DZone
Java Zone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
  • Refcardz
  • Trend Reports
  • Webinars
  • Zones
  • |
    • Agile
    • AI
    • Big Data
    • Cloud
    • Database
    • DevOps
    • Integration
    • IoT
    • Java
    • Microservices
    • Open Source
    • Performance
    • Security
    • Web Dev
DZone > Java Zone > Google Guava Concurrency – ListenableFuture

Google Guava Concurrency – ListenableFuture

Bill Bejeck user avatar by
Bill Bejeck
·
Nov. 25, 11 · Java Zone · Interview
Like (0)
Save
Tweet
16.37K Views

Join the DZone community and get the full member experience.

Join For Free
In my last post I covered using the Monitor class from the com.google.common.util.concurrent package in the Guava Library. In this post I am going to continue my coverage of Guava concurrency utilities and discuss the ListenableFuture interface. A ListenableFuture extends the Future interface from the java.util.concurrent package, by adding a method that accepts a completion listener.

ListenableFuture

a ListenableFuture behaves in exactly the same manner as a java.util.concurrent.Future but has the method addCallback(Runnable, ExecutorService) that executes the callback in the given executor. Here is an example:

ListenableFuture futureTask = executorService.submit(callableTask)
futureTask.addListener(new Runnable() {
           @Override
           public void run() {
              ..work after futureTask completed
           }
       }, executorService);

If the submitted task has completed when you add the callback, it will run immediately. Using the addCallback method has a drawback in that the Runnable does not have access to the result produced by the future. For access to the result of the Future you would need to use a FutureCallback.

FutureCallback

A FutureCallback accepts the results produced from the Future and specifies onSuccess and onFailure methods. Here is an example:

class FutureCallbackImpl implements FutureCallback<String> {

       @Override
       public void onSuccess(String result){
            .. work with result
       }

       @Override
       public void onFailure(Throwable t) {
           ... handle exception
       }
   }

A FutureCallback is attached by using the addCallback method in the Futures class:

Futures.addCallback(futureTask, futureCallbackImpl);

At this point you may be asking how do you get an instance of ListenableFuture, when an ExecutorService only returns Futures? The answer is to use the ListenableExecutionService.

ListenableExecutionService

To use a ListenableExecutionService simply decorate an ExecutorService instance with a call to MoreExecutors.listeningDecorator(ExecutorService) for example:

ExecutorsService executorService = MoreExecutors.listeningDecorator(Executors.newCachedThreadPool());

 

Conclusion

With the ability to add a callback, whether a Runnable or the FutureCallback that handles success and failure conditions, the ListenableFuture could be a valuable addition to your arsenal. I have created a unit-test demonstrating using the ListenableFuture available as a gist. In my next post I am going to cover the Futures class, which contains static methods for working with futures.

Resources

  • Guava Project Home
  • ListenableFuture API
  • Sample Code
Google Guava Google (verb)

Opinions expressed by DZone contributors are their own.

Popular on DZone

  • Component Testing of Frontends: Karate Netty Project
  • Hyperautomation: The Beacon for Your Digital Transformation Journey
  • Progressive Delivery With Argo Rollouts: Blue-Green Deployment
  • Complete Guide to TestOps

Comments

Java Partner Resources

X

ABOUT US

  • About DZone
  • Send feedback
  • Careers
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • MVB Program
  • Become a Contributor
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 600 Park Offices Drive
  • Suite 300
  • Durham, NC 27709
  • support@dzone.com
  • +1 (919) 678-0300

Let's be friends:

DZone.com is powered by 

AnswerHub logo