@Async for async methods in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the @Async annotation do in Spring Boot?

It marks a method to run asynchronously, meaning the method runs in a separate thread without blocking the caller.

beginner

How do you enable @Async support in a Spring Boot application?

Add <code>@EnableAsync</code> annotation to a configuration class or the main application class.

intermediate

What type of return values can an @Async method have?

It can return void, CompletableFuture, Future, or ListenableFuture to handle async results.

intermediate

Why should @Async methods be called from a different bean or class?

Because Spring proxies the bean to run async methods; calling <code>@Async</code> method from the same class bypasses the proxy and runs synchronously.

advanced

What happens if an exception is thrown inside an @Async method?

The exception is not propagated to the caller thread. You need to handle exceptions inside the async method or use a custom AsyncUncaughtExceptionHandler.

Which annotation enables asynchronous method execution in Spring Boot?

A @AsyncSupport

B @AsyncMethod

C @AsyncEnabled

D @EnableAsync

You must add @EnableAsync to enable Spring's async support.

What must you do to make a method run asynchronously using @Async?

A Annotate the method with @Async

B Call the method from the same class

C Return a String from the method

D Use @Async on the class only

Only methods annotated with @Async run asynchronously.

What is a common return type for an @Async method to handle results?

A String

B CompletableFuture

C int

D void only

@Async methods often return CompletableFuture to handle async results.

Why might calling an @Async method from the same class not run asynchronously?

A Because Spring proxies are bypassed in same-class calls

B Because @Async only works on static methods

C Because the method must be private

D Because @Async requires a return value

Spring uses proxies to run async methods; same-class calls bypass proxies.

How can you handle exceptions thrown in an @Async method?

A Use @ExceptionHandler on the method

B Exceptions automatically propagate to caller

C Use AsyncUncaughtExceptionHandler or handle inside the method

D Exceptions are ignored silently

Exceptions in async methods must be handled explicitly or via AsyncUncaughtExceptionHandler.

Explain how to set up and use @Async in a Spring Boot application.

Think about enabling async support, marking methods, and calling them properly.

Describe why calling an @Async method from the same class does not run it asynchronously and how to fix it.

Consider how Spring manages async calls with proxies.