[java] How to asynchronously call a method in Java

I've been looking at Go's goroutines lately and thought it would be nice to have something similar in Java. As far as I've searched the common way to parallelize a method call is to do something like:

final String x = "somethingelse";
new Thread(new Runnable() {
           public void run() {
                x.matches("something");             
    }
}).start();

Thats not very elegant. Is there a better way of doing this? I needed such a solution in a project so I decided to implement my own wrapper class around a async method call.

I published my wrapper class in J-Go. But I don't know if it is a good solution. The usage is simple:

SampleClass obj = ...
FutureResult<Integer> res = ...
Go go = new Go(obj);
go.callLater(res, "intReturningMethod", 10);         //10 is a Integer method parameter
//... Do something else
//...
System.out.println("Result: "+res.get());           //Blocks until intReturningMethod returns

or less verbose:

Go.with(obj).callLater("myRandomMethod");
//... Go away
if (Go.lastResult().isReady())                //Blocks until myRandomMethod has ended
    System.out.println("Method is finished!");

Internally I'm using a class that implements Runnable and do some Reflection work to get the correct method object and invoking it.

I want some opinion about my tiny library and on the subject of making async method calls like this in Java. Is it safe? Is there already a simplier way?

Java 8 introduced CompletableFuture available in package java.util.concurrent.CompletableFuture, can be used to make a asynch call :

CompletableFuture.runAsync(() -> {
    // method call or code to be asynch.
});

You may wish to also consider the class java.util.concurrent.FutureTask.

If you are using Java 5 or later, FutureTask is a turnkey implementation of "A cancellable asynchronous computation."

There are even richer asynchronous execution scheduling behaviors available in the java.util.concurrent package (for example, ScheduledExecutorService), but FutureTask may have all the functionality you require.

I would even go so far as to say that it is no longer advisable to use the first code pattern you gave as an example ever since FutureTask became available. (Assuming you are on Java 5 or later.)

You can use AsyncFunc from Cactoos:

boolean matches = new AsyncFunc(
  x -> x.matches("something")
).apply("The text").get();

It will be executed at the background and the result will be available in get() as a Future.

This is not really related but if I was to asynchronously call a method e.g. matches(), I would use:

private final static ExecutorService service = Executors.newFixedThreadPool(10);
public static Future<Boolean> matches(final String x, final String y) {
    return service.submit(new Callable<Boolean>() {

        @Override
        public Boolean call() throws Exception {
            return x.matches(y);
        }

    });
}

Then to call the asynchronous method I would use:

String x = "somethingelse";
try {
    System.out.println("Matches: "+matches(x, "something").get());
} catch (InterruptedException e) {
    e.printStackTrace();
} catch (ExecutionException e) {
    e.printStackTrace();
}

I have tested this and it works. Just thought it may help others if they just came for the "asynchronous method".

You can use Future-AsyncResult for this.

@Async
public Future<Page> findPage(String page) throws InterruptedException {
    System.out.println("Looking up " + page);
    Page results = restTemplate.getForObject("http://graph.facebook.com/" + page, Page.class);
    Thread.sleep(1000L);
    return new AsyncResult<Page>(results);
}

Reference: https://spring.io/guides/gs/async-method/

I just discovered that there is a cleaner way to do your

new Thread(new Runnable() {
    public void run() {
        //Do whatever
    }
}).start();

(At least in Java 8), you can use a lambda expression to shorten it to:

new Thread(() -> {
    //Do whatever
}).start();

As simple as making a function in JS!

i don't like the idea of using Reflection for that.
Not only dangerous for missing it in some refactoring, but it can also be denied by SecurityManager.

FutureTask is a good option as the other options from the java.util.concurrent package.
My favorite for simple tasks:

    Executors.newSingleThreadExecutor().submit(task);

little bit shorter than creating a Thread (task is a Callable or a Runnable)

You can use @Async annotation from jcabi-aspects and AspectJ:

public class Foo {
  @Async
  public void save() {
    // to be executed in the background
  }
}

When you call save(), a new thread starts and executes its body. Your main thread continues without waiting for the result of save().

Java also provides a nice way of calling async methods. in java.util.concurrent we have ExecutorService that helps in doing the same. Initialize your object like this -

 private ExecutorService asyncExecutor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());

and then call the function like-

asyncExecutor.execute(() -> {

                        TimeUnit.SECONDS.sleep(3L);}

You can use the Java8 syntax for CompletableFuture, this way you can perform additional async computations based on the result from calling an async function.

for example:

 CompletableFuture.supplyAsync(this::findSomeData)
                     .thenApply(this:: intReturningMethod)
                     .thenAccept(this::notify);

More details can be found in this article

There is also nice library for Async-Await created by EA: https://github.com/electronicarts/ea-async

From their Readme:

With EA Async

import static com.ea.async.Async.await;
import static java.util.concurrent.CompletableFuture.completedFuture;

public class Store
{
    public CompletableFuture<Boolean> buyItem(String itemTypeId, int cost)
    {
        if(!await(bank.decrement(cost))) {
            return completedFuture(false);
        }
        await(inventory.giveItem(itemTypeId));
        return completedFuture(true);
    }
}

Without EA Async

import static java.util.concurrent.CompletableFuture.completedFuture;

public class Store
{
    public CompletableFuture<Boolean> buyItem(String itemTypeId, int cost)
    {
        return bank.decrement(cost)
            .thenCompose(result -> {
                if(!result) {
                    return completedFuture(false);
                }
                return inventory.giveItem(itemTypeId).thenApply(res -> true);
            });
    }
}

It's probably not a real solution, but now - in Java 8 - You can make this code look at least a little better using lambda expression.

final String x = "somethingelse";
new Thread(() -> {
        x.matches("something");             
    }
).start();

And You could even do this in one line, still having it pretty readable.

new Thread(() -> x.matches("something")).start();