如何从 servlet 中访问相应 servlet 过滤器中的变量集？

Question

我想使用以下过滤器来打开和关闭持久性管理器。

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() {}
}

我不知道如何从在此过滤器之后调用的相应 servlet 内部访问 manager 变量。

Answer 1

在过滤器中，将管理器作为请求属性：

request.setAttribute("persistenceManager", manager);

然后，在 servlet 中，可以通过以下方式访问它：

PersistenceManager manager = 
     (PersistenceManager) request.getAttribute("persistenceManager");