Tomcat在requestDispatcher#forward()上无限循环. StackOverflowError [英] Tomcat infinte loop on requestDispatcher#forward(). StackOverflowError

问题描述

Tomcat不断重复这些行之后就给了我StackOverflowError，其中DiceBoardDispatcher是我的HttpServlet，在第34行中，我正在调用requestDispatcher#forward().

Tomcat is giving me StackOverflowError after constantly repeating these lines, where DiceBoardDispatcher is my HttpServlet and in line 34 I am calling requestDispatcher#forward().

nl.rickhurkens.rollDice.web.diceBoard.DiceBoardDispatcher.doGet(DiceBoardDispatcher.java:34)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
        nl.rickhurkens.rollDice.web.diceBoard.DiceBoardDispatcher.doGet(DiceBoardDispatcher.java:34)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

我想这与我的部署有关，这是我的web.xml的相关部分:

I guess it's got something to do with my deployment, here is the relevant part of my web.xml:

  <servlet-mapping>
    <servlet-name>DiceBoard</servlet-name>
    <url-pattern>/dices/*</url-pattern>
  </servlet-mapping>

  <filter-mapping>
    <filter-name>RollDiceFilter</filter-name>
    <url-pattern>/dices/roll</url-pattern>
  </filter-mapping>
  <filter-mapping>
    <filter-name>SetSettingsFilter</filter-name>
    <url-pattern>/dices/setup</url-pattern>
  </filter-mapping>

我要执行的操作是在同一页面上同时执行2个操作.我以为我会这样设置.每个动作都经过自己的Filter，它们都以Servlet结尾，而该Servlet分派给JSP.

What I am trying to do is have 2 actions both landing on the same page. I thought I'd set it up like this. Each action goes through its own Filter and they both end in the Servlet that dispatches to a JSP.

我的url-pattern映射曾经是/diceBoard/*，它是Web应用程序中的某个文件夹.从那里更改为/dices/*可以解决转到url/dices时的问题.现在，我可以正常访问该页面了，但是当进入url/dices/roll时，我会遇到无限循环(无论是POST还是GET).

My url-patter mapping used to be to /diceBoard/*, which is a folder somewhere in the web-app. Changing from there to /dices/* fixed the problem when going to url/dices. Now I can reach that page normally, but when going to url/dices/roll I get the infinite loop (no matter if POST or GET).

我的servlet代码:

My servlet code:

public class DiceBoardDispatcher extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        RequestDispatcher view = request.getRequestDispatcher("diceBoardPage.jsp");
        view.forward(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        RequestDispatcher view = request.getRequestDispatcher("diceBoardPage.jsp");
        view.forward(request, response);
    }
}

和RollDiceFilter:

And RollDiceFilter:

public class RollDiceFilter implements Filter {
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse res = (HttpServletResponse)response;
        HttpSession session = req.getSession();

        DiceBoard diceBoard = (DiceBoard)session.getAttribute("diceBoard");
        String[] lockedValues = req.getParameterValues("lock");

        diceBoard.unlockAllDice();
        if (lockedValues != null) {
            for (String value : lockedValues) {
                if (value != null) {
                    try {
                        diceBoard.lockDice(Integer.parseInt(value));
                    } catch (DiceNotInCollectionException e) {
                        // TODO: redirect to error page.
                        e.printStackTrace();
                    }
                }
            }
        }
        diceBoard.getCup().roll();

        chain.doFilter(req, res);
    }

    public void init(FilterConfig fConfig) throws ServletException { }
    public void destroy() { }
}

推荐答案

这是您的错误所在的行:

This is the line where your error is located:

RequestDispatcher view = request.getRequestDispatcher("diceBoardPage.jsp");

根据 getRequestDispatcher API ，输入uri是相对于当前servlet上下文的 ，因此，当您在

According to the getRequestDispatcher API, the input uri is relative to the current servlet context, so when you are executing your servlet at

/dices/roll

...并且它执行对"diceBoardPage.jsp"的分派，实际上是在分派给

... and it performs a dispatch to "diceBoardPage.jsp", it is actually dispatching to

/dices/diceBoardPage.jsp

该模式映射到哪个servlet?根据您的部署描述符，每个以"/dices/*"开头的URL都映射到DiceBoard. IE.相同的servlet.这是导致您的StackOverflowError的无限循环.

And what servlet is mapped this pattern to? According to your deployment descriptor, every URL beginning with "/dices/*" is mapped to DiceBoard. I.E. the same servlet. Here comes the infinite loop that caused your StackOverflowError.

如果JSP必须保留在dices uri内，则必须限制映射DiceBoard servlet的URL模式.如果需要，请不要犹豫添加几个值:

If the JSP must stay within the dices uri, you must restrict the URL pattern which maps the DiceBoard servlet. Do not hesitate to add several values if needed:

<servlet-mapping>
    <servlet-name>DiceBoard</servlet-name>
    <url-pattern>/dices/one</url-pattern>
    <url-pattern>/dices/two</url-pattern>
    <url-pattern>/dices/three</url-pattern>
</servlet-mapping>

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