Java 如何从servlet中访问相应servlet过滤器中的变量集？

我想使用以下过滤器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() {}
}

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我不知道如何从相应的servlet内部访问

manager

变量，该servlet在此筛选器之后被调用。

在筛选器中，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：

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