android開發筆記之gson

現在手上負責的一個項目，有一個配置信息使用的是json來配置的，解析方式爲gson。就發一點時間寫了一個demo。

gson

gson 是google發佈的一個解析json的解析框架

gson github網站：
https://github.com/google/gson

jar包的下載地址：https://mvnrepository.com/artifact/com.google.code.gson/gson

Gson基本用法

toJson序列化.

public String toJson(Object src) {
public String toJson(Object src, Type typeOfSrc) {}
public void toJson(Object src, Appendable writer) throws JsonIOException {}
public void toJson(Object src, Type typeOfSrc, Appendable writer) throws JsonIOException {}
public void toJson(Object src, Type typeOfSrc, JsonWriter writer) throws JsonIOException {}
public String toJson(JsonElement jsonElement) {}
public void toJson(JsonElement jsonElement, Appendable writer) throws JsonIOException {}
public void toJson(JsonElement jsonElement, JsonWriter writer) throws JsonIOException {}

fromJson反序列化.

public <T> T fromJson(String json, Class<T> classOfT) throws JsonSyntaxException {}
public <T> T fromJson(String json, Type typeOfT) throws JsonSyntaxException {}
public <T> T fromJson(Reader json, Class<T> classOfT) throws JsonSyntaxException, JsonIOException {}
public <T> T fromJson(Reader json, Type typeOfT) throws JsonIOException, JsonSyntaxException {}
public <T> T fromJson(JsonReader reader, Type typeOfT) throws JsonIOException, JsonSyntaxException {}
public <T> T fromJson(JsonElement json, Class<T> classOfT) throws JsonSyntaxException {}
public <T> T fromJson(JsonElement json, Type typeOfT) throws JsonSyntaxException {}

Demo

我是使用AndroidStudio來做的此demo
(1)先在assets目錄中準備二個文件(test.json,test_list.json)，這裏要注意一下assets目錄的位置，如果不注意會導致讀取不到assets目錄下的json文件。

test.json

[
  {
    "name":"Tom",
    "age":13,
    "booleanKey":true,
    "school":"T-school",
    "address":{"province":"廣東","city":"惠州"}
  }
]

test_list.json

[
  {
    "name":"Tom",
    "age":13,
    "booleanKey":true,
    "school":"T-school",
    "address":{"province":"廣東","city":"惠州"}
  },
  {
    "name":"Ketty",
    "age":23,
    "booleanKey":false,
    "school":"K-school",
    "address":{"province":"廣東","city":"深圳"}
  },
  {
    "name":"John",
    "age":15,
    "booleanKey":true,
    "school":"J-school",
    "address":{"province":"廣東","city":"廣州"}
  }
]

(2)準備二個解析支持類
Address.java

package com.example.firstapp;

public class Address {

    private  String province;
    private String city;

    public void setCity(String city) {
        this.city = city;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    public String getCity() {
        return city;
    }

    public String getProvince() {
        return province;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("\"province\": ").append(province).append(", \"city\": ").append(city).append('\n');
        return sb.toString();
    }
}

Student.java

package com.example.firstapp;

public class Student {
    private String name;
    private int age;
    private String school;
    private boolean booleanKey;
    private Address address;


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

    public void setAddress(Address address) {
        this.address = address;
    }

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

    public void setSchool(String school) {
        this.school = school;
    }

    public Address getAddress() {
        return address;
    }

    public int getAge() {
        return age;
    }

    public String getName() {
        return name;
    }

    public String getSchool() {
        return school;
    }

    public void setBooleanKey(boolean booleanKey) {
        this.booleanKey = booleanKey;
    }

    public boolean getBooleanKey() {
        return booleanKey;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("\"name\": ").append(name).append(",\n")
                .append("\"age\": ").append(age).append(",\n")
                .append("\"booleanKey\": ").append(booleanKey).append(",\n")
                .append("\"school\": ").append(school).append(",\n")
                .append("\"address\": ").append(address).append('\n');

        return sb.toString();
    }


}

(3)導入gson包
app\build.gradle

dependencies {
	......
    implementation 'com.google.code.gson:gson:2.8.6'
}

(4)封閉一個幫忙類GsonHelper.java

package com.example.firstapp;

import android.content.Context;
import android.util.Log;
import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonParser;
import com.google.gson.reflect.TypeToken;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class GsonHelper {

    private static Gson mGson = new Gson();
    private final static String TAG = "GsonHelper";


    public static Object stringToObject(String json, Class classOfT){
        return  mGson.fromJson(json , classOfT ) ;
    }

    public static <T> String objectToString(T object) {
        return mGson.toJson(object);
    }
	
	//此接口有部分api已過期
    public static <T> List<T> stringToList(String json,Class<T> cls){
        List<T> list = new ArrayList<T>();
        JsonArray array = new JsonParser().parse(json).getAsJsonArray();
        for(final JsonElement elem : array){
            list.add(mGson.fromJson(elem, cls));
        }
        return list ;
    }

    public static <T> List<T> string2List(String json,Class<T> cls){
        TypeToken<List<T>> typeToken =
                new TypeToken<List<T>>() {
                };
        List<T> list = mGson.fromJson(json, typeToken.getType());
        return list ;
    }

    public static String getAssetsJson(Context context,String jsonFile){
        StringBuilder sb = new StringBuilder();
        InputStream inputStream = null;
        try {
            inputStream = context.getResources().getAssets().open(jsonFile);
            Log.i(TAG,"inputStream:"+inputStream);
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
            String line;
            while ((line = reader.readLine()) != null) {
                sb.append(line).append("\n");
            }
        } catch (IOException e) {
            Log.e(TAG,"e.printStackTrace():"+e.toString());
            e.printStackTrace();
        }finally {
            if(inputStream != null){
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return sb.toString();
    }
}

(5)實現gson解析json的核心方法

package com.example.firstapp;

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity ";

    private final String jsonFile1 = "test.json";
    private final String jsonFile2 = "test_list.json";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }

    private void init() {

        Address address = new Address();
        address.setCity("city_01");
        address.setProvince("province_01");
        Student student = new Student();
        student.setAddress(address);
        student.setAge(10);
        student.setName("name_01");
        student.setSchool("school_01");

        Log.i(TAG,"GsonHelper.objectToString(address):" + GsonHelper.objectToString(address));
        Log.i(TAG,"GsonHelper.objectToString(student):" + GsonHelper.objectToString(student));
        Log.i(TAG,"=========================01====================================");

        Address addressTrans = (Address) GsonHelper.stringToObject(GsonHelper.objectToString(address),Address.class);
        Log.i(TAG,"addressTrans:" + addressTrans);
        Student studentTrans = (Student) GsonHelper.stringToObject(GsonHelper.objectToString(student),Student.class);
        Log.i(TAG,"studentTrans:" + studentTrans);
        Log.i(TAG,"==========================02===================================");

        ArrayList<Student> arrayList;
        Log.i(TAG,"GsonHelper.getAssetsJson(this,jsonFile1):" + GsonHelper.getAssetsJson(this,jsonFile1));
        arrayList = (ArrayList)GsonHelper.string2List(GsonHelper.getAssetsJson(this,jsonFile1),Student.class);
        for (int i = 0;i < arrayList.size();i++){
            Log.i(TAG,"arrayList.get(i):" + arrayList.get(i));
        }

        Log.i(TAG,"===========================03==================================");
        Log.i(TAG,"GsonHelper.getAssetsJson(this,jsonFile2):" + GsonHelper.getAssetsJson(this,jsonFile2));
        arrayList = (ArrayList)GsonHelper.string2List(GsonHelper.getAssetsJson(this,jsonFile2),Student.class);
        for (int i = 0;i < arrayList.size();i++){
            Log.i(TAG,"arrayList.get(i):" + arrayList.get(i));
        }

        Log.i(TAG,"===========================04==================================");
        Log.i(TAG,"GsonHelper.getAssetsJson(this,jsonFile1):" + GsonHelper.getAssetsJson(this,jsonFile1));
        arrayList = (ArrayList)GsonHelper.stringToList(GsonHelper.getAssetsJson(this,jsonFile1),Student.class);
        for (int i = 0;i < arrayList.size();i++){
            Log.i(TAG,"arrayList.get(i):" + arrayList.get(i));
        }

        Log.i(TAG,"===========================05==================================");
        Log.i(TAG,"GsonHelper.getAssetsJson(this,jsonFile2):" + GsonHelper.getAssetsJson(this,jsonFile2));
        arrayList = (ArrayList)GsonHelper.stringToList(GsonHelper.getAssetsJson(this,jsonFile2),Student.class);
        for (int i = 0;i < arrayList.size();i++){
            Log.i(TAG,"arrayList.get(i):" + arrayList.get(i));
        }
    }
    
}

輸出測試結果：

 I/MainActivity: GsonHelper.objectToString(address):{"city":"city_01","province":"province_01"}
 I/MainActivity: GsonHelper.objectToString(student):{"address":{"city":"city_01","province":"province_01"},"age":10,"booleanKey":false,"name":"name_01","school":"school_01"}
 
 I/MainActivity: =========================01====================================
addressTrans:"province": province_01, "city": city_01
studentTrans:"name": name_01,
    "age": 10,
    "booleanKey": false,
    "school": school_01,
    "address": "province": province_01, "city": city_01

I/MainActivity: ==========================02===================================
GsonHelper.getAssetsJson(this,jsonFile1):[
      {
        "name":"Tom",
        "age":13,
        "booleanKey":true,
        "school":"T-school",
        "address":{"province":"廣東","city":"惠州"}
      }
    ]
    
I/MainActivity: arrayList.get(i):{name=Tom, age=13.0, booleanKey=true, school=T-school, address={province=廣東, city=惠州}}

I/MainActivity: ===========================03==================================
GsonHelper.getAssetsJson(this,jsonFile2):[
      {
        "name":"Tom",
        "age":13,
        "booleanKey":true,
        "school":"T-school",
        "address":{"province":"廣東","city":"惠州"}
      },
      {
        "name":"Ketty",
        "age":23,
        "booleanKey":false,
        "school":"K-school",
        "address":{"province":"廣東","city":"深圳"}
      },
      {
        "name":"John",
        "age":15,
        "booleanKey":true,
        "school":"J-school",
        "address":{"province":"廣東","city":"廣州"}
      }
    ]
    
I/MainActivity: arrayList.get(i):{name=Tom, age=13.0, booleanKey=true, school=T-school, address={province=廣東, city=惠州}}
I/MainActivity: arrayList.get(i):{name=Ketty, age=23.0, booleanKey=false, school=K-school, address={province=廣東, city=深圳}}
I/MainActivity: arrayList.get(i):{name=John, age=15.0, booleanKey=true, school=J-school, address={province=廣東, city=廣州}}

I/MainActivity: ===========================04==================================
GsonHelper.getAssetsJson(this,jsonFile1):[
      {
        "name":"Tom",
        "age":13,
        "booleanKey":true,
        "school":"T-school",
        "address":{"province":"廣東","city":"惠州"}
      }
    ]
arrayList.get(i):"name": Tom,
    "age": 13,
    "booleanKey": true,
    "school": T-school,
    "address": "province": 廣東, "city": 惠州
    
I/MainActivity: ===========================05==================================
GsonHelper.getAssetsJson(this,jsonFile2):[
      {
        "name":"Tom",
        "age":13,
        "booleanKey":true,
        "school":"T-school",
        "address":{"province":"廣東","city":"惠州"}
      },
      {
        "name":"Ketty",
        "age":23,
        "booleanKey":false,
        "school":"K-school",
        "address":{"province":"廣東","city":"深圳"}
      },
      {
        "name":"John",
        "age":15,
        "booleanKey":true,
        "school":"J-school",
        "address":{"province":"廣東","city":"廣州"}
      }
    ]
I/MainActivity: arrayList.get(i):"name": Tom,
    "age": 13,
    "booleanKey": true,
    "school": T-school,
    "address": "province": 廣東, "city": 惠州
I/MainActivity: arrayList.get(i):"name": Ketty,
    "age": 23,
    "booleanKey": false,
    "school": K-school,
    "address": "province": 廣東, "city": 深圳
I/MainActivity: arrayList.get(i):"name": John,
    "age": 15,
    "booleanKey": true,
    "school": J-school,
    "address": "province": 廣東, "city": 廣州

參考資料

Android Gson的使用總結
https://www.cnblogs.com/zhaoyanjun/p/5842601.html

淺談Android項目----JSON解析（4種解析技術詳解）
https://www.cnblogs.com/chengmuzhe/p/10596922.html

Android項目之JSON解析（3種解析技術詳解）
https://blog.csdn.net/mp624183768/article/details/79714085

android gson的使用
https://www.jianshu.com/p/6016be95d4f9