场景

通过情况下对前端输出json格式不需要关注字段顺序，但某些特殊场景需要设置字段输出顺序(例nginx需要对特殊字段顺序进行加密处理)；框架有默认的顺序，如 jackson 默认使用字段声明的顺序， fastjson 默认是使用字典序。

jackson

使用@JsonPropertyOrder指定顺序

public class JacksonController {public static void main(String[] args) throws JsonProcessingException {//1: 默认顺序:字段声明的顺序Cat1 cat1 = new Cat1();cat1.setAge(1);cat1.setName("咪咪");cat1.setHobby("sleep");ObjectMapper objectMapper = new ObjectMapper();String json = objectMapper.writeValueAsString(cat1);System.out.println("json:"+json.toString());//2: 使用@JsonPropertyOrder指定顺序Cat2 cat2 = new Cat2();cat2.setAge(1);cat2.setName("咪咪002");cat2.setHobby("eat");String json2 = objectMapper.writeValueAsString(cat2);System.out.println("json2:"+json2.toString());}
}@Data
class Cat1 {private String hobby;private String name;private Integer age;
}@Data
@JsonPropertyOrder({"name", "age", "hobby"})
class Cat2 {private String hobby;private String name;private Integer age;
}

fastjson

1、使用@JsonField的ordinal指定顺序，数越小优先级越高，默认为0
2、使用@JSONType的orders属性指定字段顺序

public class FastjsonController {public static void main(String[] args){//1: 默认顺序:字段声明的顺序Dog1 dog1 = new Dog1();dog1.setAge(1);dog1.setName("嘟嘟001");dog1.setHobby("eat");String json = JSON.toJSONString(dog1);System.out.println("默认顺序(字段声明的顺序):"+json.toString());//2: 使用@JsonField的ordinal指定顺序，数越小优先级越高，默认为0Dog2 dog2 = new Dog2();dog2.setAge(1);dog2.setName("嘟嘟002");dog2.setHobby("eat");String json2 = JSON.toJSONString(dog2);System.out.println("JsonField ordinal指定顺序:"+json2.toString());//3: 使用@JSONType的orders属性指定字段顺序Dog3 dog3 = new Dog3();dog3.setAge(1);dog3.setName("嘟嘟003");dog3.setHobby("eat");String json3 = JSON.toJSONString(dog3);System.out.println("JSONType orders指定顺序:"+json3.toString());}
}@Data
class Dog1 {private String hobby;private String name;private Integer age;
}@Data
class Dog2 {@JSONField(ordinal = 3)private String hobby;@JSONField(ordinal = 2)private String name;@JSONField(ordinal = 1)private Integer age;
}@Data
@JSONType(orders = {"name", "age", "hobby"})
class Dog3 {private String hobby;private String name;private Integer age;
}

注意

将json字段串转换成JSON对象时，如要保持原字段顺序，fastjson使用Feature.OrderedField参数；

JSON.parseObject(json, Feature.OrderedField);
SONObject.parseObject(json, Feature.OrderedField);