Spring - CommandLineRunner interface

CommandLineRunner interface

Interface used to indicate that a bean should run when it is contained within a SpringApplication. Multiple CommandLineRunner beans can be defined within the same application context and can be ordered using the Ordered interface or @Order annotation.

CommandLineRunner is a simple Spring Boot interface with a run method. Spring Boot will automatically call the run method of all beans implementing this interface after the application context has been loaded.

The run method is called after the application context is loaded, but before the execution of the main method is complete.

https://github.com/explorer436/programming-playground/tree/main/java-playground/springboot-commandlinerunner-example

Implementation that uses a separate Component

The method doesn’t always have to go into the main class. It can also be in a separate class.

e.g.

import com.example.enable_async_in_springboot_demo.model.User;
import com.example.enable_async_in_springboot_demo.service.GitHubLookupService;
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 of 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());

    }

}