1．Java代码如下:
 packagecom.eduask;
 importjava.io.IOException;
 importjava.util.Date;
 importjavax.servlet.ServletException;
 importjavax.servlet.http.HttpServlet;
 importjavax.servlet.http.HttpServletRequest;
 importjavax.servlet.http.HttpServletResponse;
 publicclassDemo4extendsHttpServlet {
 @Override
 protectedvoidservice(HttpServletRequest req, HttpServletResponse resp)
 throwsServletException, IOException {
 req.setCharacterEncoding("utf-8");
 resp.setCharacterEncoding("utf-8");
 resp.setContentType("text/xml;charset=utf-8");
 String name=req.getParameter("name1");
 if("tom".equals(name)) {
 resp.getWriter().write("<root>abc"+"<msg>"+"用户名不可以注册"+"</msg>"+"</root>");
 }else{
 resp.getWriter().write("<root>abc"+"<msg>"+"用户名可以注册"+"</msg>"+"</root>");
 }
 
 }
 }
 2.xmldemo4.jsp代码如下：
 <body>
 请输入用户名: <input id="name1"type="text"name="name1">
 <span id="span1"></span>
 <script type="text/javascript">
 vargetName1Id=document.getElementById("name1");
 getName1Id.οnblur=function(){
 varxhr=getXhr();
 xhr.onreadystatechange=function(){
 if(xhr.readyState==4){
 if(xhr.status==200){
 vardoc=xhr.responseXML;
 vare1=doc.getElementsByTagName("msg")[0];
 varmsg=e1.firstChild.nodeValue;
 //alert(msg);
 varspan=document.getElementById("span1");
 span.innerHTML="<font color=red>"+msg+"</font>";
 }
 }
 }
 xhr.open("post","/ajax/Demo4");
 //设置消息头，告诉浏览器携带请求体数据;
 xhr.setRequestHeader("content-type","application/x-www-form-urlencoded");
 varspan=document.getElementById("span1");
 span.innerHTML="正在加载数据"
 xhr.send("name1="+getName1Id.value);
 }
 functiongetXhr(){
 varxhr;
 if(window.XMLHttpRequest){
 xhr=newXMLHttpRequest();
 }else{
 xhr=newActiveXObject("microsoft,xmlhttp");
 }
 returnxhr;
 }
 </script>
 </body>
 3.web.xml配置文件如下:
 <!-- demo4 -->
 <servlet>
 <servlet-name>Demo4</servlet-name>
 <servlet-class>com.eduask.Demo4</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>Demo4</servlet-name>
 <url-pattern>/Demo4</url-pattern>
 </servlet-mapping>