Guava - Parallel Programming Futures Details

Guava provides many useful extensions for Java parallel programming Future, its main interface is ListenableFuture, and it extends statically with the help of Futures.

ListenableFuture inherited to Future allows us to add a callback function to return the value when the thread operation is completed or the method execution is returned immediately.

Add a callback function to ListenableFuture:

Futures.addCallback(ListenableFuture<V>, FutureCallback<V>, Executor)

Where FutureCallback is an interface containing onSuccess(V) and onFailure(Throwable).

Used as follows:

 Futures.addCallback(ListenableFuture, new FutureCallback<Object>() { public void onSuccess(Object result) { System.out.printf("onSuccess with: %s%n", result); } public void onFailure(Throwable thrown) { System.out.printf("onFailure %s%n", thrown.getMessage()); }});

At the same time, Futures in Guava also has:

1. transform: converts the return value of ListenableFuture.
2. allAsList: A merge of multiple ListenableFutures, returning a List object that returns multiple Future return values ​​when all Futures succeed. Note: When one of the Future fails or cancels, it will enter failure or cancel.
3. successfulAsList: Similar to allAsList, the only difference is that the future return value that fails or cancels is replaced by null. The process will not be failed or cancelled.
4. immediateFuture/immediateCancelledFuture: Returns a ListenableFuture that is to be returned immediately.
5. makeChecked: Convert ListenableFuture to CheckedFuture. CheckedFuture is a ListenableFuture that contains multiple versions of the get method, which declares throws check exceptions. This makes it easier to create a Future that can throw exceptions in the execution logic.
6. JdkFutureAdapters.listenInPoolThread(future): guava also provides an interface function to convert JDK Future to ListenableFuture.
   

Below is a test demo for Future:

 @Testpublic void should_test_furture() throws Exception { ListeningExecutorService service = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10)); ListenableFuture future1 = service.submit(new Callable<Integer>() { public Integer call() throws InterruptedException { Thread.sleep(1000); System.out.println("call future 1."); return 1; } }); ListenableFuture future2 = service.submit(new Callable<Integer>() { public Integer call() throws InterruptedException { Thread.sleep(1000); System.out.println("call future 2."); // throw new RuntimeException("----call future 2."); return 2; } }); final ListenableFuture allFuture = Futures.allAsList(future1, future2); final ListenableFuture transform = Futures.transform(allFutures, new AsyncFunction<List<Integer>, Boolean>() { @Override public ListenableFuture apply(List<Integer> results) throws Exception { return Futures.immediateFuture(String.format("success future:%d", results.size())); } }); Futures.addCallback(transform, new FutureCallback<Object>() { public void onSuccess(Object result) { System.out.println(result.getClass()); System.out.printf("success with: %s%n", result); } public void onFailure(Throwable thrown) { System.out.printf("onFailure%s%n", thrown.getMessage()); } }); System.out.println(transform.get());}

Official information homepage: https://awk.so/@code.google.com!/p/guava-libraries/wiki/ListenableFutureExplained

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