Passing commands to a running app from command-line

I have a Java-app (Spring Boot) that is running permanently.

I need to pass arguments and commands to it - not directly at startup but during lifetime.

E.g. empty logs or reopen database

I like to do this from a Linux commandline.

What are some of the ways this can be achieved?

I can think of having a web-handler and using console web-clients (e.g. curl) or using files that the app reads in.

You can use Spring Shell for this in Spring Boot

First, add the Spring Shell Dependency

<dependency>
<groupId>org.springframework.shell</groupId>
<artifactId>spring-shell-starter</artifactId>
</dependency>

Then, add enable the interactive shell in your applicaion.properties

spring.shell.interactive.enabled=true

or, for yaml:

spring:
  shell:
    interactive:
      enabled: true

Then, you can write you first command like so:

    @ShellComponent
    public class MyCommands {

        @ShellMethod(key = "hello-world")
        public String helloWorld(
            @ShellOption(defaultValue = "spring") String arg
        ) {
            return "Hello world " + arg;
        }
    }

When you run your spring boot application now, you can type help in the interactive shell and your command will be shown like this:

My Commands
       hello-world:

Finally, you can invoke it by typing the name of the command into the interactive shell:

shell:>hello-world
Hello world spring

shell:>hello-world --arg boot
Hello world boot