This post was inspired by Creating Asynchronous Methods published at spring.io.

When dealing with RESTful services in Spring, they are relatively easy to setup. That is if you use Spring Boot. However, how do you deal with asynchronous requests. In short, how do you create a non-blocking RESTful API quickly? The easiest way is to add @Async to your methods so they are invoked asynchronously by Spring. All of this can be achieved without resorting to any methods from import java.util.concurrent.*

Setting up:

1. Create a simple Spring Boot project using this tutorial Building a RESTful Web Service
2. Add @EnableAsync to your Spring Boot Application (in the case of our example, this is Application.java)
3. Create a Service and annotate the method you wish invoke asynchronously with @Async.
4. Create the REST Controller class
5. Add the dependency to the newly created service using @Autowired
6. Create the request method (in our case this is a simple GET)
7. Call the async method
8. Run your project a SpringBoot App (Running a Spring Boot app in STS)

Add @EnableAsync to Application.java

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableAsync;

@SpringBootApplication
@EnableAsync
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Create the Service with the @Async method

package hello;

import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;

@Service
public class SampleAsyncService {
	@Async
	public void sampleAsyncMethod() {
		long time = System.currentTimeMillis();
		try {
			Thread.sleep(2000);
		} catch (InterruptedException e) {
			// We've been interrupted
			System.out.println(String.format("Task interrupted after %d milliseconds", System.currentTimeMillis() - time));
			return;
		}

		System.out.println(String.format("Task completed after %d milliseconds", System.currentTimeMillis() - time));
	}
}

Create a Rest Controller and call the Async service

package hello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class SampleAsyncController {
	@Autowired
	public SampleAsyncService sampleAsyncService;

	@RequestMapping(value = "/controller", method = RequestMethod.GET)
	@ResponseBody
	public String foo() {
		long time = System.currentTimeMillis();
		// Call Async service
		sampleAsyncService.sampleAsyncMethod();

		String response = String.format("Response completed in %d milliseconds.", (System.currentTimeMillis() - time));
		// you should see this message before the message in the async method
		System.out.println(response);

		return response;
	}
}

Source code

That's it.

/.Happy Coding