使用GSON库将Java中的map键值对应结构对象转换为JSON

前端技术 2023/08/31 Java

Map的存储结构式Key/Value形式,Key 和 Value可以是普通类型,也可以是自己写的JavaBean(本文),还可以是带有泛型的List.

（GSON的GitHub项目页：https://github.com/google/gson）

JavaBean

本例中您要重点看如何将Json转回为普通JavaBean对象时TypeToken的定义.

实体类:

public class Point { 
  private int x; 
  private int y; 
 
  public Point(int x, int y) { 
    this.x = x; 
    this.y = y; 
  } 
 
  public int getX() { 
    return x; 
  } 
 
  public void setX(int x) { 
    this.x = x; 
  } 
 
  public int getY() { 
    return y; 
  } 
 
  public void setY(int y) { 
    this.y = y; 
  } 
 
  @Override 
  public String toString() { 
    return \"Point [x=\" + x + \", y=\" + y + \"]\"; 
  } 
 
}

测试类:

import java.util.LinkedHashMap; 
import java.util.Map; 
 
import com.google.gson.Gson; 
import com.google.gson.GsonBuilder; 
import com.google.gson.reflect.TypeToken; 
 
public class GsonTest3 { 
 
  public static void main(String[] args) { 
    Gson gson = new GsonBuilder().enableComplexMapKeySerialization() 
        .create(); 
 
    Map<Point, String> map1 = new LinkedHashMap<Point, String>();// 使用LinkedHashMap将结果按先进先出顺序排列 
    map1.put(new Point(5, 6), \"a\"); 
    map1.put(new Point(8, 8), \"b\"); 
    String s = gson.toJson(map1); 
    System.out.println(s);// 结果:[[{\"x\":5,\"y\":6},\"a\"],[{\"x\":8,\"y\":8},\"b\"]] 
 
    Map<Point, String> retMap = gson.fromJson(s, 
        new TypeToken<Map<Point, String>>() { 
        }.getType()); 
    for (Point p : retMap.keySet()) { 
      System.out.println(\"key:\" + p + \" values:\" + retMap.get(p)); 
    } 
    System.out.println(retMap); 
 
    System.out.println(\"----------------------------------\"); 
    Map<String, Point> map2 = new LinkedHashMap<String, Point>(); 
    map2.put(\"a\", new Point(3, 4)); 
    map2.put(\"b\", new Point(5, 6)); 
    String s2 = gson.toJson(map2); 
    System.out.println(s2); 
 
    Map<String, Point> retMap2 = gson.fromJson(s2, 
        new TypeToken<Map<String, Point>>() { 
        }.getType()); 
    for (String key : retMap2.keySet()) { 
      System.out.println(\"key:\" + key + \" values:\" + retMap2.get(key)); 
    } 
 
  } 
}

结果:

[[{\"x\":5,\"y\":6},\"a\"],[{\"x\":8,\"y\":8},\"b\"]] 
key:Point [x=5, y=6] values:a 
key:Point [x=8, y=8] values:b 
{Point [x=5, y=6]=a, Point [x=8, y=8]=b} 
---------------------------------- 
{\"a\":{\"x\":3,\"y\":4},\"b\":{\"x\":5,\"y\":6}} 
key:a values:Point [x=3, y=4] 
key:b values:Point [x=5, y=6]

泛型List

实体类:

import java.util.Date; 
 
public class Student { 
  private int id; 
  private String name; 
  private Date birthDay; 
 
  public int getId() { 
    return id; 
  } 
 
  public void setId(int id) { 
    this.id = id; 
  } 
 
  public String getName() { 
    return name; 
  } 
 
  public void setName(String name) { 
    this.name = name; 
  } 
 
  public Date getBirthDay() { 
    return birthDay; 
  } 
 
  public void setBirthDay(Date birthDay) { 
    this.birthDay = birthDay; 
  } 
 
  @Override 
  public String toString() { 
    return \"Student [birthDay=\" + birthDay + \", id=\" + id + \", name=\" 
        + name + \"]\"; 
  } 
 
} 


public class Teacher { 
  private int id; 
 
  private String name; 
 
  private String title; 
 
  public int getId() { 
    return id; 
  } 
 
  public void setId(int id) { 
    this.id = id; 
  } 
 
  public String getName() { 
    return name; 
  } 
 
  public void setName(String name) { 
    this.name = name; 
  } 
 
  public String getTitle() { 
    return title; 
  } 
 
  public void setTitle(String title) { 
    this.title = title; 
  } 
 
  @Override 
  public String toString() { 
    return \"Teacher [id=\" + id + \", name=\" + name + \", title=\" + title 
        + \"]\"; 
  } 
 
}

测试类:

package com.tgb.lk.demo.gson.test4; 
 
import java.util.ArrayList; 
import java.util.Date; 
import java.util.LinkedHashMap; 
import java.util.List; 
import java.util.Map; 
 
import com.google.gson.Gson; 
import com.google.gson.reflect.TypeToken; 
 
public class GsonTest4 { 
  public static void main(String[] args) { 
    Student student1 = new Student(); 
    student1.setId(1); 
    student1.setName(\"李坤\"); 
    student1.setBirthDay(new Date()); 
 
    Student student2 = new Student(); 
    student2.setId(2); 
    student2.setName(\"曹贵生\"); 
    student2.setBirthDay(new Date()); 
 
    Student student3 = new Student(); 
    student3.setId(3); 
    student3.setName(\"柳波\"); 
    student3.setBirthDay(new Date()); 
 
    List<Student> stulist = new ArrayList<Student>(); 
    stulist.add(student1); 
    stulist.add(student2); 
    stulist.add(student3); 
 
    Teacher teacher1 = new Teacher(); 
    teacher1.setId(1); 
    teacher1.setName(\"米老师\"); 
    teacher1.setTitle(\"教授\"); 
 
    Teacher teacher2 = new Teacher(); 
    teacher2.setId(2); 
    teacher2.setName(\"丁老师\"); 
    teacher2.setTitle(\"讲师\"); 
    List<Teacher> teacherList = new ArrayList<Teacher>(); 
    teacherList.add(teacher1); 
    teacherList.add(teacher2); 
 
    Map<String, Object> map = new LinkedHashMap<String, Object>(); 
    map.put(\"students\", stulist); 
    map.put(\"teachers\", teacherList); 
 
    Gson gson = new Gson(); 
    String s = gson.toJson(map); 
    System.out.println(s); 
 
    System.out.println(\"----------------------------------\"); 
 
    Map<String, Object> retMap = gson.fromJson(s, 
        new TypeToken<Map<String, List<Object>>>() { 
        }.getType()); 
 
    for (String key : retMap.keySet()) { 
      System.out.println(\"key:\" + key + \" values:\" + retMap.get(key)); 
      if (key.equals(\"students\")) { 
        List<Student> stuList = (List<Student>) retMap.get(key); 
        System.out.println(stuList); 
      } else if (key.equals(\"teachers\")) { 
        List<Teacher> tchrList = (List<Teacher>) retMap.get(key); 
        System.out.println(tchrList); 
      } 
    } 
 
  } 
}

输出结果:

{\"students\":[{\"id\":1,\"name\":\"李坤\",\"birthDay\":\"Jun 22, 2012 9:48:19 PM\"},{\"id\":2,\"name\":\"曹贵生\",\"birthDay\":\"Jun 22, 2012 9:48:19 PM\"},{\"id\":3,\"name\":\"柳波\",\"birthDay\":\"Jun 22, 2012 9:48:19 PM\"}],\"teachers\":[{\"id\":1,\"name\":\"米老师\",\"title\":\"教授\"},{\"id\":2,\"name\":\"丁老师\",\"title\":\"讲师\"}]} 
---------------------------------- 
key:students values:[{id=1.0, name=李坤, birthDay=Jun 22, 2012 9:48:19 PM}, {id=2.0, name=曹贵生, birthDay=Jun 22, 2012 9:48:19 PM}, {id=3.0, name=柳波, birthDay=Jun 22, 2012 9:48:19 PM}] 
[{id=1.0, name=李坤, birthDay=Jun 22, 2012 9:48:19 PM}, {id=2.0, name=曹贵生, birthDay=Jun 22, 2012 9:48:19 PM}, {id=3.0, name=柳波, birthDay=Jun 22, 2012 9:48:19 PM}] 
key:teachers values:[{id=1.0, name=米老师, title=教授}, {id=2.0, name=丁老师, title=讲师}] 
[{id=1.0, name=米老师, title=教授}, {id=2.0, name=丁老师, title=讲师}]

本文地址：https://www.stayed.cn/item/983

转载请注明出处。

本站部分内容来源于网络,如侵犯到您的权益,请 联系我

我的博客

人生若只如初见，何事秋风悲画扇。

我的标签

随笔档案