fastjson值java对象与JSON串互转

com.alibaba.fastjson.JSONObject时经常会用到它的转换方法，包括Java对象转成JSON串、JSON对象，JSON串转成java对象、JSON对象，JSON对象转换Java对象、JSON串等，使用方法总结如下，持续更新…
1、Java对象–>JSON对象
(JSONObject)JSONObject.toJSON(Java对象实例)

 1 public class JSON2JavaTest{
 2     public static void main(String[] args) {
 3         Student stu = new Student("公众号BiggerBoy", "m", 2);
 4 
 5         //Java对象转化为JSON对象
 6         JSONObject jsonObject = (JSONObject) JSONObject.toJSON(stu);
 7         System.out.println("Java对象转化为JSON对象\n" + jsonObject);//{"name":"公众号编程大道","age":2,"sex":"m"}
 8         
 9     }
10 }
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2、Java对象–>JSON字符串
JSONObject.toJSONString(Java对象实例)

1 public class JSON2JavaTest{
2     public static void main(String[] args) {
3         Student stu = new Student("公众号BiggerBoy", "m", 2);
4 
5         //Java对象转换成JSON字符串 或者JSON.toJSONString(stu); JSONObject继承了JSON
6         String stuString = JSONObject.toJSONString(stu);
7         System.out.println("Java对象转换成JSON字符串\n" + stuString);//{"age":2,"name":"公众号编程大道","sex":"m"}
8     }
9 }
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3、JSON对象–>JSON字符串
JSONObject.toJSONString();

 1 public class JSON2JavaTest{
 2     public static void main(String[] args) {
 3         Student stu = new Student("公众号BiggerBoy", "m", 2);
 4 
 5         //先转成JSON对象
 6         JSONObject jsonObject = (JSONObject) JSONObject.toJSON(stu);
 7 
 8         //JSON对象转换为JSON字符串
 9         String jsonString = jsonObject.toJSONString();
10         System.out.println("JSON对象转换为JSON字符串\n" + jsonString);//{"name":"公众号编程大道","age":2,"sex":"m"}
11 
12     }
13 }
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4、JSON对象–>Java对象
JSONObject.toJavaObject(JSON对象实例, Java对象.class);

public class JSON2JavaTest{
   public static void main(String[] args) {
       Student stu = new Student("公众号BiggerBoy", "m", 2);

       //先转成JSON对象
       JSONObject jsonObject = (JSONObject) JSONObject.toJSON(stu);
       
       //JSON对象转换成Java对象
       Student student = JSONObject.toJavaObject(jsonObject, Student.class);
       System.out.println("JSON对象转换成Java对象\n" + student);//Student{name='公众号编程大道', sex='m', age=2}
   }
}
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5、JSON字符串–>JSON对象
JSONObject.parseObject(JSON字符串)

 1 public class JSON2JavaTest{
 2     public static void main(String[] args) {
 3         String stuString = "{\"age\":2,\"name\":\"公众号 BiggerBoy\",\"sex\":\"m\"}";
 4 
 5         //JSON字符串转换成JSON对象
 6         JSONObject jsonObject1 = JSONObject.parseObject(stuString);
 7         System.out.println("JSON字符串转换成JSON对象\n" + jsonObject1);//{"sex":"m","name":"公众号编程大道","age":2}
 8     }
 9 }
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6、JSON字符串–>Java对象
JSONObject.parseObject(JSON字符串, Java对象.class);

1 public class JSON2JavaTest{
2     public static void main(String[] args) {
3         String stuString = "{\"age\":2,\"name\":\"公众号 BiggerBoy\",\"sex\":\"m\"}";
4 
5         //JSON字符串转换成Java对象
6         Student student1 = JSONObject.parseObject(stuString, Student.class);
7         System.out.println("JSON字符串转换成Java对象\n" + student1);//Student{name='公众号编程大道', sex='m', age=2}
8     }
9 }
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如果student对象内有一个对象集合hobbies，相应的，JSON字符串转Map时如果不做处理，hobbies内的字段顺序可能会和原始hobbies字段值不一样

如下，第一次打印hobbies中的hobbyType跑到hobbyName前了，而原始JSON串中恰好和这相反，对于接口加解密生成签名时，字符串顺序尤为重要，若要保证原始顺序，可以加一个参数Feature.OrderedField

第二次打印的hobbies字段内的字符串顺序和原始字符串中一致。

String str1 = "{\"age\":2,\"hobbies\":[{\"hobbyName\":\"篮球\",\"hobbyType\":1},{\"hobbyName\":\"跳绳\",\"hobbyType\":2}],\"name\":\"公众号BiggerBoy\",\"sex\":\"m\"}";

Map map = JSONObject.parseObject(str1, Map.class);
System.out.println(JSONObject.toJSONString(map));
//{"hobbies":[{"hobbyType":1,"hobbyName":"篮球"},{"hobbyType":2,"hobbyName":"跳绳"}],"sex":"m","name":"公众号BiggerBoy","age":2}

Map map1 = JSONObject.parseObject(str1, Map.class, Feature.OrderedField);
System.out.println(JSONObject.toJSONString(map1));
//{"hobbies":[{"hobbyName":"篮球","hobbyType":1},{"hobbyName":"跳绳","hobbyType":2}],"sex":"m","name":"公众号BiggerBoy","age":2}
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7、JSON字符串–>List
List parseArray(JSON字符串, Java对象.class)

public class JSON2JavaTest{
   public static void main(String[] args) {
       String stuString = "[{\"age\":2,\"name\":\"公众号\",\"sex\":\"m\"},{\"age\":18,\"name\":\"BiggerBoy\",\"sex\":\"m\"}]";

       //JSON字符串转换成Java对象
       List<Student> studentList = JSONObject.parseArray(stuString, Student.class);
       System.out.println("JSON字符串转换成Java对象list\n" +studentList );
　　 }
}
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