JSON解析类库之Gson（2） --- 泛型对象Map、List与JSON字符串互转
---Gson类库学习, 生成与解析json数据，json字符串与Java对象互转
一、前言
本文延续前一篇文章，继续介绍基本的Gson用法。这篇文章我们将介绍，如何实现Java泛型对象，如Map<>,List<>等泛型集合与JSON字符串互转。
二、Gson的基本使用
◆
◆
◆
泛型集合类型对象的序列化与反序列化
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◇
情况1 【非泛型】：Java数组的序列化与反序列化
数组与泛型不同，数组不是泛型。
Java Array ===》JSON String
JSON String ===》 Java Array
Gson
gson = new GsonBuilder()//
.setPrettyPrinting()//格式化输出（序列化）
.setDateFormat("yyyy-MM-dd HH:mm:ss") //序列化日期格式化输出
.create();
User user1 = new User("1", "王重阳", new Date());
User user2 = new User("2", "郭靖", new Date());
User user3 = new User("3", "黄蓉", new Date());
User[] usersArray = { user1, user2, user3 }; //数组对象
/**
* 序列化数组
*/
String jsonArrString = gson.toJson(usersArray);
System.out.println("数组序列化 ==》 " + jsonArrString);
/**
* 数组序列化 ==》 [
{
"id": "1",
"name": "王重阳",
"birthday": "2017-05-03 16:06:50"
},
{
"id": "2",
"name": "郭靖",
"birthday": "2017-05-03 16:06:50"
},
{
"id": "3",
"name": "黄蓉",
"birthday": "2017-05-03 16:06:50"
}
]
*/
/**
* JSON字符串反序列化成数组对象，数组反序列化的类型参是可以直接用数组的class, 如
User
[].class
*/
User[] usersArr = gson.fromJson(jsonArrString, User[].class);
for (int i = 0; i < usersArr.length; i++) {
User u1 = usersArr[i];
System.out.println("JSON字符串反序列化成数组对象 ==》 " + u1);
/*
* User对象 ==》 User [id=1, name=王重阳, birthday=Wed May 03 16:14:14 CST 2017]
User对象 ==》 User [id=2, name=郭靖, birthday=Wed May 03 16:14:14 CST 2017]
User对象 ==》 User [id=3, name=黄蓉, birthday=Wed May 03 16:14:14 CST 2017]
*/
}
注意：数组的字节码文件可以反射出具体的数组中的对象类型，但是List<User>不能直接用List<User>.class 或List.class。因为泛型编译成字节码时是擦除类型的，List<User>和List<Dept>在编译成字节码后完全一样，没区别。
泛型集合得用
new TypeToken(List<User>){}.getType()
作为反序列的第二个参数。
◇
情况2 ：Java Map的序列化与反序列化
实体类：
public
class
Role {
private String id;
private String name;
private String title;
public Role() {
super();
}
public Role(String id, String name, String title) {
super();
this.id = id;
this.name = name;
this.title = title;
}
//为了代码简洁，这里移除了getter和setter方法、toString方法等
}
Map<String, List<? extends Object>>
===》JSON String
JSON String
===》
Map
<String,
List
<Object>>
package
com.chunlynn.gson;
import java.lang.reflect.Type;
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.GsonBuilder;
import com.google.gson.reflect.TypeToken;
public class GsonTest10 {
public static void main(String[] args) {
Gson gson = new GsonBuilder()//
.setPrettyPrinting()//格式化输出（序列化）
.setDateFormat("yyyy-MM-dd HH:mm:ss") //序列化日期格式化输出
.create();
User user1 = new User("1", "王重阳", new Date());
User user2 = new User("2", "郭靖", new Date());
User user3 = new User("3", "黄蓉", new Date());
List<User> userList = new ArrayList<User>();
userList.add(user1);
userList.add(user2);
userList.add(user3);
Role role1 = new Role("1001", "chunlynn", "admin");
Role role2 = new Role("1002", "jeff", "vistor");
List<Role> roleList = new ArrayList<Role>();
roleList.add(role1);
roleList.add(role2);
Map<String, List<? extends Object>> map = new LinkedHashMap<String, List<? extends Object>>(); //可以
// Map<String, Object> map2 = new LinkedHashMap<String, Object>(); //可以
// Map<String, List<Object>> map3 = new LinkedHashMap<String, List<Object>>();//这种不行,类型不匹配，put时无法添加
map.put("users", userList);
map.put("roles", roleList);
/**
* [7] Map泛型序列化成JSON字符串
*/
String jsonStr = gson.toJson(map);
System.out.println("Map泛型序列化成JSON字符串 ==》 " + jsonStr);
/*Map泛型序列化成JSON字符串 ==》
{
"users": [
{
"id": "1",
"name": "王重阳",
"birthday": "2017-05-03 17:04:12"
},
{
"id": "2",
"name": "郭靖",
"birthday": "2017-05-03 17:04:12"
},
{
"id": "3",
"name": "黄蓉",
"birthday": "2017-05-03 17:04:12"
}
],
"roles": [
{
"id": "1001",
"name": "chunlynn",
"title": "admin"
},
{
"id": "1002",
"name": "jeff",
"title": "vistor"
}
]
}
*/
/**
* [8] JSON字符串反序列化成包含Map泛型类型
*/
// 反序列化成那种泛型类型的设置，Map的泛型类型
Type mtype = new TypeToken<Map<String, List<Object>>>() {
}.getType();
Map<String, List<Object>> retMap = gson.fromJson(jsonStr, mtype);
System.out.println("retMap == > " + retMap);
for (Map.Entry<String, List<Object>> p : retMap.entrySet()) {
System.out.println("key ==" + p.getKey() + " , " + "value==" + p.getValue());
/*
* key ==users , value==[{id=1, name=王重阳, birthday=2017-05-03 17:55:16}, {id=2, name=郭靖, birthday=2017-05-03 17:55:16}, {id=3, name=黄蓉, birthday=2017-05-03 17:55:16}]
key ==roles , value==[{id=1001, name=chunlynn, title=admin}, {id=1002, name=jeff, title=vistor}]
*/
}
Map<String, Object> retMap2 = gson.fromJson(jsonStr, mtype);
System.out.println("retMap2 == > " + retMap2);
for (Map.Entry<String, Object> p : retMap2.entrySet()) {
System.out.println("key2 ==" + p.getKey() + " , " + "value2==" + p.getValue());
/*
* key2 ==users , value2==[{id=1, name=王重阳, birthday=2017-05-03 17:55:16}, {id=2, name=郭靖, birthday=2017-05-03 17:55:16}, {id=3, name=黄蓉, birthday=2017-05-03 17:55:16}]
key2 ==roles , value2==[{id=1001, name=chunlynn, title=admin}, {id=1002, name=jeff, title=vistor}]
*/
}
Map<String, List<? extends Object>> retMap3 = gson.fromJson(jsonStr, mtype);
System.out.println("retMap3 == > " + retMap3);
for (Map.Entry<String, List<? extends Object>> p : retMap3.entrySet()) {
System.out.println("key3 ==" + p.getKey() + " , " + "value3==" + p.getValue());
/*
* key3 ==users , value3==[{id=1, name=王重阳, birthday=2017-05-03 17:55:16}, {id=2, name=郭靖, birthday=2017-05-03 17:55:16}, {id=3, name=黄蓉, birthday=2017-05-03 17:55:16}]
key3 ==roles , value3==[{id=1001, name=chunlynn, title=admin}, {id=1002, name=jeff, title=vistor}]
*/
}
/*
retMap == > {users=[{id=1, name=王重阳, birthday=2017-05-03 17:43:05}, {id=2, name=郭靖, birthday=2017-05-03 17:43:05}, {id=3, name=黄蓉, birthday=2017-05-03 17:43:05}],
roles=[{id=1001, name=chunlynn, title=admin}, {id=1002, name=jeff, title=vistor}]}
retMap2 == > {users=[{id=1, name=王重阳, birthday=2017-05-03 17:43:05}, {id=2, name=郭靖, birthday=2017-05-03 17:43:05}, {id=3, name=黄蓉, birthday=2017-05-03 17:43:05}],
roles=[{id=1001, name=chunlynn, title=admin}, {id=1002, name=jeff, title=vistor}]}
retMap3 == > {users=[{id=1, name=王重阳, birthday=2017-05-03 17:43:05}, {id=2, name=郭靖, birthday=2017-05-03 17:43:05}, {id=3, name=黄蓉, birthday=2017-05-03 17:43:05}],
roles=[{id=1001, name=chunlynn, title=admin}, {id=1002, name=jeff, title=vistor}]}
*/
}
}
注：
TypeToken
的构造方法是
protected
修饰的，所以上面才会写成new TypeToken<List<String>>(){}.getType()
而不是
new TypeToken<List<String>>().getType()
。
◇
情况3 ：Java Map高级的序列化与反序列化
★ Map的key为复杂对象形式
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（本节），还可以是带有泛型的List（上节）。
实体类:
public
class
Point {
private int x;
private int y;
public Point(int x, int y) {
super();
this.x = x;
this.y = y;
}
//为了代码简洁，这里移除了getter和setter方法、toString方法等
}
测试类：
package
com.chunlynn.gson;
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 GsonTest11 {
public static void main(String[] args) {
Gson gson = new GsonBuilder()//
//.setPrettyPrinting()//格式化输出（序列化）
.enableComplexMapKeySerialization() ////支持Map的key为复杂对象的形式
.create();
/**
* [9]普通Map<String,Object>形式的泛型序列化与反序列化，Map的key为简单String形式
*/
Map<String, Point> map1 = new LinkedHashMap<String, Point>();
map1.put("a", new Point(3, 4));
map1.put("b", new Point(5, 6));
String jsonStr1 = gson.toJson(map1);
System.out.println("普通Map对象的序列化 ===》 " + jsonStr1);
// 普通Map对象的序列化 ===》 {"a":{"x":3,"y":4},"b":{"x":5,"y":6}}
Map<String, Point> retMap1 = gson.fromJson(jsonStr1, new TypeToken<Map<String, Point>>() {
}.getType());
for (String key : retMap1.keySet()) {
System.out.println("key=" + key + ", values=" + retMap1.get(key));
}
//key=a, values=Point [x=3, y=4]
//key=b, values=Point [x=5, y=6]
/**
* [10]特殊Map<Object,String>形式的泛型序列化与反序列化，Map的key为复杂对象形式
*/
Map<Point, String> map2 = new LinkedHashMap<Point, String>();
map2.put(new Point(7, 8), "c");
map2.put(new Point(9, 10), "d");
String jsonStr2 = gson.toJson(map2);
System.out.println("Map的key为复杂对象形式的Map对象的序列化 ===》 " + jsonStr2);
//Map的key为复杂对象形式的Map对象的序列化 ===》 [[{"x":7,"y":8},"c"],[{"x":9,"y":10},"d"]]
Map<Point, String> retMap2 = gson.fromJson(jsonStr2, new TypeToken<Map<Point, String>>() {
}.getType());
for (Point pKey : retMap2.keySet()) {
System.out.println("key=" + pKey + ", values:" + retMap2.get(pKey));
}
// key=Point [x=7, y=8], values:c
// key=Point [x=9, y=10], values:d
}
}
Map、List泛型的完结。
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版权声明：本文为博主（chunlynn）原创文章，转载请注明出处 ：http://blog.youkuaiyun.com/chenchunlin526/article/details/71173404
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