java web-12.2JSON

JSON基本语法

1.概念
JavaScript Object Notation JavaScript对象表示法

Person p = new Person();
p.setName("张三");
p.setAge(23);
p.setGender("男")；
var p={"name":"张三","age":23,"gender":"男"}；

json现在多用于存储和交换文本信息的语法
进行数据的传输
JSON比xml更小，更快，更易解析
2.语法
（1）基本规则
①数据在名称/值对中：json数据是由键值对构成的
a.数字（整数或浮点数）
b.字符串（在双引号中）
c.逻辑值（true或false）
d.数组（在方括号中）{“persons”：[{},{}]}
e.对象（在花括号中）{“address”：{“province”：“陕西”…}}
f.null
②数据有逗号分隔：多个键值对由逗号分隔
③花括号保存对象：使用{}定义json格式
④方括号保存数组：[]
示例

<script>
        //1，定义基本格式
        var p = {"name":"战三",age:23,'gender':true};
        //alert(person);

        //2.嵌套格式{}->[]
        var person = {"persons":[
                {"name":"张三","age":23,"gender":true},
                {"name":"李四","age":24,"gender":false},
                {"name":"王五","age":25,"gender":true}]};
        alert(person);
        //3嵌套格式[]->{}
        var ps = [{"name":"张三","age":23,"gender":true},
            {"name":"李四","age":24,"gender":false},
            {"name":"王五","age":25,"gender":true}];

    </script>

（2）获取数据
a.json对象.键名
b.json对象[“键名”]
c.数组对象[索引]
示例

<script>
        //1，定义基本格式
        var p = {"name":"战三",age:23,'gender':true};
        //获取name的值
        //var name = p.name;
        var name = p["name"];
        alert(name)
        //2.嵌套格式{}->[]
        var person = {
            "persons":[
                {"name":"张三","age":23,"gender":true},
                {"name":"李四","age":24,"gender":false},
                {"name":"王五","age":25,"gender":true}
                ]};
        //获取王五的值
        var name1 = person.persons[2].name;
        alert(name1)

        //3嵌套格式[]->{}
        var ps = [{"name":"张三","age":23,"gender":true},
            {"name":"李四","age":24,"gender":false},
            {"name":"王五","age":25,"gender":true}];
        //获取李四的值
        alert(ps[1].name);
    </script>

3.遍历
示例

<script>
        var p = {"name":"战三",age:23,'gender':true};

        var ps = [{"name":"张三","age":23,"gender":true},
            {"name":"李四","age":24,"gender":false},
            {"name":"王五","age":25,"gender":true}];
        //获取p对象中所有的键和值
        //for in 循环
        for(var key in p){
            alert(key);
            alert(key+":"+p[key]);
        }
        //获取ps中的所有值
        for (var i = 0; i < ps.length; i++) {
            var per = ps[i];
            for (var key in per) {
                alert(key+":"+per[key]);
            }
        }
    </script>