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在不断重复这些行之后，Tomcat 给了我 StackOverflowError，DiceBoardDispatcher我的 HttpServlet 在哪里，我在第 34 行调用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：

  <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>

我想做的是让两个动作都登陆同一页面。我以为我会这样设置。每个动作都经过自己的Filter处理，它们都以Servlet分派到JSP.

我的 url-patter 映射曾经是 to /diceBoard/*，它是 web-app 中某处的文件夹。从那里改变到去/dices/*时解决问题url/dices。现在我可以正常访问该页面，但是当url/dices/roll我进入无限循环时（无论是 POST 还是 GET）。

编辑：我的 servlet 代码：

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：

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() { }
}
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1 回答 1

3

这是您的错误所在的行：

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

根据getRequestDispatcher API，输入 uri 是相对于当前 servlet 上下文的，所以当你在执行你的 servlet 时

/dices/roll

...并且它执行对“diceBoardPage.jsp”的调度，它实际上是调度到

/dices/diceBoardPage.jsp

这个模式映射到什么 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。

如果 JSP 必须保留在dicesuri 中，则必须限制映射DiceBoardservlet 的 URL 模式。如果需要，请毫不犹豫地添加几个值：

<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>
于 2018-01-31T19:46:33.057 回答