1、看到上面的黑体字了吗？哪里就是出现该错误的原因。Caused by: java.lang.IllegalArgumentException: The servlets named [helloworld] and [HelloWorld] are both mapped to the url-pattern [/HelloWorld] which is not permitted at org.apache.tomcat.util.descriptor.web.WebXml.addServletMapping(WebXml.java:308)
2、Servlet的时候eclipse已经帮助建好了url-patten。@WebServlet("/HelloWorld")public class HelloWorld extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public HelloWorld() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doPost(request,response); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub String u_name=request.getParameter("u_name"); String ad="Welcome,"+u_name; request.setAttribute("ad", ad); request.getRequestDispatcher("/welcome.jsp").forward(request, response); }}
3、打开你的Servlet类，你会发现在类上面有一个@WebServlet("/HelloWorld")。如果你在web.xml里面这样写：<servlet> <servlet-name>helloworld</servlet-name> <servlet-class>HelloWorld</servlet-class> </servlet> <servlet-mapping> <servlet-name>helloworld</servlet-name> <url-pattern>/HelloWorld</url-pattern></servlet-mapping>就是报错。
4、解决方法一：去掉类上面的@WebServlet("/HelloWorld")。在web.xml写<servlet-mapping>。
5、解决方法二：在web.xml里不写 <servlet-mapping>,而要保留@WebServlet("/HelloWorld")。如下web.xml:<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1"> <display-name>HelloWorld</display-name> <welcome-file-list> <welcome-file>index.html</welcome-file> </welcome-file-list> <servlet> <servlet-name>helloworld</servlet-name> <servlet-class>HelloWorld</servlet-class> </servlet></web-app>