AsyncTaskResult.java

package com.claimtowers.common.asynctask;

public class AsyncTaskResult<T> {
    private T result;
    private Exception exception;

    public AsyncTaskResult(T result) {
        this.result = result;
    }

    public AsyncTaskResult(Exception exception) {
        this.exception = exception;
    }

    public T getResult() {
        return result;
    }

    public Exception getException() {
        return exception;
    }
}

Example.java

new Lova<Integer, TowerMetadata>(id -> towersHttpClient.retrieveTowerMetadata(id))
  .onSuccess(this::showTowerMetadata)
  .onError(this::displayError)
  .execute(towerId);

Lova.java

package com.claimtowers.common.asynctask;

import android.os.AsyncTask;

import java.util.function.Consumer;
import java.util.function.Function;

public class Lova<Param, Result> extends AsyncTask<Param, Void, AsyncTaskResult<Result>> {

    private final Function<Param, Result> function;
    private Consumer<Result> consumer;
    private Consumer<Exception> errorHandler;

    public Lova(Function<Param, Result> function) {
        this.function = function;
    }

    public Lova<Param, Result> onSuccess(Consumer<Result> consumer) {
        this.consumer = consumer;
        return this;
    }

    public Lova<Param, Result> onError(Consumer<Exception> errorHandler) {
        this.errorHandler = errorHandler;
        return this;
    }

    @Override
    protected AsyncTaskResult<Result> doInBackground(Param... params) {
        try {
            return new AsyncTaskResult<>(function.apply(params[0]));
        } catch (Exception e) {
            cancel(false);
            return new AsyncTaskResult<>(e);
        }
    }

    @Override
    protected void onPostExecute(AsyncTaskResult<Result> asyncTaskResult) {
        super.onPostExecute(asyncTaskResult);
        consumer.accept(asyncTaskResult.getResult());
    }

    @Override
    protected void onCancelled(AsyncTaskResult<Result> asyncTaskResult) {
        super.onCancelled(asyncTaskResult);
        errorHandler.accept(asyncTaskResult.getException());
    }
}