如何从主应用程序调用服务调用 Spring Boot？

Question

I'm building a Spring Boot application that will be called from command line. I will pass to application some parameters but I'm having problems to call a service from this class:

@SpringBootApplication
public class App{

    public static void main(String[] args) {

        SpringApplication.run(App.class, args);

        App app = new App();
        app.myMethod();    
    }

    @Autowired
    private MyService myService;

    private void myMethod(){
        myService.save();
    }
}

I'm trying to call a method from inside the main but I'm getting the error:

Exception in thread "main" java.lang.NullPointerException
at com.ef.Parser.App.myMethod(Application.java:26)
at com.ef.Parser.App.main(Application.java:18)

Answer 1

you can create a class that implements CommandLineRunner and this will be invoked after the app will start

@Component
public class CommandLineAppStartupRunner implements CommandLineRunner {
    @Autowired
    private MyService myService;

    @Override
    public void run(String...args) throws Exception {
       myService.save();

    }
}

you can get farther information on this here

Answer 2

In SpringBoot 2.x you can simply run the application by SpringApplication.run method and operate on the returned ApplicationContext. Complete example below:

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Service;
import java.util.Arrays;

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        ApplicationContext applicationContext = SpringApplication.run(DemoApplication.class, args);
        SomeService service = applicationContext.getBean(SomeService.class);
        service.doSth(args);
    }
}

@Service
class SomeService {

    public void doSth(String[] args){
        System.out.println(Arrays.toString(args));
    }
}

Answer 3

By using the new keyword yourself to create an instance of the App class, Spring cannot know about it.

It's also redundant, as Spring automatically creates a bean instance of this class by a mechanism called component scan.

I like the solution of the CommandLineRunner .

What you also can do, is retrieve the ApplicationContext , lookup the bean and then call the method.

You can inject the ApplicationContext by letting your App class implement ApplicationContextAware , override the setter method and save the context in a static variable which you can access from your main method.

Then, you can use it to retrieve the correct App instance.

App myApp = (App) applicationContext.getBean(App.class);
myApp.myMethod()

Please note that accessing the ApplicationContext directly does kind of violate the whole dependency injection principle, but sometimes you haven't got much choice.

Answer 4

The issue with your code is you didn't look up the applicationContext bean for the service Which you are using. I had a similar use case, to call a feature service on the startup of the application. Initializing multiple applicationContext beans for the services and then making the method called works just fine! Code below :

public static void main(String[] args) {
    ApplicationContext applicationContext = SpringApplication.run(UamRbacApplication.class, args);
    AccessChangeSchedulerService accessChangeSchedulerService = applicationContext.getBean(AccessChangeSchedulerService.class);
    AppContext appContext = applicationContext.getBean(AppContext.class);
    try {
        accessChangeSchedulerService.fetchAccessLevelChanges("EP", appContext.getSplunkToken());
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
}

Cheers.