ajax实现异步刷新

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://"
            + request.getServerName() + ":" + request.getServerPort()
            + path + "/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
    <head>
        <base href="<%=basePath%>">

        <title>My JSP 'login.jsp' starting page</title>

        <meta http-equiv="pragma" content="no-cache">
        <meta http-equiv="cache-control" content="no-cache">
        <meta http-equiv="expires" content="0">
        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
        <meta http-equiv="description" content="This is my page">
        <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

        <script type="text/javascript" src="js/jquery-1.8.3.js">
</script>
    </head>
    <script type="text/javascript">
方法一

function chkName() {
    var name = $("#username").val();
    //alert(name);

    $.ajax( {
        url : "server.jsp",
        data : "name=" + name, //发送数据
        dataType : "text", //响应数据类型
        type : "get", //请求发方式
        success : function(value) {  //成功之后
            if ($.trim(value) == "true") {
                $("#msg").html("用户已存在！");
            } else {
                $("#msg").html("此用户可用！");
            }
        }
    });
}

</script>
方法二

方法三

方法四




    <body>
        <form action="login.action" method="post">
            <div>
                用户名：
                <input name="username" type="text" value="" id="username"
                    onblur="chkName()" />
                <span id="msg"></span>
            </div>

            <input type="submit" value="提交" />
        </form>
    </body>
</html>

server.jsp

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

<%
   String name=request.getParameter("name");
   if("sa".equals(name)){
     out.print("true");
   }else{
     out.print("false");
   }

%>