آموزش استفاده از Retrofit 2 به عنوان REST client

@GET("users")
Call<List<User>> getUsers();

@GET("users/{name}/commits")
Call<List<Commit>> getCommitsByName(@Path("name") String name); 

@GET("users")
Call<User> getUserById(@Query("id") Integer id);

@POST("users")
Call<User postUser(@Body User user)

// retrofit
implementation 'com.squareup.retrofit2:retrofit:2.1.0'
implementation 'com.squareup.retrofit2:converter-gson:2.1.0'
 
// Junit
testImplementation("org.junit.jupiter:junit-jupiter-api:5.0.0")
testRuntime("org.junit.jupiter:junit-jupiter-engine:5.0.0")
// to run JUnit 3/4 tests:
testImplementation("junit:junit:4.12")
testRuntime("org.junit.vintage:junit-vintage-engine:4.12.0")

public class Applications {
@SerializedName("id")
@Expose
private String id;
@SerializedName("cat_id")
@Expose
private String catId;
@SerializedName("title")
@Expose
private String title;
@SerializedName("icon")
@Expose
private String icon;
@SerializedName("packageName")
@Expose
private String packageName;
@SerializedName("versionCode")
@Expose
private String versionCode;
@SerializedName("versionName")
@Expose
private String versionName;
@SerializedName("shortDescription")
@Expose
private String shortDescription;
@SerializedName("fullDescription")
@Expose
private String fullDescription;
@SerializedName("price")
@Expose
private String price;
@SerializedName("rate")
@Expose
private String rate;
@SerializedName("downloadLink")
@Expose
private String downloadLink;
@SerializedName("number_installs")
@Expose
private String numberInstalls;
@SerializedName("minSDK")
@Expose
private String minSDK;
@SerializedName("developer")
@Expose
private String developer;
@SerializedName("bulk")
@Expose
private String bulk;
 
public String getId() {
return id;
}
 
public void setId(String id) {
this.id = id;
}
 
public String getCatId() {
return catId;
}
 
public void setCatId(String catId) {
this.catId = catId;
}
 
public String getTitle() {
return title;
}
 
public void setTitle(String title) {
this.title = title;
}
 
public String getIcon() {
return icon;
}
 
public void setIcon(String icon) {
this.icon = icon;
}
 
public String getPackageName() {
return packageName;
}
 
public void setPackageName(String packageName) {
this.packageName = packageName;
}
 
public String getVersionCode() {
return versionCode;
}
 
public void setVersionCode(String versionCode) {
this.versionCode = versionCode;
}
 
public String getVersionName() {
return versionName;
}
 
public void setVersionName(String versionName) {
this.versionName = versionName;
}
 
public String getShortDescription() {
return shortDescription;
}
 
public void setShortDescription(String shortDescription) {
this.shortDescription = shortDescription;
}
 
public String getFullDescription() {
return fullDescription;
}
 
public void setFullDescription(String fullDescription) {
this.fullDescription = fullDescription;
}
 
public String getPrice() {
return price;
}
 
public void setPrice(String price) {
this.price = price;
}
 
public String getRate() {
return rate;
}
 
public void setRate(String rate) {
this.rate = rate;
}
 
public String getDownloadLink() {
return downloadLink;
}
 
public void setDownloadLink(String downloadLink) {
this.downloadLink = downloadLink;
}
 
public String getNumberInstalls() {
return numberInstalls;
}
 
public void setNumberInstalls(String numberInstalls) {
this.numberInstalls = numberInstalls;
}
 
public String getMinSDK() {
return minSDK;
}
 
public void setMinSDK(String minSDK) {
this.minSDK = minSDK;
}
 
public String getDeveloper() {
return developer;
}
 
public void setDeveloper(String developer) {
this.developer = developer;
}
 
public String getBulk() {
return bulk;
}
 
public void setBulk(String bulk) {
this.bulk = bulk;
}
}

public class APIClient {
 
    private static Retrofit retrofit;
    private final static String BaseURL = http://androidsupport.ir/market/";
 
    public static Retrofit getRetrofit() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder().baseUrl(BaseURL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
 

public interface IService {
 
  @GET("getBestApplications.php")
    Call<List<Applications>> showAllApps();
 
}

public class MainActivity extends AppCompatActivity {
 
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_main);
  IService   iService = APIClient.getRetrofit().create(IService.class);
 
 Call<List<Application>> call = iService.showAllApps();
 
        call.enqueue(new Callback<List<Application>>() {
            @Override
            public void onResponse(Call<List<Application>> call, Response<List<Application>> response) {
            
            }
 
            @Override
            public void onFailure(<List<Application>> call, Throwable t) {
                 
            }
        });
 
    }
  
 
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="ir.androidlearn.retrofit">
  
    <uses-permission android:name="android.permission.INTERNET" />
  
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
  
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
  
</manifest>