$Java-json系列（二）：用JSONObject解析和处理json数据

本文中主要介绍JSONObject处理json数据时候的一些常用场景和方法。

（一）jar包下载

所需jar包打包下载百度网盘地址：https://pan.baidu.com/s/1c27Uyre

（二）常见场景及处理方法

1、解析简单的json字符串：

 　　　　 // 简单的json测试字符串
         public static final String JSON_SIMPLE = "{'name':'tom','age':16}";

         JSONObject obj = JSONObject.fromObject(JSON_SIMPLE);
         System.out.println("name is : " + obj.get("name"));
         System.out.println("age is : " + obj.get("age"));

输出：

name is : tom
age is : 16

2、解析嵌套的json字符串：

 　　　　 // 嵌套的json字符串
         public static final String JSON_MULTI = "{'name':'tom','score':{'Math':98,'English':90}}";
         JSONObject obj = JSONObject.fromObject(JSON_MULTI);
         System.out.println("name is : " + obj.get("name"));
         System.out.println("score is : " + obj.get("score"));

         JSONObject scoreObj = (JSONObject) obj.get("score");
         System.out.println("Math score is : " + scoreObj.get("Math"));
         System.out.println("English score is : " + scoreObj.get("English"));

输出：

name is : tom
score is : {"English":90,"Math":98}
Math score is : 98
English score is : 90

3、把bean对象转化成JSONObject对象：

Person、Info、Score类分别如下：（注：要定义成独立的三个public类，不能定义成内部类或非public类，否则会转换异常）

 public class Person {
     private String name;

     private Info info;

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public Info getInfo() {
         return info;
     }

     public void setInfo(Info info) {
         this.info = info;
     }

     @Override
     public String toString() {
         return "Person [name=" + name + ", info=" + info + "]";
     }

 }

 public class Info {
     private int age;
     private Score score;

     public int getAge() {
         return age;
     }

     public void setAge(int age) {
         this.age = age;
     }

     public Score getScore() {
         return score;
     }

     public void setScore(Score score) {
         this.score = score;
     }

     @Override
     public String toString() {
         return "Info [age=" + age + ", score=" + score + "]";
     }

 }

 public class Score {
     private String math;
     private String english;

     public String getMath() {
         return math;
     }

     public void setMath(String math) {
         this.math = math;
     }

     public String getEnglish() {
         return english;
     }

     public void setEnglish(String english) {
         this.english = english;
     }

     @Override
     public String toString() {
         return "Score [math=" + math + ", english=" + english + "]";
     }

 }

转换方法：

         Score score = new Score();
         score.setEnglish("A");
         score.setMath("B");

         Info info = new Info();
         info.setAge(20);
         info.setScore(score);

         Person person = new Person();
         person.setInfo(info);
         person.setName("Tim");

         JSONObject obj = JSONObject.fromObject(person);
         System.out.println(obj.toString());

输出：

{
    "name": "Tim",
    "info": {
        "score": {
            "english": "A",
            "math": "B"
        },
        "age": 20
    }
}

4、把json数组转换成JsonObject数组：

         // 数组形式的json
         public static final String JSON_ARRAY = "[{'name':'tom'},{'name':'john','age':20},{}]";

         JSONArray arr = JSONArray.fromObject(JSON_ARRAY);
         System.out.println(arr);

         for (int i = 0; i < arr.size(); i++) {
             JSONObject obj = arr.getJSONObject(i);
             System.out.println(obj.toString());
         }

输出：

[{"name":"tom"},{"name":"john","age":20},{}]
{"name":"tom"}
{"name":"john","age":20}
{}

5、构造一个json字符串：

         JSONObject obj = new JSONObject();
         obj.put("name", "tom");
         obj.put("age", 19);

         // 子对象
         JSONObject objContact = new JSONObject();
         objContact.put("tel", "123456");
         objContact.put("email", "tom@test.com");
         obj.put("contact", objContact);

         // 子数组对象
         JSONArray scoreArr = new JSONArray();
         JSONObject objEnglish = new JSONObject();
         objEnglish.put("course", "english");
         objEnglish.put("result", 100);
         objEnglish.put("level", "A");

         JSONObject objMath = new JSONObject();
         objMath.put("course", "math");
         objMath.put("result", 50);
         objMath.put("level", "D");

         scoreArr.add(objEnglish);
         scoreArr.add(objMath);

         obj.put("score", scoreArr);

         System.out.println(obj.toString());

输出：

{
    "score": [
        {
            "result": 100,
            "level": "A",
            "course": "english"
        },
        {
            "result": 50,
            "level": "D",
            "course": "math"
        }
    ],
    "contact": {
        "tel": "123456",
        "email": "tom@test.com"
    },
    "name": "tom",
    "age": 19
}

思考：输出的json中的字段的顺序有没有办法设置？