Check out example codes for "android java retrofit offline cache". It will help you in understanding the concepts better.

Code Example 1

//  i.g siyanda.zama 16.05.20

in the manifest folder
<application
//dont forget to put the name
// create a java file named MyApplication.java
    android:name=".MyApplication"
    android:allowBackup="true"
    android:icon="@mipmap/launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme"
    android:usesCleartextTraffic="true"
    android:networkSecurityConfig="@xml/network_security_config">
    
in the MyApplication.java file
public class MyApplication extends Application {

    private static MyApplication instance;

    @Override
    public void onCreate() {
        super.onCreate();

        if(instance == null){
            instance = this;
        }
    }

    public static MyApplication getInstance(){
        return instance;
    }

    public static boolean hasNetwork(){
        return instance.isNetworkConnected();
    }

    private boolean isNetworkConnected(){
        ConnectivityManager cm =
                (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        return activeNetwork != null &&
                activeNetwork.isConnectedOrConnecting();
    }
}

// now finally we need to edit our okhttps
// open your api client file
OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .cache(cache())
                .addNetworkInterceptor(networkInterceptor()) // only used when network is on
                .addNetworkInterceptor(networkInterceptor()) // only used when network is on
                .addInterceptor(offlineInterceptor())
                .build();


// cache method
private static Cache cache(){
        return new Cache(new File(MyApplication.getInstance().getCacheDir(),"someIdentifier"), cacheSize);
    }

//offline network interceptor
private static Interceptor offlineInterceptor() {
        return new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Log.d(TAG, "offline interceptor: called.");
                Request request = chain.request();

                // prevent caching when network is on. For that we use the "networkInterceptor"
                if (!MyApplication.hasNetwork()) {
                    CacheControl cacheControl = new CacheControl.Builder()
                            .maxStale(7, TimeUnit.DAYS)
                            .build();

                    request = request.newBuilder()
                            .removeHeader(HEADER_PRAGMA)
                            .removeHeader(HEADER_CACHE_CONTROL)
                            .cacheControl(cacheControl)
                            .build();
                }

                return chain.proceed(request);
            }
        };
    }
//online network interceptor
 private static Interceptor networkInterceptor() {
        return new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Log.d(TAG, "network interceptor: called.");

                Response response = chain.proceed(chain.request());

                CacheControl cacheControl = new CacheControl.Builder()
                        .maxAge(5, TimeUnit.SECONDS)
                        .build();

                return response.newBuilder()
                        .removeHeader(HEADER_PRAGMA)
                        .removeHeader(HEADER_CACHE_CONTROL)
                        .header(HEADER_CACHE_CONTROL, cacheControl.toString())
                        .build();
            }
        };
    }

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