Gson使用一(Gson)

一.概述

从结构上看Json,所有的数据(data)最终都可以分解成三种类型:

  1. 第一种类型是标量(scalar),也就是一个单独的字符串(string)或数字(numbers),比如"ickes"这个字符串。
  2. 第二种类型是序列(sequence),又叫做数组(array)或列表(List),比如["北京","上海"]。
  3. 第三种类型是映射(mapping),又叫做散列(hash)或字典(dictionary),比如"name":"ickes"。

Json的规格非常简单,而且Douglas Crockford声称这个规格永远不必升级,因为该规定的都规定了。

  1. 并列的数据之间用逗号(",")分隔。
  2. 映射用冒号(":")表示。
  3. 集合(数组)用方括号("[]")表示。
  4. 对象用大括号("{}")表示

二、简单转换

实体类User:

package com.ickes.json.daomain;

import java.util.Date;

public class User {
	private String  id;
	private String  userName;
	private String  userPwd;
	private Integer age;
	private Float   price;
	private Date    birthday;
	
	public User(String id, String userName, String userPwd, Integer age,
			Float price, Date birthday) {
		this.id = id;
		this.userName = userName;
		this.userPwd = userPwd;
		this.age = age;
		this.price = price;
		this.birthday = birthday;
	}
        get和set方法省略........!
	@Override
	public String toString() {
		return "User [id=" + id + ", userName=" + userName + ", userPwd="
				+ userPwd + ", age=" + age + ", price=" + price + ", birthday="
				+ birthday + "]";
	}
	
}

单个对象之间的转换,参考实例

import java.util.Date;

import com.google.gson.Gson;
import com.ickes.json.daomain.User;

/**
 * 简单对象之间的转换
 * @author Ickes
 */
public class GsonTest {
	public static void main(String[] args) {
		Gson gson = new Gson();
		User user = new User("A001", "xl","xl_123",24,12000F,new Date());
		//java对象转换为Json字符串
		String json=gson.toJson(user);
		System.out.println("java对象转json字符串:"+json);
		//Json字符串转换为java对象
		User user1 = gson.fromJson(json,User.class);
		System.out.println("json字符串转java对象:"+user1.toString());
	}
}

返回结果

java对象转json字符串:
{"id":"A001","userName":"xl","userPwd":"xl_123","age":24,"price":12000.0,"birthday":"Jan 13, 2015 1:43:22 PM"}
json字符串转java对象:
User [id=A001, userName=xl, userPwd=xl_123, age=24, price=12000.0, birthday=Tue Jan 13 13:43:22 CST 2015]

  

 集合之间的转换

package com.ickes.json;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import com.google.gson.reflect.TypeToken;
import com.google.gson.Gson;
import com.ickes.json.daomain.User;
/**
 * 集合之间的转换
 * @author Ickes
 *
 */
public class GsonTest {
	public static void main(String[] args) {
		Gson gson = new Gson();
		User user1 = new User("A001", "xl","xl_123",24,12000F,new Date());
		User user2 = new User("A002", "x2","xl_123",24,13000F,new Date());
		User user3 = new User("A003", "x3","xl_123",24,14000F,new Date());
		//集合对象转json
		List<User> users = new ArrayList<User>();
		users.add(user1);
		users.add(user2);
		users.add(user3);
		String jsonObj =gson.toJson(users);
		System.out.println("List集合对象转换为Json字符串:"+jsonObj);
		//集合字符串转json
		List<String> strs = new ArrayList<String>();
		strs.add("aaaa");
		strs.add("bbbb");
		strs.add("cccc");
		String jsonStr = gson.toJson(strs);
		System.out.println("List集合字符串转换为Json字符串:"+jsonStr);
		
		//json转集合对象
		Type typeObj = new TypeToken<List<User>>(){}.getType();
		users=gson.fromJson(jsonObj,typeObj);
		System.out.println("Json字符串转换为List集合对象:");
		for (User user : users) {
			System.out.println(user);
		}
		//json转集合字符串
		Type typeStr = new TypeToken<List<String>>(){}.getType();
		strs=gson.fromJson(jsonStr,typeStr);
		System.out.println("Json字符串转换为List集合字符串:"+strs);
		
	}
}

 输出结果

List集合对象转换为Json字符串:
[{"id":"A001","userName":"xl","userPwd":"xl_123","age":24,"price":12000.0,"birthday":"Jan 13, 2015 1:41:35 PM"},
 {"id":"A002","userName":"x2","userPwd":"xl_123","age":24,"price":13000.0,"birthday":"Jan 13, 2015 1:41:35 PM"},
 {"id":"A003","userName":"x3","userPwd":"xl_123","age":24,"price":14000.0,"birthday":"Jan 13, 2015 1:41:35 PM"}]
List集合字符串转换为Json字符串:["aaaa","bbbb","cccc"]
Json字符串转换为List集合对象:
User [id=A001, userName=xl, userPwd=xl_123, age=24, price=12000.0, birthday=Tue Jan 13 13:41:35 CST 2015]
User [id=A002, userName=x2, userPwd=xl_123, age=24, price=13000.0, birthday=Tue Jan 13 13:41:35 CST 2015]
User [id=A003, userName=x3, userPwd=xl_123, age=24, price=14000.0, birthday=Tue Jan 13 13:41:35 CST 2015]
Json字符串转换为List集合字符串:[aaaa, bbbb, cccc]