[FIXED] How does CommandLineRunner works in Spring boot

Issue

I found the below code somewhere

@SpringBootApplication
public class UsingCommandLineRunner {
    public static void main(String[] args) {
        SpringApplication.run(UsingCommandLineRunner.class);
    }

    @Bean
    public CommandLineRunner demo(){
        return (args) -> {
             // do something
        };
    }
}

How does this even working?

Who is invoking demo?

@SpringBootApplication
public class UsingCommandLineRunner {
    public static void main(String[] args) {
        SpringApplication.run(UsingCommandLineRunner.class);

        System.out.println("Args inside main()");
        for(int i=0; i<args.length; i++){
            System.out.println(args[i]);
        }
    }

    @Bean
    public CommandLineRunner demo(){
        return (args) -> {
            System.out.println("Args inside demo()");
            for(int i=0; i<args.length; i++){
                System.out.println(args[i]);
            }
            System.out.println("Using CommandLineRunner");
        };
    }
}

Upon running the above code, the below is what got printed.

Args inside demo()
Using CommandLineRunner
Args inside main()
userName=Rahul_Kumar

Why command line arguments are not inside args inside demo?

Solution

you should run this app use SpringApplication.run(UsingCommandLineRunner.class,args);

Answered By - DingHao
Answer Checked By - Candace Johnson (JavaFixing Volunteer)