引用gson

dependencies {
    implementation 'com.google.code.gson:gson:2.8.5'
}

方法一：Map对象转json

public void printJson1() {
    Map<String, Object> student = new HashMap<>();
    student.put("name", "野猿新一");
    student.put("age", 28);
    student.put("emails", new String[]{"yeyuanxinyi@sina.com", "yeyuanxinyi@sohu.com", "yeyuanxinyi@163.com"});

    Map<String, Object> girlfriend = new HashMap<>();
    girlfriend.put("name", "野援新二");
    girlfriend.put("age", 18);
    student.put("girlfriend", girlfriend);

    String json = new Gson().toJson(student);
    Log.d("json", json);
}

方法二：Java对象转json

// 首先定义一个Java类Student
public class Student {
    public String name;
    public int age;
    public String[] emails;
    public Student girlfriend;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

public void printJson2() {
    Student student = new Student("野猿新一", 28);
    student.emails = new String[]{"yeyuanxinyi@sina.com", "yeyuanxinyi@sohu.com", "yeyuanxinyi@163.com"};
    student.girlfriend = new Student("野援新二", 18);

    String json = new Gson().toJson(student);
    Log.d("json", json);
}

生成的json结果

以上代码生成的json结果是一样的，如下

{
  "age": 28,
  "emails": [
    "yeyuanxinyi@sina.com",
    "yeyuanxinyi@sohu.com",
    "yeyuanxinyi@163.com"
  ],
  "girlfriend": {
    "age": 18,
    "name": "野援新二"
  },
  "name": "野猿新一"
}

总结

• json内容少建议直接用Map生成，省去还要创建一个Java类的步骤。
• json内容多，层级复杂，建议用Java对象生成，代码结构比较清晰。