如何从过滤器确定 RequestDispatcher.forward 调用转发到哪个 jsp？

Question

我有一个过滤器，用于处理请求以记录它们，因此我可以跟踪哪个会话在什么时间使用什么请求参数访问页面。效果很好...从 jsp 发送到 jsp，或者直接调用 jsp。但是，当将表单发布到 servlet 并将该请求转发到新的 jsp 时，我无法看到该请求被转发到哪个 jsp。

例如，假设我有一个登录页面，它发布到 LoginServlet，然后将请求转发到 index.jsp 或 index1.jsp。如何从请求中确定 LoginServlet 返回的是 index.jsp 还是 index1.jsp？

这是在使用 2.3 servlet 规范的 java 1.5 环境中。

public class PageLogFilter implements Filter {

    FilterConfig filterConfig = null;

    public void init(FilterConfig filterConfig) throws ServletException {
        this.filterConfig = filterConfig;
    }

    public void destroy() {
        this.filterConfig = null;
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        try {
            if (request instanceof HttpServletRequest) {
                HttpServletRequest req = (HttpServletRequest) request;
                HttpSession session = req.getSession(false);

                //For non-forwards, I can call req.getRequestURI() to determine which 
                //page was returned. For forwards, it returns me the URI of the  
                //servlet which processed the post. I'd like to also get the URI
                //of the jsp to which the request was forwarded by the servlet, for
                //example "index.jsp" or "index1.jsp"
            }
        } catch (Exception e {
            System.out.println("-- ERROR IN PageLogFilter: " + e.getLocalizedMessage());
        }

        chain.doFilter(request, response);
    }
}

Answer 1

如果您同意执行额外检查，则可以使用属性来设置/获取原始请求 URI。
在您的 LoginServlet 中设置属性：

//LoginServlet
public void doFilter(...) {
      HttpServletRequest oReq = (HttpServletRequest)request;
      ..
      ...
      //save original request URI
      oReq.setAttribute("originalUri", oReq.getRequestURI());
}

并在您的 PageLogFilter 中检查originalUri 属性是否有值，然后将该值视为请求 URI

//PageLogFilter 
public void doFilter(...) {
      HttpServletRequest req = (HttpServletRequest) request;
      if(req.getAttribute("originalUri") != null) {
          String strOriginalUri = (String) req.getAttribute("originalUri");
          //set it back to null
      req.setAttribute("originalUri", null);
      }
}

Answer 2

虽然它不能帮助解决您眼前的问题，但 Servlet 2.4 添加了对调度程序的更详细的控制，这正是您想要的。

使用它，您可以配置过滤器以添加以下调度程序元素，这将导致过滤器也适用于转发。

<filter-mapping>
       <filter-name>PageLogFilter</filter-name>
       <url-pattern>/*</url-pattern>
       <dispatcher>FORWARD</dispatcher>
</filter-mapping>

以下文章更详细地解释了它

http://www.ibm.com/ developerworks/java/library/j-tomcat2/