@Async アノテーションで非同期メソッドの作成

package com.example.asyncmethod;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@JsonIgnoreProperties(ignoreUnknown = true)
public record User(String name, String blog) {
}

package com.example.asyncmethod;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestClient;

import java.util.concurrent.CompletableFuture;

@Service
public class GitHubLookupService {

	private static final Logger logger = LoggerFactory.getLogger(GitHubLookupService.class);

	private final RestClient restClient;

	public GitHubLookupService(RestClient.Builder restClientBuilder) {
		this.restClient = restClientBuilder.build();
	}

	@Async
	public CompletableFuture<User> findUser(String user) throws InterruptedException {
		logger.info("Looking up " + user);
		User results = restClient.get()
				.uri("https://api.github.com/users/{user}", user)
				.retrieve()
				.body(User.class);
		// Artificial delay of 1s for demonstration purposes
		Thread.sleep(1000L);
		return CompletableFuture.completedFuture(results);
	}
}

package com.example.asyncmethod;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

import java.util.concurrent.Executor;

@SpringBootApplication
@EnableAsync
public class AsyncMethodApplication {

	public static void main(String[] args) {
		// close the application context to shut down the custom ExecutorService
		SpringApplication.run(AsyncMethodApplication.class, args).close();
	}

	@Bean
	public Executor taskExecutor() {
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(2);
		executor.setMaxPoolSize(2);
		executor.setQueueCapacity(500);
		executor.setThreadNamePrefix("GithubLookup-");
		executor.initialize();
		return executor;
	}
}

package com.example.asyncmethod;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

import java.util.concurrent.CompletableFuture;

@Component
public class AppRunner implements CommandLineRunner {

	private static final Logger logger = LoggerFactory.getLogger(AppRunner.class);

	private final GitHubLookupService gitHubLookupService;

	public AppRunner(GitHubLookupService gitHubLookupService) {
		this.gitHubLookupService = gitHubLookupService;
	}

	@Override
	public void run(String... args) throws Exception {
		// Start the clock
		long start = System.currentTimeMillis();

		// Kick off multiple, asynchronous lookups
		CompletableFuture<User> page1 = gitHubLookupService.findUser("PivotalSoftware");
		CompletableFuture<User> page2 = gitHubLookupService.findUser("CloudFoundry");
		CompletableFuture<User> page3 = gitHubLookupService.findUser("Spring-Projects");

		// Wait until they are all done
		CompletableFuture.allOf(page1, page2, page3).join();

		// Print results, including elapsed time
		logger.info("Elapsed time: " + (System.currentTimeMillis() - start));
		logger.info("--> " + page1.get());
		logger.info("--> " + page2.get());
		logger.info("--> " + page3.get());

	}
}