java - 服务器遇到意外情况，无法满足请求。 HTTP 500

Question

我想对多个页面使用一个 servlet。当我尝试运行该项目时，由于请求已满而发生错误。尝试了多种 URL 模式选项，但没有结果

现在，我只看到一种方法。仅使用 post 方法并具有空的 url 模式，但我不确定这是正确的选择:D

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
  <display-name>Archetype Created Web Application</display-name>

  <session-config>
    <session-timeout>10</session-timeout>
  </session-config>

  <filter>
    <filter-name>InitialFilter</filter-name>
    <filter-class>eshop.filter.InitialFilter</filter-class>

    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>

  </filter>

  <filter>
  <filter-name>SessionFilter</filter-name>
  <filter-class>eshop.filter.SessionFilter</filter-class>
  </filter>

  <filter-mapping>
    <filter-name>InitialFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <filter-mapping>
    <filter-name>SessionFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <servlet>
    <servlet-name>mainServlet</servlet-name>
    <servlet-class>eshop.controller.MainServlet</servlet-class>
    <load-on-startup>0</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>mainServlet</servlet-name>
    <url-pattern>*.jsp</url-pattern>
  </servlet-mapping>

    <error-page>
        <location>/WEB-INF/views/error.jsp</location>
    </error-page>

</web-app>

    public class IndexCommand implements Command {

        @Override
        public void execute(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException, MessagingException, ServiceException, SQLException {
            if (request.getSession().getAttribute("role")=="admin")
            {
                Command command=new AccountCommand();
                command.execute(request,response);
            }
            System.out.println(request.getRequestURI());
            request.getRequestDispatcher("/WEB-INF/views/startPage.jsp").forward(request,response);
        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            Command command = CommandFactory.createCommand(request);
            try {
                command.execute(request, response);
            } catch (MessagingException e) {
                e.printStackTrace();
            } catch (SQLException e) {
                e.printStackTrace();
            } catch (ServiceException e) {
                e.printStackTrace();
            }

        }

    Type Exception Report

    Message Servlet execution threw an exception

    Description The server encountered an unexpected condition that prevented it from fulfilling the request.

    Exception

    javax.servlet.ServletException: Servlet execution threw an exception
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        eshop.command.IndexCommand.execute(IndexCommand.java:34)
        eshop.controller.MainServlet.doGet(MainServlet.java:62)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        eshop.command.IndexCommand.execute(IndexCommand.java:34)
        eshop.controller.MainServlet.doGet(MainServlet.java:62)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

    Root Cause

    java.lang.StackOverflowError
        eshop.command.IndexCommand.execute(IndexCommand.java:34)
        eshop.controller.MainServlet.doGet(MainServlet.java:62)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

如何配置 web.xml 以将 servlet 映射到 Java 中的多个 url 模式，问题出在哪里？

Answer 1

您可以为 servlet 添加任意数量的映射，但可以将它们作为单独的 serrvlet-mapping 元素放置。

 <servlet-mapping>
    <servlet-name>mainServlet</servlet-name>
    <url-pattern>*.jsp</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>mainServlet</servlet-name>
    <url-pattern>*.jsp</url-pattern>
  </servlet-mapping>

关于第二个问题，您会遇到无限循环，因为 JEE 过滤器也会在通过 RequestDispatcher 到您的 JSP 页面的内部调度中被触发。因此，当您尝试分派(dispatch)到 JSP 时，您会再次点击过滤器链中的第一个过滤器，并且在这里您会得到无限循环。因此您可以指定您的过滤器仅针对外部请求。

<filter-mapping>
  <filter-name>RequestLoggingFilter</filter-name> <!-- mandatory -->
  <url-pattern>/*</url-pattern>
  <servlet-name>XXXXXXXXXXXXXXXXX</servlet-name>
  <dispatcher>REQUEST</dispatcher>
</filter-mapping>

检查您的 WsFilter，它导致了问题，因为似乎所有过滤器都在/* 上触发。如果您发布完整的 web.xml，以便我知道出现的顺序，我可以为您提供更多帮助。

您可以阅读 Oracle 教程来过滤请求，这是了解这些内容的最佳教程。

https://docs.oracle.com/javaee/5/tutorial/doc/bnagb.html

我认为将逻辑放入过滤器中并不是一个好主意。好的设计是将逻辑放入 servlet 中。