json是一种与语言无关的数据交换的格式，作用：
使用ajax进行前后台数据交换
移动端与服务端的数据交换
1．Json的格式与解析
json有两种格式：
1）对象格式：{"key1":obj,"key2":obj,"key3":obj...}
2）数组/集合格式：[obj,obj,obj...]
例如：user对象 用json数据格式表示
{"username":"zhangsan","age":28,"password":"123","addr":"北京"}
List<Product> 用json数据格式表示
[{"pid":"10","pname":"小米4C"},{},{}]
注意：对象格式和数组格式可以互相嵌套
注意：json的key是字符串 json的value是Object
json的解析：
json是js的原生内容，也就意味着js可以直接取出json对象中的数据
如下：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>insertBefore.html</title>
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="this is my page">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<!--<link rel="stylesheet" type="text/css" href="./styles.css">-->
</head>
<body>
<ul>
<li id="bj" name="beijing">北京</li>
</ul>
</body>
<script language="JavaScript">
/**
* 案例五
* {
* "param1":"value1",
* "param2":{},
* "param3":[{key:value,key:value},{key:value,key:value}]
* }
*
*
*/
var json = {
"key1":"value1",
"key2":{"firstname":"张","lastname":"三丰","age":100},
"key3":[
{"name":"小双","age":28,"addr":"扬州"},
{"name":"建宁","age":18,"addr":"紫禁城"},
{"name":"阿珂","age":10,"addr":"山西"},
]
};
alert(json.key2.lastname);
alert(json.key3[2].name);
</script>
</html>