[Spring / Async] How to invoke method in separate thread ?

[Spring / Async] How to invoke method in separate thread ? Some tasks need to be invoked in a separate thread - asynchronously. For instance when the operation needs a lot of time to finish. You just want to run it and return its id or some kind of status. In pure Java you would use Threads / Runnables and other stuff available in low-level cuncurrency API which JDK provides. Actually it isn't very convenient so Spring developers have taken care of that. I've prepared very simple Spring application which contains only two beans: RequestHandler and OperationRunner. The first one invokes the other. Here's the application runner:

    public class App {
        public static void main(final String [] args) throws InterruptedException {
            final AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
            final RequestHandler handler = context.getBean(RequestHandler.class);
            handler.handle();
        }
    }

And a configuration:

@Configuration
@ComponentScan("gt.dev.spring.async")
public class AppConfig {
}

Implementation of components:

    @Component
    public class RequestHandler {
        private static final Logger LOG = Logger.getLogger(RequestHandler.class);

        private final OperationRunner operationRunner;

        @Autowired
        public RequestHandler(final OperationRunner operationRunner) {
            this.operationRunner = operationRunner;
        }

        public void handle() throws InterruptedException {
            LOG.info("Request processing started. Invoking operation...");
            operationRunner.run();
            LOG.info("Request processed");
        }
    }

And OperationRunner:

    @Component
    public class OperationRunner {
        private static final Logger LOG = Logger.getLogger(OperationRunner.class);

        public void run() throws InterruptedException {
            LOG.info("Operation started. Sleeping...");
            Thread.sleep(5000);
            LOG.info("Operation finished");
        }
    }

After running main method in App class I get the following logs:

maj 07, 2015 3:39:28 PM gt.dev.spring.async.RequestHandler handle
INFO: Request processing started. Invoking operation...
maj 07, 2015 3:39:28 PM gt.dev.spring.async.OperationRunner run
INFO: Operation started. Sleeping...
maj 07, 2015 3:39:33 PM gt.dev.spring.async.OperationRunner run
INFO: Operation finished
maj 07, 2015 3:39:33 PM gt.dev.spring.async.RequestHandler handle
INFO: Request processed

It works as expected:

• RequestHandler logs information which indicates that process has been started
• RequestHandler invokes OperationRunner
• OperationRunner logs that operation started
• OperationRunner performs long operation (sleeps for 5 seconds)
• OperationRunner logs that operation finished
• control gets back to RequestHandler
• RequestHandler logs that request has been processed

Every client has to wait until the operation is completed. In some cases we may want to return some kind of id of operation to the client and process in the background asynchronously. Let's make the run() method async. To do that we need @Async annotation that indicates that particular method should be run in separate thread.

    @Component
    public class OperationRunner {
        private static final Logger LOG = Logger.getLogger(OperationRunner.class);

        @Async
        public void run() throws InterruptedException {
            LOG.info("Operation started. Sleeping...");
            Thread.sleep(5000);
            LOG.info("Operation finished");
        }
    }

Spring also has to know that async calls are enabled so we need one additional annotation in spring configuration - @EnableAsync. Lots of people forget about that. It's actually quite clever. You can put @Async on all the methods that need to be asynchronous and when needed disable all async calls by removing @EnableAsync.

    @Configuration
    @ComponentScan("gt.dev.spring.async")
    @EnableAsync
    public class AppConfig {
    }

After running the app I get the following log which proves that request has been processed before the async operation finished.

maj 07, 2015 3:54:13 PM gt.dev.spring.async.RequestHandler handle
INFO: Request processing started. Invoking operation...
maj 07, 2015 3:54:13 PM gt.dev.spring.async.RequestHandler handle
INFO: Request processed
maj 07, 2015 3:54:13 PM gt.dev.spring.async.OperationRunner run
INFO: Operation started. Sleeping...
maj 07, 2015 3:54:18 PM gt.dev.spring.async.OperationRunner run
INFO: Operation finished