深入理解JSON数组、JSON对象、JSON字符串、普通数组的区别与操作整理

{ “firstName”:“John” , “lastName”:“Doe” }

{
“employees”: [
{ “firstName”:“John” , “lastName”:“Doe” },
{ “firstName”:“Anna” , “lastName”:“Smith” },
{ “firstName”:“Peter” , “lastName”:“Jones” }
]
}

var json={a:12,b:5,c:7};  //普通的json对象数据
var arr=[12,5,7];             //普通的数组
var jsonArray= [              //josn数组
 
        {"name":"zhang", "password":"123"},
 
        {"name":"yang", "password":"456"}
 
];
alert(json['a']);
alert(arr[0]);
alert(jsonArray[0].name);
//对普通json对象的遍历
for(var i in json){
    alert('第'+i+'个：'+json[i]);
}
//对数组的遍历
for(var i in arr){
    alert('第'+i+'个：'+arr[i]);
}
//对json数组的遍历
for(var p in jsonArray){//遍历json数组时，这么写p为索引，0,1
    alert(jsonArray[p].name + " " + jsonArray[p].password);
}
// 或者
for(var i = 0; i < jsonArray.length; i++){
        alert(jsonArray[i].name + " " + jsonArray[i].password);
}
//只有数组或者json数组才可以使用length方法。json对象使用length方法无效。

//如果json对象的子元素是数组或者json数组，也可以使用length方法。可以用于遍历数据

var jsonStr  = "{\"userId\":\"001\"}";  // json对象字符串
var jsonArryStr = "[{\"userId\":\"001\"},{\"userId\":\"002\"}]"; // json数组字符串
var jsonObj  = JSON.parse(jsonStr);     // 字符串转为json对象
//var jsonObj = $.parseJSON(jsonStr)    //Jquery中的方法
var jsonArry = JSON.parse(jsonArryStr); // 字符串转为json数组
var jsonStr  = JSON.stringify(jsonObj); // json对象转为字符串
var last     = jsonObj.toJSONString(); //将JSON对象转化为JSON字符串
var jsonArryStr=JSON.stringify(jsonArry);// json数组转为字符串
alert(jsonStr);
alert(jsonArryStr);
alert(jsonObj.userId);
alert(jsonArry[0]['userId']);
//JSON.stringify(obj)       将JSON对象转为字符串。
//JSON.parse(string)       将字符串转为JSON对象格式。

 //json对象转化成json数组对象
        var arr1=[];
        for(var i in jsonObj){
            //var o={};
            //o[i]=jsonObj[i];
            arr1.push(jsonObj[i]);            
        }

//第二种方法
<script>
//将对象转化为数组
    let obj={'未完成':5,'已完成':8,'待确认':4,'已取消':6};
     var arr = [];
    for (let i in obj) {
        //arr.push(obj[i]); //属性
        //arr.push(obj[i]); //值
        var o={};
        o[i]=obj[i];
        arr.push(o);
    }

    function objToArray(array) {
        var arr = []; 
        for (var i in array) {
            var o={};
            o[i]=array[i];
            arr.push(o); 
        }
        console.log(arr);
        //return arr;
    }
   // console.log(arr)
    objToArray(obj);
</script>

<dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.3</version>
</dependency>

  public static void main(String[] args) {

        //字符串转JSONObject
        String mapString = "{id:'211415034',name:'徐妍',age:'24'}";
        JSONObject json = JSON.parseObject(mapString);//json={"id":"211415034","name":"徐妍","age":"24"}

        //JSONObject转实体类
        Student json_student = JSONObject.toJavaObject(json, Student.class);
        String name = json.getString("name");
        System.out.println("name+json------" + name + "/n" + json);
        System.out.println("json_student---------" + json_student);
        //name+json------徐妍/n{"name":"徐妍","id":"211415034","age":"24"}
        //json_student---------Student{id=211415034, name='徐妍', age='24'}

        //json对象数组字符串(有里往外命名)
        String homeworklist = "[{id:'211415034',name:'蛋蛋',age:'24'},{id:'211415034',name:'闲闲',age:'24'}]";
        //对象数组字符串转JSONArray
        JSONArray json_list = JSON.parseArray(homeworklist);
        //对象数组字符串转List集合
        List<Student> stu1 = JSON.parseArray(homeworklist, Student.class);
        System.out.println("stu1----------" + stu1);
        //stu1----------[Student{id=211415034, name='蛋蛋', age='24'}, Student{id=211415034, name='闲闲', age='24'}]
        System.out.println("json_list-------" + json_list);
        //json_list-------[{"name":"蛋蛋","id":"211415034","age":"24"},{"name":"闲闲","id":"211415034","age":"24"}]
        //遍历JSONArray
        for (Object stu : json_list) {
            System.out.println("stu2--------" + stu);
        }
        //stu2--------{"name":"蛋蛋","id":"211415034","age":"24"}
        //stu2--------{"name":"闲闲","id":"211415034","age":"24"}

        //复杂的json字符串
        String homeworkMap = "[{id:'211415034',name:'蛋蛋',age:'24'}, {id:'211415034',name:'闲闲',age:['24']}]";
        //对象数组字符串转List集合
        List<Student> json_map = JSON.parseArray(homeworkMap, Student.class);
        System.out.println("json_map---------" + json_map);
        //json_map---------[Student{id=211415034, name='蛋蛋', age='24'}, Student{id=211415034, name='闲闲', age='["24"]'}]

        //将List转换成JSONArray，要先转换成json字符串
        JSONArray list1 = JSONArray.parseArray(JSON.toJSONString(json_map));
        System.out.println("list1---------" + list1);
        //list1---------[{"name":"蛋蛋","id":211415034,"age":"24"},{"name":"闲闲","id":211415034,"age":"[\"24\"]"}]

        //带名称的json数组对象字符串
        String homeworkMap2 = "{data:[{id:'211415034',name:'蛋蛋',age:['24','12']}, {id:'211415034',name:'闲闲',age:['24','12']}],stud:{id:'211415034',name:'这是stud',age:'24'}}";
        //先将json字符串转化成JSONObject
        JSONObject json_hp = JSON.parseObject(homeworkMap2);
        System.out.println("json_hp--------------" + json_hp);
        //json_hp--------------{"data":[{"name":"蛋蛋","id":"211415034","age":["24","12"]},{"name":"闲闲","id":"211415034","age":["24","12"]}],"stud":{"name":"这是stud","id":"211415034","age":"24"}}

        //获取key为data的数组
        System.out.println("data--------------" + json_hp.get("data"));
        //data--------------[{"name":"蛋蛋","id":"211415034","age":["24","12"]},{"name":"闲闲","id":"211415034","age":["24","12"]}]
        //获取key为data数组的stud对象
        System.out.println("stud--------------" + json_hp.get("stud"));
        //stud--------------{"name":"这是stud","id":"211415034","age":"24"}


        //强转 List<Map<String,Object>> list= (List<Map<String, Object>>) json_hp;
        List<Map<String, Object>> list = (List<Map<String, Object>>) json_hp.get("data");
        System.out.println("list------------" + list);
        //list------------[{"name":"蛋蛋","id":"211415034","age":["24","12"]},{"name":"闲闲","id":"211415034","age":["24","12"]}]

        //遍历list
        for (Map<String, Object> map : list) {
            System.out.println("map-----" + map);
            List age1 = (List) map.get("age");
            String age = String.valueOf(age1);
            for (Object age2 : age1) {
                System.out.println("age2-----------" + age2);
            }
            System.out.println("age-----------" + age);
        }
/*
        map-----{"name":"蛋蛋","id":"211415034","age":["24","12"]}
        age2-----------24
        age2-----------12
        age-----------["24","12"]
        map-----{"name":"闲闲","id":"211415034","age":["24","12"]}
        age2-----------24
        age2-----------12
        age-----------["24","12"]*/

    }