使用GSON库将Java中的map键值对应结构对象转换为JSON

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}]