SafeAsyncTask

源码

/** * 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 {Log.e("roboguice", "Throwable caught during background processing", t);}/** * @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 ignoredLog.e("BACKGROUND_TASK", "Exception in", f);}} catch (final Throwable t) {try {doThrowable(t);} catch (Exception f) {// logged but ignoredLog.e("BACKGROUND_TASK", "Exception in", 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 finishlatch.await();if (exceptions[0] != null) throw exceptions[0];}}}