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：

<form action="servlet/LoginServlet" method="post">
    	<table>
    		<tr>
    			<td>用户账号：</td>
    			<td><input type="text" name="username" onblur="checkUser(this)"/></td>
    		</tr>
    		<tr>
    			<td>用户密码：</td>
    			<td><input type="password" name="password"/></td>
    		</tr>
    		<tr>
    			<td><input type="submit" value="注冊"/></td>
    			<td><input type="reset" value="重置"></td>
    		</tr>
    	</table>
    </form>

然后看对发送信息进行处理的Servlet类。由于是POST方式发送信息，所以看一下doPost方法。

@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();
	}

然后看javascript怎样实现Ajax请求

"); 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>