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 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 jaon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

    <script language="JavaScript">
        //案例一
        var person = {"firstname":"张","lastname":"三丰","age":100};

        //取出lastname对象
        alert(person.lastname);
        //取出age
        alert(person.age);
        //案例二
        var persons = [
            {"firstname":"张","lastname":"三丰","age":100},
            {"firstname":"李","lastname":"三丰","age":200}
        ];
        alert(persons[1].firstname);
        //案例三
        var json = {
            "baobao":[
                {"name":"小双","age":28,"addr":"扬州"},
                {"name":"静宁","age":28,"addr":"扬州"},
                {"name":"珂珂","age":28,"addr":"扬州"}
            ]
        };
        alert(json.baobao[1].name);
        //案例四
        var jsons = {
            "baobao":[
                {"name":"小双","age":28,"addr":"扬州"},
                {"name":"静宁","age":28,"addr":"扬州"},
                {"name":"珂珂","age":28,"addr":"扬州"}
            ],
            "haohao":[
                {"name":"小双","age":28,"addr":"扬州"},
                {"name":"静宁","age":28,"addr":"扬州"},
                {"name":"珂珂","age":28,"addr":"扬州"}
            ]
        };
        alert(json.baobao[1].name);
    </script>