使用GSON库将Java中的map键值对应结构对象转换为JSON
作者：李坤
GSON是由Google开发并开源的实现Java对象与JSON之间相互转换功能的类库,这里我们来看一下使用GSON库将Java中的map键值对应结构对象转换为JSON的示例:
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}]