使用Gson将Java对象转换为Json

Gson是Google的一个开源项目，可以将Java对象转换成JSON，也可能将JSON转换成Java对象。

Gson里最重要的对象有2个Gson 和GsonBuilder。

Gson有2个最基本的方法
1) toJson() – 转换java 对象到JSON
2) fromJson() – 转换JSON到java对象

注意使用Gson时记得添加第三方类库gson-1.6.jar

    

main.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <Button android:id="@+id/btn01"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:text="开始解析01"/>
    <Button android:id="@+id/btn02"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:text="开始解析02"/>
    <Button android:id="@+id/btn03"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:text="开始解析03"/>
    <Button android:id="@+id/btn04"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:text="JavaToJson"/>
    <Button android:id="@+id/btn05"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:text="把对象的属性转换成json的名字"/>
</LinearLayout>

实体类User

package com.ljq.json;

import com.google.gson.annotations.SerializedName;

public class User {
    //将java对象的属性转换成指定的json名字
    @SerializedName("username")
    private String name;
    private int age;

    public User() {
        super();
    }

    public User(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

工具类JsonUtils

package com.ljq.json;

import java.io.StringReader;
import java.lang.reflect.Type;
import java.util.Iterator;
import java.util.LinkedList;


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

public class JsonUtils {
    public void parseJson01(String jsonData){
        try {
            //解析json对象首先要生产一个JsonReader对象
            JsonReader reader=new JsonReader(new StringReader(jsonData));
            reader.beginArray();
            while(reader.hasNext()){
                reader.beginObject();
                while(reader.hasNext()){
                    String tagName=reader.nextName();
                    if("name".equals(tagName)){
                        System.out.println("name--->"+reader.nextString());
                    }else if("age".equals(tagName)){
                        System.out.println("age--->"+reader.nextInt());
                    }
                }
                reader.endObject();
            }
            reader.endArray();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void parseJson02(String jsonData){
        Gson gson=new Gson();
        User user=gson.fromJson(jsonData, User.class);
        System.out.println("name--->" + user.getName());
        System.out.println("age---->" + user.getAge());
    }
    
    public void parseJson03(String jsonData){
        Type listType = new TypeToken<LinkedList<User>>(){}.getType();
        Gson gson=new Gson();
        LinkedList<User> users=gson.fromJson(jsonData, listType);
        for(User user:users){
            System.out.println("name--->" + user.getName());
            System.out.println("age---->" + user.getAge());
        }
        System.out.println("==================");
        for (Iterator iterator = users.iterator(); iterator.hasNext();) {
            User user = (User) iterator.next();
            System.out.println("name--->" + user.getName());
            System.out.println("age---->" + user.getAge());
        }
    }
}

JsonActivity

package com.ljq.json;

import com.google.gson.FieldNamingPolicy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class JsonActivity extends Activity {
    private Button btn01=null;
    private Button btn02=null;
    private Button btn03=null;
    private Button btn04=null;
    private Button btn05=null;
    private String jsonData01 = "[{\"name\":\"Michael\",\"age\":20},{\"name\":\"Mike\",\"age\":21}]";
    private String jsonData02 = "{\"name\":\"Michael\",\"age\":20}";    
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        btn01=(Button)findViewById(R.id.btn01);
        btn02=(Button)findViewById(R.id.btn02);
        btn03=(Button)findViewById(R.id.btn03);
        btn04=(Button)findViewById(R.id.btn04);
        btn05=(Button)findViewById(R.id.btn05);
        btn01.setOnClickListener(listener);
        btn02.setOnClickListener(listener);
        btn03.setOnClickListener(listener);
        btn04.setOnClickListener(listener);
        btn05.setOnClickListener(listener);
    }
    
    View.OnClickListener listener=new View.OnClickListener(){
        public void onClick(View v) {
            JsonUtils jsonUtils=new JsonUtils();
            switch (v.getId()) {
            case R.id.btn01:
                jsonUtils.parseJson01(jsonData01);
                break;
            case R.id.btn02:
                jsonUtils.parseJson02(jsonData02);
                break;
            case R.id.btn03:
                jsonUtils.parseJson03(jsonData01);
                break;
            case R.id.btn04:
                //把java对象转换成json
                User user01=new User("linjiqin", 24);
                Gson gson=new Gson();
                String obj=gson.toJson(user01);
                System.out.println(obj);//输出{"name":"linjiqin", "age":24}
                break;
            case R.id.btn05:
                //将java对象的属性转换成指定的json名字
                User user02=new User("lintepeng", 22);
                Gson gson2=new GsonBuilder().setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE).create();
                String obj2=gson2.toJson(user02);
                System.out.println(obj2);//输出{"username":"lintepeng","Age":22}
                break;
            }
        }
    };
}

运行结果