/**
　* Destruction of the servlet. <br>
　*/
　public void destroy() {
　super.destroy(); // Just puts "destroy" string in log
　// Put your code here
　}

/**
　* The doGet method of the servlet. <br>
　*
　* This method is called when a form has its tag value method equals to get.
　*
　* @param request the request send by the client to the server
　* @param response the response send by the server to the client
　* @throws ServletException if an error oclearcase/" target="_blank" >ccurred
　* @throws IOException if an error occurred
　*/
　public void doGet(HttpServletRequest request， HttpServletResponse response)
　throws ServletException， IOException {
　response.setContentType("text/xml");
　response.setHeader("Cache-Control"， "no-cache");

String targetId = request.getParameter("id");
　System.out.println(targetId.trim());

if ((targetId != null) && users.containsKey(targetId.trim())) {

response.getWriter().write("<info><message>welcome</message><name>sdl</name></info>");
　} else {

response.getWriter().write("<info><message>kill</message><name>bush</name></info>");
　System.out.print("invalid");
　}

}

　/**
　* Initialization of the servlet. <br>
　*
　* @throws ServletException if an error occure
　*/
　public void init(ServletConfig config) throws ServletException {
　this.context = config.getServletContext();
　users.put("greg"，"account data");
　users.put("duke"，"account data");

}

}
　
　[3]写web.xml文件<?xml version="1.0" encoding="UTF-8"?>
　<web-app version="2.4"
　xmlns="http://java.sun.com/xml/ns/j2ee "
　xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance "
　xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
　http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
　<servlet>
　<description>This is the description of my J2EE component</description>
　<display-name>This is the display name of my J2EE component</display-name>
　<servlet-name>ValidateServlet</servlet-name>
　<servlet-class>com.ValidateServlet</servlet-class>
　</servlet>

<servlet-mapping>
　<servlet-name>ValidateServlet</servlet-name>
　<url-pattern>/servlet/ValidateServlet</url-pattern>
　</servlet-mapping>

</web-app>
　
　[4]说明：
　你可以在IE或FireFox里测试，在文本输入框里输入，当按键抬起，会在层中显示”kill you bush”。其中index.htm中的styles.css只是美化页面，没有列出来源代码。如果在servlet向客户端输出中文，需要编码转换。

　[多此一举]
　你需要了解tomcat工程。熟悉xmlHttpRequest，java servlet，html等知识。