Android Open Source - Teracast-Android Safe Async Task

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License

The source code is released under:
Apache License
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Java Source Code

package com.davidtpate.teracast.util;
//w  w w. j  a  v a 2 s .  co m
import android.os.Handler;
import android.os.Looper;
import java.io.InterruptedIOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.concurrent.Callable;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;

/**
 * Originally from RoboGuice: https://github.com/roboguice/roboguice/blob/master/roboguice/src/main/java/roboguice/util/SafeAsyncTask.java
 * <p/>
 * A class similar but unrelated to android's {@link android.os.AsyncTask}.
 * <p/>
 * Unlike AsyncTask, this class properly propagates exceptions.
 * <p/>
 * If you're familiar with AsyncTask and are looking for {@link android.os.AsyncTask#doInBackground(Object[])}, we've
 * named it {@link #call()} here to conform with java 1.5's {@link java.util.concurrent.Callable} interface.
 * <p/>
 * Current limitations: does not yet handle progress, although it shouldn't be hard to add.
 * <p/>
 * If using your own executor, you must call future() to get a runnable you can execute.
 *
 * @param <ResultT>
 */
public abstract class SafeAsyncTask<ResultT> implements Callable<ResultT> {
  public static final    int      DEFAULT_POOL_SIZE = 25;
  protected static final Executor DEFAULT_EXECUTOR  = Executors.newFixedThreadPool(DEFAULT_POOL_SIZE);

  protected Handler             handler;
    protected Executor            executor;
    protected StackTraceElement[] launchLocation;
    protected FutureTask<Void>    future;

    /**
     * Sets executor to Executors.newFixedThreadPool(DEFAULT_POOL_SIZE) and Handler to new Handler()
     */
    public SafeAsyncTask() {
        this.executor = DEFAULT_EXECUTOR;
    }

    /**
     * Sets executor to Executors.newFixedThreadPool(DEFAULT_POOL_SIZE)
     */
    public SafeAsyncTask(Handler handler) {
        this.handler = handler;
        this.executor = DEFAULT_EXECUTOR;
    }

    /**
     * Sets Handler to new Handler()
     */
    public SafeAsyncTask(Executor executor) {
        this.executor = executor;
    }

    public SafeAsyncTask(Handler handler, Executor executor) {
        this.handler = handler;
        this.executor = executor;
    }

    public FutureTask<Void> future() {
        future = new FutureTask<Void>(newTask());
        return future;
    }

    public SafeAsyncTask<ResultT> executor(Executor executor) {
        this.executor = executor;
        return this;
    }

    public Executor executor() {
        return executor;
    }

    public SafeAsyncTask<ResultT> handler(Handler handler) {
        this.handler = handler;
        return this;
    }

    public Handler handler() {
        return handler;
    }

    public void execute() {
        execute(Thread.currentThread().getStackTrace());
    }

    protected void execute(StackTraceElement[] launchLocation) {
        this.launchLocation = launchLocation;
        executor.execute(future());
    }

    public boolean cancel(boolean mayInterruptIfRunning) {
    if (future == null) {
      throw new UnsupportedOperationException("You cannot cancel this task before calling future()");
    }

    return future.cancel(mayInterruptIfRunning);
  }

  /**
   * @throws Exception,
   *     captured on passed to onException() if present.
   */
  protected void onPreExecute() throws Exception {
  }

  /**
   * @param t
   *     the result of {@link #call()}
   *
   * @throws Exception,
   *     captured on passed to onException() if present.
   */
  @SuppressWarnings({"UnusedDeclaration"})
  protected void onSuccess(ResultT t) throws Exception {
  }

  /**
   * Called when the thread has been interrupted, likely because the task was canceled.
   * <p/>
   * By default, calls {@link #onException(Exception)}, but this method may be overridden to handle interruptions
   * differently than other exceptions.
   *
   * @param e
   *     an InterruptedException or InterruptedIOException
   */
  protected void onInterrupted(Exception e) {
    onException(e);
  }

  /**
   * Logs the exception as an Error by default, but this method may be overridden by subclasses.
   *
   * @param e
   *     the exception thrown from {@link #onPreExecute()}, {@link #call()}, or {@link #onSuccess(Object)}
   *
   * @throws RuntimeException,
   *     ignored
   */
  protected void onException(Exception e) throws RuntimeException {
    onThrowable(e);
  }

  protected void onThrowable(Throwable t) throws RuntimeException {
    Ln.e(t, "Throwable caught during background processing");
  }

  /**
   * @throws RuntimeException,
   *     ignored
   */
  protected void onFinally() throws RuntimeException {
  }

  protected Task<ResultT> newTask() {
    return new Task<ResultT>(this);
  }

  public static class Task<ResultT> implements Callable<Void> {
    protected SafeAsyncTask<ResultT> parent;
    protected Handler handler;

        public Task(SafeAsyncTask<ResultT> parent) {
            this.parent = parent;
            this.handler = parent.handler != null ? parent.handler : new Handler(Looper.getMainLooper());
        }

        public Void call() throws Exception {
            try {
                doPreExecute();
                doSuccess(doCall());
            } catch (final Exception e) {
                try {
                    doException(e);
                } catch (Exception f) {
                    // logged but ignored
                    Ln.e(f);
                }
            } catch (final Throwable t) {
                try {
                    doThrowable(t);
                } catch (Exception f) {
                    // logged but ignored
                    Ln.e(f);
                }
            } finally {
                doFinally();
            }

            return null;
        }

        protected void doPreExecute() throws Exception {
            postToUiThreadAndWait(new Callable<Object>() {
                public Object call() throws Exception {
                    parent.onPreExecute();
                    return null;
                }
            });
        }

        protected ResultT doCall() throws Exception {
            return parent.call();
        }

        protected void doSuccess(final ResultT r) throws Exception {
            postToUiThreadAndWait(new Callable<Object>() {
                public Object call() throws Exception {
                    parent.onSuccess(r);
                    return null;
                }
            });
        }

        protected void doException(final Exception e) throws Exception {
            if (parent.launchLocation != null) {
                final ArrayList<StackTraceElement> stack = new ArrayList<StackTraceElement>(Arrays.asList(e.getStackTrace()));
                stack.addAll(Arrays.asList(parent.launchLocation));
                e.setStackTrace(stack.toArray(new StackTraceElement[stack.size()]));
            }
            postToUiThreadAndWait(new Callable<Object>() {
                public Object call() throws Exception {
                    if (e instanceof InterruptedException || e instanceof InterruptedIOException) {
                        parent.onInterrupted(e);
                    } else {
                        parent.onException(e);
                    }
                    return null;
                }
            });
        }

        protected void doThrowable(final Throwable e) throws Exception {
            if (parent.launchLocation != null) {
                final ArrayList<StackTraceElement> stack = new ArrayList<StackTraceElement>(Arrays.asList(e.getStackTrace()));
                stack.addAll(Arrays.asList(parent.launchLocation));
                e.setStackTrace(stack.toArray(new StackTraceElement[stack.size()]));
            }
            postToUiThreadAndWait(new Callable<Object>() {
                public Object call() throws Exception {
                    parent.onThrowable(e);
                    return null;
                }
            });
        }

        protected void doFinally() throws Exception {
            postToUiThreadAndWait(new Callable<Object>() {
                public Object call() throws Exception {
                    parent.onFinally();
                    return null;
                }
            });
        }

        /**
         * Posts the specified runnable to the UI thread using a handler, and waits for operation to finish.  If there's
         * an exception, it captures it and rethrows it.
         *
         * @param c
         *     the callable to post
         *
         * @throws Exception
         *     on error
         */
        protected void postToUiThreadAndWait(final Callable c) throws Exception {
            final CountDownLatch latch = new CountDownLatch(1);
            final Exception[] exceptions = new Exception[1];

            // Execute onSuccess in the UI thread, but wait
            // for it to complete.
            // If it throws an exception, capture that exception
            // and rethrow it later.
            handler.post(new Runnable() {
                public void run() {
                    try {
                        c.call();
                    } catch (Exception e) {
                        exceptions[0] = e;
                    } finally {
                        latch.countDown();
                    }
                }
            });

            // Wait for onSuccess to finish
            latch.await();

            if (exceptions[0] != null) {
                throw exceptions[0];
            }
        }
    }
}
Java Source Code List
