(Tutorial Android) Parsing JSON using GSON

GSON adalah library java yang digunakan untuk meng-convert objek java ke JSON atau sebaliknya. GSON memiliki fungsi serialization dan deserialization. Serialization berfungsi merubah JSON string menjadi objek java, sedangkan deserialization berfungsi merubah objek java menjadi bentuk JSON. Serialization dan deserialization di GSON menggunakan fungsi fromJson() dan toJson().

Pada tutorial sebelumnya http://wimsonevel.blogspot.co.id/2016/06/tutorial-android-json-parsing-example.html saya menjelaskan bagaimana memparsing JSON secara konvensional menggunakan fungsi JSONObject dan JSONArray. Nah, pada postingan kali ini tidak jauh beda yakni menggunakan library GSON untuk parsing. Bentuk JSON yang digunakan sama dengan sebelumnya yakni berikut :

{
     "firstName": "John",
     "lastName": "Smith",
     "age": 25,
     "address":
     {
         "streetAddress": "21 2nd Street",
         "city": "New York",
         "state": "NY",
         "postalCode": "10021"
     },
     "phoneNumber":
     [
         {
           "type": "home",
           "number": "212 555-1234"
         },
         {
           "type": "fax",
           "number": "646 555-4567"
         }
     ]
 }

Buat file dengan nama customer.json lalu letakkan di folder assets project android kita.

Pertama, tambahkan dependencies GSON di gradle.

compile 'com.google.code.gson:gson:2.6.2'

Tambahkan beberapa string resource di strings.xml

<resources>
    <string name="app_name">Android-GSON</string>

    <string name="first_name">First Name : %s</string>
    <string name="last_name">Last Name : %s</string>
    <string name="age">Age : %d</string>
    <string name="address">Address :</string>
    <string name="street">Street : %s</string>
    <string name="city">City : %s</string>
    <string name="state">State : %s</string>
    <string name="postal_code">Postal Code : %s</string>
    <string name="phone">Phone Number :</string>

</resources>

Buat layout activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="example.wim.androidgson.MainActivity">

    <TextView
        android:id="@+id/first_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/first_name" />

    <TextView
        android:id="@+id/last_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/last_name"
        android:layout_below="@+id/first_name" />

    <TextView
        android:id="@+id/age"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/age"
        android:layout_below="@+id/last_name" />

    <TextView
        android:id="@+id/address"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/address"
        android:layout_below="@+id/age" />

    <TextView
        android:id="@+id/street"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/street"
        android:layout_below="@+id/address"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"/>

    <TextView
        android:id="@+id/city"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/city"
        android:layout_below="@+id/street"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"/>

    <TextView
        android:id="@+id/state"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/state"
        android:layout_below="@+id/city"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"/>

    <TextView
        android:id="@+id/postal_code"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/postal_code"
        android:layout_below="@+id/state"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"/>

    <TextView
        android:id="@+id/phone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:text="@string/phone"
        android:layout_below="@+id/postal_code"/>

    <TextView
        android:id="@+id/home"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:layout_below="@+id/phone"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"/>

    <TextView
        android:id="@+id/fax"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dp"
        android:textSize="15sp"
        android:layout_below="@+id/home"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"/>

</RelativeLayout>

Kemudian buat fungsi untuk membaca file dari assets. Buat kelas FileUtil.java

import android.content.Context;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

/**
 * Created by Wim on 6/11/16.
 */
public class FileUtil {

    public static String copyFromAssets(Context context, String filename){
        StringBuilder buf = new StringBuilder();
        InputStream json = null;
        try {
            json = context.getAssets().open(filename);
            BufferedReader in = new BufferedReader(new InputStreamReader(json, "UTF-8"));
            String str;

            while ((str=in.readLine()) != null) {
                buf.append(str);
            }

            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return buf.toString();
    }

}

Nah, langkah selanjutnya yang paling penting adalah membuat kelas objek java dari bentuk JSON di atas.

Bentuk JSON :

{
     "firstName": "John",
     "lastName": "Smith",
     "age": 25,
     "address":
     {
         "streetAddress": "21 2nd Street",
         "city": "New York",
         "state": "NY",
         "postalCode": "10021"
     },
     "phoneNumber":
     [
         {
           "type": "home",
           "number": "212 555-1234"
         },
         {
           "type": "fax",
           "number": "646 555-4567"
         }
     ]
 }

Bentuk objek kelas java :

private String firstName;
private String lastName;
private int age;
private Address address;
private List<Phone> phoneNumber;

Objek di JSON dibuat menjadi bentuk variabel atau objek di java, sedangkan Array di JSON dibuat menjadi list.

Selengkapnya buat kelas dengan nama Customer.java

import java.util.List;

/**
 * Created by Wim on 6/11/16.
 */
public class Customer {

    private String firstName;
    private String lastName;
    private int age;
    private Address address;
    private List<Phone> phoneNumber;

    public Customer() {
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public int getAge() {
        return age;
    }

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

    public Address getAddress() {
        return address;
    }

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

    public List<Phone> getPhoneNumber() {
        return phoneNumber;
    }

    public void setPhoneNumber(List<Phone> phoneNumber) {
        this.phoneNumber = phoneNumber;
    }
}

Kemudian untuk objek address di JSON dibuat menjadi kelas Address.java

/**
 * Created by Wim on 6/11/16.
 */
public class Address {

    private String streetAddress;
    private String city;
    private String state;
    private String postalCode;

    public Address() {
    }

    public String getStreetAddress() {
        return streetAddress;
    }

    public void setStreetAddress(String streetAddress) {
        this.streetAddress = streetAddress;
    }

    public String getCity() {
        return city;
    }

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

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public String getPostalCode() {
        return postalCode;
    }

    public void setPostalCode(String postalCode) {
        this.postalCode = postalCode;
    }
}

Kemudian objek phoneNumber di JSON dibuat menjadi kelas Phone.java

/**
 * Created by Wim on 6/11/16.
 */
public class Phone {

    private String type;
    private String number;

    public Phone() {
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }
}

Langkah terakhir adalah melakukan parsing JSON ke kelas objek java. Untuk merubah bentuk JSON ke objek java menggunakan fungsi fromJson() berikut :

Gson gson = new Gson();
Customer customer = gson.fromJson(json, Customer.class);

Caranya sangat mudah.

Sekarang tinggal melengkapi source codenya di MainActivity.java sebagai berikut :

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import com.google.gson.Gson;

import java.util.List;

import example.wim.androidgson.model.Address;
import example.wim.androidgson.model.Customer;
import example.wim.androidgson.model.Phone;
import example.wim.androidgson.util.FileUtil;

public class MainActivity extends AppCompatActivity {

    TextView firstName;
    TextView lastName;
    TextView age;
    TextView street;
    TextView city;
    TextView state;
    TextView postalCode;
    TextView home;
    TextView fax;

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

        injectViews();
        parsingJson();
    }

    private void injectViews(){
        firstName = (TextView) findViewById(R.id.first_name);
        lastName = (TextView) findViewById(R.id.last_name);
        age = (TextView) findViewById(R.id.age);
        street = (TextView) findViewById(R.id.street);
        city = (TextView) findViewById(R.id.city);
        state = (TextView) findViewById(R.id.state);
        postalCode = (TextView) findViewById(R.id.postal_code);
        home = (TextView) findViewById(R.id.home);
        fax = (TextView) findViewById(R.id.fax);
    }

    private void parsingJson(){
        String json = FileUtil.copyFromAssets(this.getApplicationContext(), "customer.json");

        Gson gson = new Gson();
        Customer customer = gson.fromJson(json, Customer.class);

        firstName.setText(getResources().getString(R.string.first_name, customer.getFirstName()));
        lastName.setText(getResources().getString(R.string.last_name, customer.getLastName()));
        age.setText(getResources().getString(R.string.age, customer.getAge()));

        // Address
        Address address = customer.getAddress();

        street.setText(getResources().getString(R.string.street, address.getStreetAddress()));
        city.setText(getResources().getString(R.string.city, address.getCity()));
        state.setText(getResources().getString(R.string.state, address.getState()));
        postalCode.setText(getResources().getString(R.string.postal_code, address.getPostalCode()));

        // Phone
        List<Phone> phoneList = customer.getPhoneNumber();

        home.setText(phoneList.get(0).getType() +" : "+phoneList.get(0).getNumber());
        fax.setText(phoneList.get(1).getType() + " : "+phoneList.get(1).getNumber());
    }
}

Build dan jalankan maka hasilnya seperti berikut :

Source code lengkap dapat dilihat di https://github.com/wimsonevel/Android-GSON

Sekian dan semoga bermanfaat
Happy Coding :)

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