Spring Boot Web - Sync and Async calls

Simple project to demonstrate how to execute synchronous and asynchronous tasks using Spring.

Synchronous

There is 1 synchronous task that will spend at least 5 seconds to return:

1. http://localhost:8080/sync

Simplest way to execute a task using request and request style. The request thread will block until that task is done;

Asynchronous

There are 3 asynchronous tasks that will be executed in another thread:

1. http://localhost:8080/async

Using @Async annotation and enabling that functionality with @EnableAsync, you tell Spring to execute the annotated method asynchronously. This method can return void or Future<T>. Spring will automatically manage the thread pool or you can create one implementing AsyncConfigurer.

2. http://localhost:8080/callable
3. http://localhost:8080/deferred

Deferred and Callable works almost the same way: Spring will create another thread to execute the slow process and release the thread from the originated request. However, the client connection will be waiting the response and Spring will call the Callable return or execute the Deferred when it is complete. Then return the result to the client. The main difference is that Spring will manage the thread pool when using Callable and, with Deferred, you can specify an existing ExecutorService.