如何从 servlet 中访问相应 servlet 过滤器中的变量集？

Posted 2023-02-26

【中文标题】如何从 servlet 中访问相应 servlet 过滤器中的变量集？

【英文标题】：From within a servlet how do you access a variable set inside a corresponding servlet filter?

【发布时间】：2011-04-14 19:16:34

【问题描述】：

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。

【参考方案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");