？

不得不手动处理从一个函数到另一个函数的持久性管理器实例是相当痛苦的：

例如：

private void updateItem(ItemModel listItem)
        throws UserNotLoggedInException {
   PersistenceManager pm = PMF.get().getPersistenceManager();
   if (isItemIsNew(pm, listItem)) { 
        workOnItem(pm, listItem);
   }
   workSomeMoreOnItem(pm, listItem);

}

Answer 1

Google Cookbook 提供以下答案：

使用过滤器，您可以使 PersistenceManager 可用并保证它在请求结束时关闭。如果您使用的是为您处理渲染的 MVC 框架，例如 Spring，那么这对于保持管理器打开足够长的时间以使 View 仍然能够获取尚未访问的持久对象也很有用。

public final class PersistenceFilter implements Filter {
    private static final PersistenceManagerFactory persistenceManagerFactory
        = JDOHelper.getPersistenceManagerFactory("transactions-optional");

    private static PersistenceManagerFactory factory() {
        return persistenceManagerFactory;
    }

    private static ThreadLocal currentManager = new ThreadLocal();

    public static PersistenceManager getManager() {
        if (currentManager.get() == null) {
            currentManager.set(factory().getPersistenceManager());
        }
        return currentManager.get();
    }
    @Override
    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {
        PersistenceManager manager  = null;
        try {
            manager = getManager();
            //Optional: allow all persistent objects implementing a custom interface
            //to be notified of when they are saved and loaded.
            manager.addInstanceLifecycleListener(new PersistHookListener(), PersistHooks.class);
            chain.doFilter(req, res);
        } finally {
            if (manager != null) {
                manager.flush();
                manager.close();
            }
        }
    }
    @Override
    public void init(FilterConfig arg0) throws ServletException {}
    @Override
    public void destroy() {}
}

http://appengine-cookbook.appspot.com/recipe/persistencefilter/?id=ahJhcHBlbmdpbmUtY29va2Jvb2tyigELEgtSZWNpcGVJbmRleCI2YWhKaGNIQmxibWRwYm1VdFkyOXZhMkp2YjJ0eUVnc1NDRU5oZEdWbmIzSjVJZ1JLWVhaaERBDAsSBlJlY2lwZSI3YWhKaGNIQmxibWRwYm1VdFkyOXZhMkp2YjJ0eUVnc1NDRU5oZEdWbmIzSjVJZ1JLWVhaaERBMAw