Gson入门教程【原】

 gson一个jar包就能纵横天下,不像Json-lib.jar依赖其它jar包.

点击右边图片下载jar包       或以下链接

 http://central.maven.org/maven2/com/google/code/gson/gson/2.1/gson-2.1.jar

定义一个JavaBean类Person:

package ccc.json;

public class Person {
    Integer id;
    String name;
    String place;

    public Person(Integer id, String name, String place) {
        super();
        this.id = id;
        this.name = name;
        this.place = place;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPlace() {
        return place;
    }

    public void setPlace(String place) {
        this.place = place;
    }

    @Override
    public String toString() {
        return "Person [id=" + id + ", name=" + name + ", place=" + place + "]";
    }

    
}

再定义一个JsonService.

用于生成各种形式的对象如Object,List,List<Map<String,Object>> :

package ccc.json;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class JsonService {  
    
    public Person getPerson(){  
        Person person=new Person(123,"bobo","HangZhou");  
        return person;  
    }  
      
    public List<Person> getPersonList(){  
        List<Person> list=new ArrayList<Person>();  
        Person person1 = new Person(123,"sisi","BeiJing");  
        Person person2 = new Person(2002, "bobo", "HangZhou");
        list.add(person1);  
        list.add(person2);  
          
        return list;  
          
    }  
    public List<String> getList(){  
        List<String> list=new ArrayList<String>();  
        list.add("BeiJing");  
        list.add("HangZhou");  
        return list;  
    }  
      
    public Map<String,Object> getMap(){  
        Map<String,Object> map=new HashMap<String, Object>();  
        map.put("id", 123);  
        map.put("name","sisi");  
        map.put("place", "BeiJing"); 
        return map; 
    }
    
    public List<Map<String,Object>> getlistMap(){  
        List<Map<String,Object>> list=new ArrayList<Map<String,Object>>();  
        Map<String,Object> map1=new HashMap<String, Object>();  
        map1.put("id", 123);  
        map1.put("name","sisi");  
        map1.put("place", "BeiJing");  
        Map<String,Object> map2=new HashMap<String, Object>();  
        map2.put("id", 456);  
        map2.put("name","bobo");  
        map2.put("place", "HangZhou");  
        list.add(map1);  
        list.add(map2);  
        return list;  
    }  
  
} 

GsonDemo入口:

package ccc.json;

import java.util.List;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class Json_demo {
    public static void main(String[] args) {
        Gson gson = new Gson();
        JsonService service = new JsonService();
        
        String str1 = gson.toJson(service.getPerson());
        System.out.println("1: "+str1);
//        1: {"id":123,"name":"bobo","place":"HangZhou"}
        
        String str4 = gson.toJson(service.getMap());
        System.out.println("2: "+str4);
//        2: {"id":123,"name":"sisi","place":"BeiJing"}
        
        String str2 = gson.toJson(service.getPersonList());
        System.out.println("3: "+str2);
//        3: [{"id":123,"name":"sisi","place":"BeiJing"},{"id":2002,"name":"bobo","place":"HangZhou"}]
        
        String str3 = gson.toJson(service.getList());
        System.out.println("4: "+str3);
//        4: ["BeiJing","HangZhou"]
        
        String str5 = gson.toJson(service.getlistMap());
        System.out.println("5: "+str5);
//        5: [{"id":123,"name":"sisi","place":"BeiJing"},{"id":456,"name":"bobo","place":"HangZhou"}]
        
        
        Person  personA = gson.fromJson(str4, Person.class);
        System.out.println(personA);
//        Person [id=123, name=sisi, place=BeiJing]
        
        Map<String,Object> mapA = gson.fromJson(str4, Map.class);
        System.out.println(mapA);
//        {id=123.0, name=sisi, place=BeiJing}
        
        //在已经知道要转成List的情况下可以直接带List.class参数
        List<Map> list = gson.fromJson(str5 /*str2*/, List.class);
        for(Map map : list){
            String s = gson.toJson(map);
            Person p =gson.fromJson(s, Person.class);
            System.out.println(p);
        }
//        Person [id=123, name=sisi, place=BeiJing]
//        Person [id=456, name=bobo, place=HangZhou]
        
        //转泛型的时候会把int转成double
        List<Map<String,Object>> list_map = gson.fromJson(str5, new TypeToken<List<Map<String,Object>>>(){}.getType());
        for(Map m: list_map){
            System.out.println(m);
        }
//        {id=123.0, name=sisi, place=BeiJing}
//        {id=456.0, name=bobo, place=HangZhou}
        
        //转Person可以把double的小数舍去
        List<Person> personList = gson.fromJson(str2 /*str5*/, new TypeToken<List<Person>>(){}.getType());
        for(Person p: personList){
            System.out.println(p);
        }
//        Person [id=123, name=sisi, place=BeiJing]
//        Person [id=2002, name=bobo, place=HangZhou]
    }
}

gson格式化-美化

Gson gson = new GsonBuilder().setPrettyPrinting().create();
String gsonInfo = gson.toJson(map);

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