Spring 3: How to call @Async annotated methods from the TaskExecutor

Question

I'm new to asynchronous task execution in Spring, so please forgive me if this sounds like a silly question.

I read that @Async annotation is introduced from Spring 3.x onward at method level to invocation of that method will occur asynchronously. I also read that we can configure the ThreadPoolTaskExecutor in the spring config file.

What I'm not able to understand is that how to call a @Async annotated method from a tak executor lets suppose - AsyncTaskExecutor

Earlier we used to do something like in a class:

@Autowired protected AsyncTaskExecutor executor;

And then

executor.submit(<Some Runnable or Callable task>)

I'm not able to understand the relationship between @Async annotated methods and TaskExecutor.

I tried searching a lot over the internet but could not get anything on this.

Can somebody provide an example for the same.

Answer 1

Complete Example

1. Config Spring

   @Configuration        
   @EnableAsync        
   @ComponentScan("com.async")
   public class AppConfig {
   
       @Bean
       public AsyncManager asyncManger() {
           return new AsyncManager();
       }
   
       @Bean
       public AsyncExecutor asyncExecutor() {
           return new AsyncExecutor();
       }
   }
   

2. Executor Class Created, Executor i have created so that spring takes care of thread management.

   public class AsyncExecutor extends AsyncConfigurerSupport {
   
       @Override
       public Executor getAsyncExecutor() {
           ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
           executor.setCorePoolSize(2);
           executor.setMaxPoolSize(2);
           executor.setQueueCapacity(500);
           executor.setThreadNamePrefix("Violation-");
           executor.initialize();
           return executor;
       }
   }
   

3. Create a manager.

   public class AsyncManager {
   
       @Autowired
       private AsyncService asyncService;
   
       public void doAsyncTask(){
           try {
               Map<Long, ViolationDetails> violation = asyncService.getViolation();
               if(!org.springframework.util.CollectionUtils.isEmpty(violation)){
                   violation.entrySet().forEach( violationEntry -> {System.out.println(violationEntry.getKey() +"" +violationEntry.getValue());});
               }
               System.out.println("do some async task");
           } catch (Exception e) {
           }
   
       }
   }
   

4. Configure your service class.

   @Service
   public class AsyncService {
   
       @Autowired
       private AsyncExecutor asyncExecutor;
   
       @Async
       public Map<Long,ViolationDetails> getViolation() {
           // TODO Auto-generated method stub
           List<Long> list = Arrays.asList(100l,200l,300l,400l,500l,600l,700l);
           Executor executor = asyncExecutor.getAsyncExecutor();
           Map<Long,ViolationDetails>  returnMap = new HashMap<>();
           for(Long estCode : list){
               ViolationDetails violationDetails = new ViolationDetails(estCode);
               returnMap.put(estCode, violationDetails);
               executor.execute((Runnable)new ViolationWorker(violationDetails));
           }
           return returnMap;       
       }
   }
   class ViolationWorker implements Runnable{
   
       private ViolationDetails violationDetails;
   
       public ViolationWorker(ViolationDetails violationDetails){
           this.violationDetails = violationDetails;
       }
   
       @Override
       public void run() {
           violationDetails.setViolation(System.currentTimeMillis());
           System.out.println(violationDetails.getEstablishmentID() + "    " + violationDetails.getViolation());
       }
   }
   

5. Model.

   public class ViolationDetails {
       private long establishmentID;
       private long violation;
   
   
       public ViolationDetails(long establishmentID){
           this.establishmentID = establishmentID;
       }
   
       public long getEstablishmentID() {
           return establishmentID;
       }
       public void setEstablishmentID(long establishmentID) {
           this.establishmentID = establishmentID;
       }
       public long getViolation() {
           return violation;
       }
       public void setViolation(long violation) {
           this.violation = violation;
       }
   
   }
   

6. Test to Run

   public class AppTest {
       public static void main(String[] args) throws SQLException {
           AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
           ctx.register(AppConfig.class);
           ctx.refresh();
   
           AsyncManager task= ctx.getBean(AsyncManager.class);
           task.doAsyncTask();
       }
   }
   

Answer 2

Here's an example of @Async use:

@Async
void doSomething() {
    // this will be executed asynchronously
}

Now call that method from another class and it will run asynchronously. If you want a return value use a Future

@Async
Future<String> returnSomething(int i) {
    // this will be executed asynchronously
}

The relationship between @Async and TaskExecutor is that @Async uses a TaskExecutor behind the scenes. From the docs:

By default when specifying @Async on a method, the executor that will be used is the one supplied to the 'annotation-driven' element as described above. However, the value attribute of the @Async annotation can be used when needing to indicate that an executor other than the default should be used when executing a given method.

So to set up a default executor, add this to your spring config

<task:annotation-driven executor="myExecutor" />

Or to use a particular executor for a single use try

@Async("otherExecutor")

See http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/scheduling.html#scheduling-annotation-support-async