Servlet获取URL地址。在HttpServletRequest类里，有以下六个取URL的函数：

getContextPath 取得项目名 getServletPath 取得Servlet名 getPathInfo 取得Servlet后的URL名，不包括URL参数 getRequestURL 取得不包括参数的URL getRequestURI 取得不包括参数的URI，即去掉协议和服务器名的URL

相对应的函数的值如下：

getContextPath：/ServletTest getServletPath：/main getPathInfo：/index/testpage/test getRequestURL：http://localhost:8080/ServletTest/main/index/testpage/test getRequestURI：/ServletTest/main/index/testpage/test

验证用户名

package com.glut.demo;import java.io.IOException;import java.util.Arrays;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ValidateUserName extends HttpServlet {        private static final long serialVersionUID = 1L;    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        System.out.println("aa");        List
    
      usernames = Arrays.asList("AAA","BBB","CCC");        String username = request.getParameter("username");        System.out.println("aa");        String result = null;        if(usernames.contains(username)){            result = "
     该用户名已经被使用";        }else{            result = "
     该用户名可以使用";        }        response.setContentType("text/html");        response.getWriter().print(result);    }}
    

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>          
                           
    
         Username: