How to Enable and Customize Asynchronous Execution in Spring

Enable Asynchronous Support

@Configuration
@EnableAsync
public class SpringAsyncConfig { ... }

By default, @EnableAsync detects Spring's @Async annotations and can also detect user‑defined annotation types.

Using @Async Annotation

Void return type

@Async
public void asyncMethodWithVoidReturnType() {
    System.out.println("Execute method asynchronously. " + Thread.currentThread().getName());
}

Return type (Future<String>)

@Async
public Future<String> asyncMethodWithReturnType() {
    System.out.println("Execute method asynchronously - " + Thread.currentThread().getName());
    try {
        Thread.sleep(5000);
        return new AsyncResult<String>("hello world !!!!");
    } catch (InterruptedException e) {
        // handle exception
    }
    return null;
}

Executor Configuration

Spring uses SimpleAsyncTaskExecutor by default, which has no thread‑limit. This default can be overridden at method or application level.

Method‑level override

Application‑level override

For application‑level configuration, implement AsyncConfigurer and provide a custom Executor:

@Configuration
@EnableAsync
public class SpringAsyncConfig implements AsyncConfigurer {
    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.initialize();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(25);
        return executor;
    }
}

Exception Handling

When a method returns a Future, exceptions are propagated via Future.get(). For void methods, uncaught async exceptions are lost, so a custom handler is required.

Define a handler implementing AsyncUncaughtExceptionHandler:

public class CustomAsyncExceptionHandler implements AsyncUncaughtExceptionHandler {
    @Override
    public void handleUncaughtException(Throwable throwable, Method method, Object... obj) {
        System.out.println("Exception message - " + throwable.getMessage());
        System.out.println("Method name - " + method.getName());
        for (Object param : obj) {
            System.out.println("Parameter value - " + param);
        }
    }
}

Then override getAsyncUncaughtExceptionHandler() in the configuration class to return the custom handler:

@Override
public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
    return new CustomAsyncExceptionHandler();
}