Can Spring Boot use as command line app and as server?

Is it possible to use a Spring Boot app as a command-line application with command-line switches, as well as a server? I would like users to be able to invoke the app with command arguments, execute the desired action, and then exit.

However, I would also like the app to have the ability to start as a server and listen for REST requests. For example, for the command-line usage:

'./myapp -n:1 -b:2',

And for the server mode:

 './myapp -a:server'`,

it would start the app as a server.

Of course you can. There was a discussion for basically this topic here, but basically you can define a program argument and then create a simple if...else in main method for your needs:

public static void main(String[] args) {
    if ("n1".equals(args[0])) {
        // foo
    } else {
        SpringApplication.run(Bar.class, args);
    }
}

You've got options, you can use the SpringApplicationBuilder and based on the property you can set the web parameter to NONE/SERVLET or you could modify the incoming arguments to add a parameter so Spring Boot knows what to do. Either way should work.

public static void main(String[] args) {
  var server = ObjectUtils.containsElement(args, "-a:server");
  var type = server ? WebApplicationType.SERVLET : WebApplicationType.NONE;
  var application = new SpringApplicationBuilder()
     .sources(Bar.class)
     .web(type).build();
  application.run(args);
}

Or you could modify the incoming arguments and add spring.main.web-application-type with the value based on what you pass in.

public static void main(String[] args) {
  var server = ObjectUtils.containsElement(args, "-a:server");
  var param = "spring.main.web-application-type=" + ( server ? "SERVLET" : "NONE");
  var argsToUse = ObjectUtils.addObjectToArray(args, param);
  SpringApplication.run(Bar.class, argsToUse);
}