AsyncTask

AsyncTaskExample.java

package rodgarcialima.task;

public class AsyncTaskActivity {
    private void download() {
      new Task1<Integer, List<Product>>(
              top -> { // receive 10 here
                  Response<List<Product>> response = apiService.getProducts(top).execute();
                  if (response.isSuccessful()) {
                      return response.body();
                  }
                  return new ArrayList<>();
              },
              result -> {
                  productsAdapter = new ProductsAdapter(result, MainActivity.this);
                  recyclerView.setAdapter(productsAdapter);
              },
              error -> Toast.makeText(MainActivity.this, "Error: " + error.getMessage(), Toast.LENGTH_SHORT).show()
      ).execute(10); // return top 10 products
    }
}

Task1.java

package rodgarcialima.task;

import android.os.AsyncTask;

public class Task1<Param, Result> extends AsyncTask<Param, Void, Result> {
    private TaskExecutor<Param, Result> taskExecutor;
    private TaskResult<Result> taskResult;
    private TaskError taskError;
    private Throwable throwable = null;

    public Task1(TaskExecutor<Param, Result> taskExecutor,
                 TaskResult<Result> taskResult,
                 TaskError taskError) {
        this.taskExecutor = taskExecutor;
        this.taskResult = taskResult;
        this.taskError = taskError;
    }

    @Override
    protected Result doInBackground(Param[] params) {
        Result res = null;
        try {
            res = this.taskExecutor.onExecute(params[0]);
        } catch (Throwable throwable) {
            this.throwable = throwable;
        }
        return res;
    }

    @Override
    protected void onPostExecute(Result result) {
        // If we have an error
        if (this.throwable != null) {
            this.taskError.onError(this.throwable);
            return;
        }

        // All good
        this.taskResult.onResult(result);
    }
}

Task2.java

package rodgarcialima.task;

import android.os.AsyncTask;

public class Task2<Param, Progress, Result> extends AsyncTask<Param, Progress, Result> {
    private TaskExecutor<Param, Result> taskExecutor;
    private TaskProgress<Progress> taskProgress;
    private TaskResult<Result> taskResult;
    private TaskError taskError;
    private Throwable throwable = null;

    public Task2(TaskExecutor<Param, Result> taskExecutor,
                 TaskProgress<Progress> taskProgress,
                 TaskResult<Result> taskResult,
                 TaskError taskError) {
        this.taskExecutor = taskExecutor;
        this.taskProgress = taskProgress;
        this.taskResult = taskResult;
        this.taskError = taskError;
    }

    @Override
    protected Result doInBackground(Param[] params) {
        Result res = null;
        try {
            res = this.taskExecutor.onExecute(params[0]);
        } catch (Throwable throwable) {
            this.throwable = throwable;
        }
        return res;
    }

    @Override
    protected void onPostExecute(Result result) {
        // If we have an error
        if (this.throwable != null) {
            this.taskError.onError(this.throwable);
            return;
        }

        // All good
        this.taskResult.onResult(result);
    }

    @Override
    protected void onProgressUpdate(Progress[] progress) {
        if (this.taskProgress != null) {
            this.taskProgress.onProgress(progress[0]);
        }
    }
}

TaskError.java

package rodgarcialima.task;

public interface TaskError {
    void onError(Throwable error);
}

TaskExecutor.java

package rodgarcialima.task;

public interface TaskExecutor<Param, Result> {
    Result onExecute(Param param) throws Throwable;
}

TaskProgress.java

package rodgarcialima.task;

public interface TaskProgress<T> {
    void onProgress(T progress);
}

TaskResult.java

package rodgarcialima.task;

public interface TaskResult<Result> {
    void onResult(Result result);
}