GSON實作Java物件的JSON序列化與反序列化的實例教程

class Examples {
 private int answer1 = 100;
 private String answer2 = "Hello world!";
 Examples(){
 }   // default constructor
}

Examples example1 = new Examples();
Gson gson = new Gson();
String json = gson.toJson(example1);

{"answer1":100,"answer2":"Hello world!"}

Examples example2= gson.fromJson(json,Examples.class);

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
   
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
   
class User{
  public User(String name,int age,StringBuffer sex,boolean isChild){
   this.name = name;
   this.age = age;
   this.sex = sex;
   this.isChild = isChild;
  }
  private String name;
  private int age;
  private StringBuffer sex;
  private boolean isChild;
  public String toString(){
   return "{name="+name+";age="+age+";sex="+sex+";isChild="+isChild+"}";
  }
  public int hashCode(){
   return name.hashCode()*100+age;
  }
}
   
public class GsonTest {
  public static void main(String[] args) {
   Gson gson = new Gson();
     
   System.out.println("1普通的Bean的转换**************************");
   System.out.println("将一个Bean转换成为json字符串->");
   User user1 = new User("凤姐",12,new StringBuffer("未知"),true);
   System.out.println("转换之前的user1"+user1);
   String json = gson.toJson(user1);
   System.out.println("User对象转换成为Json字符串，json==="+json);
     
   System.out.println("***************************");
   System.out.println("将一个json字符串转换成为Bean->");
   User user2 = gson.fromJson(json, User.class);
   System.out.println("转换成为的user2=="+user2);
   System.out.println();
     
   System.out.println("2Collection集合的转换**************************");
   System.out.println("将一个Bean的List集合转换成为json字符串->");
   Collection<User> userList1 = new ArrayList<User>();
   for(int i=0;i<3;i++){
    User user = new User("如花",10+i,new StringBuffer("男"),false);
    userList1.add(user);
   }
   json = gson.toJson(userList1);
   System.out.println("User的List集合对象转换成为Json字符串，json==="+json);
     
   System.out.println("***************************");
   System.out.println("将一个json字符串转换成为Bean的List集合->");
   Collection<User> userList2 =
      gson.fromJson(json,
         new TypeToken<Collection<User>>(){}.getType());
   System.out.println("转换成为的User的List集合，userList2="+userList2);
   System.out.println();
     
   System.out.println("3Array数组的转换**************************");
   System.out.println("将一个Bean的Array数组转换成为json字符串->");
   User [] userArray1 = new User[3];
   for(int i=0;i<userArray1.length;i++){
    userArray1[i] = new User("芙蓉",20,new StringBuffer("人妖"),true);
   }
   json = gson.toJson(userArray1);
   System.out.println("User的数组对象转换成为Json字符串,json==="+json);
     
   System.out.println("***************************");
   System.out.println("将一个json字符串转换成为Bean的数组对象->");
   User [] userArray2 = gson.fromJson(json, new TypeToken<User[]>(){}.getType());
   System.out.println("转换成为的User的数组对象,userArray2="+Arrays.toString(userArray2));
   System.out.println();
     
   System.out.println("4Map的转换**************************");
   System.out.println("将一个Bean的Map转换成为json字符串->");
   Map<String,User> map1 = new HashMap<String,User>();
   for(int i=0;i<3;i++){
    map1.put(""+(i+10), userArray1[i]);
   }
   json = gson.toJson(map1);
   System.out.println("User的Map集合转换成为Json字符串,json==="+json);
     
   System.out.println("***************************");
   System.out.println("将一个json字符串转换成为Bean的数组对象->");
   Map<String,User> map2 =
      gson.fromJson(json,
         new TypeToken<Map<String,User>>(){}.getType());
   System.out.println("转换成为的User的数组对象，map2=="+map2);
  }
}