Ajax发送post请求与发送get请求大致类似。以下看详细实例。首先看JSP显示页面：

    
    	
     
    		      
       
    			        
用户账号：
    			        
    		       
    		       
    			        
用户密码：
    			        
    		       
    		       
    			        
    			        
    		       
    	      
     
    
    

@Override	protected void doPost(HttpServletRequest request, HttpServletResponse response)			throws ServletException, IOException {				response.setContentType("text/html;charaet=UTF-8");		PrintWriter out = response.getWriter();		String name=request.getParameter("username");		if(name.equals("admin"))			out.print(false);		else			out.print(true);		out.flush();		out.close();	}

"); obj.focus(); return; } //不为空时。使用Ajax请求向后台发送信息，验证该username是否可用 //post请求字符串 var url="servlet/LoginServlet"; //请求參数 var userinfo = "username="+user; //调用方法创建XMLHttpRequest对象 XmlHttpRequest = createXmlHttpRequest(); //设置回调函数 XmlHttpRequest.onreadystatechange=finish; //初始化xmlhttprequest XmlHttpRequest.open("POST",url,true); XmlHttpRequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); //发送请求 XmlHttpRequest.send(userinfo); } //回调函数 function finish(){ if(XmlHttpRequest.readyState == 4&& XmlHttpRequest.status == 200){ var result = XmlHttpRequest.responseText; alert(result); if(result =="true"){ alert("username可用！"); }else{ alert("username不可用！"); } } } </script>