Java-从命令行调用方法

Question

I want to be able to use my application through the command line. More specifically the behavior that I want to implement is this one:

If in the command line I enter the command create I want the method generateMigrationFile to be called, else if the command I entered was run I want to run my migrations( SpringApplication.run method). How can I achieve this?

My application main class

    public static void main(String[] args) {

        //if entered the command run in the command line
        //SpringApplication.run(MigrationsApplication.class, args);

        //if entered the command create in the command line
        MigrationGenerator generator=new MigrationGenerator();
        try {
            generator.generateMigrationFile("TEST");
        } catch (IOException e) {
            System.out.println("There was an error generating the file");
        }

I want to call it like:

migrationsApp run

migrationsApp create

Answer 1

The arguments you supply when executing the command line are passed on to the args parameter. So your code would look something like:

If (args.length == 0){
  System.exit(-1);
}
if (args[0].equals("run")){
// do run
} else if (args[0].equals("create"){
// do create
}

or you could use a switch statement as well.

Answer 2

You can use system argument and since you are using spring in your project you can use @Value annotation for example:

public static void main(String[] args) {

        @Value("${command}")
        final String command;
        switch(command) {
          case "run":
            SpringApplication.run(MigrationsApplication.class, args);
            break;
          case "create":
             MigrationGenerator generator=new MigrationGenerator();
             try {
                generator.generateMigrationFile("TEST");
             } catch (IOException e) {
               System.out.println("There was an error generating the file");
             }
             break;
          default:
            throw new IllegalArgumentException("Command is Invalid");
        }
}

Pass the argument as --command in command line. If you are running jar use command java -jar --command=run

Answer 3

So this is an example that shows an idea of how it can be implemented but note I'm never checking args at an exact position, useless arguments should not break the application running.

You will also notice in my example if no argument is passed it assume GUI mode, good practice so if people double click on your.JAR it loads in GUI mode. if this was CLI only app then yeah forcing an argument or arguments is fine but if you have a GUI mode use that mode as the default unless overridden by the user.

EG expected to work java -jar MyApp.jar some crap generate the argument generate is there and it should be honored.

public static void main(String[] args) {
        boolean showGui = true;
        boolean generate = false;

        for (String arg : args){
                if(arg.equals("generate")){
                        showGui = false;
                        generate = true;
                }
        }

        //if entered the command run in the command line
        if(showGui){
                SpringApplication.run(MigrationsApplication.class, args);
        }

        //if entered the command create in the command line
        if(generate){
                MigrationGenerator generator=new MigrationGenerator();
                try {
                    generator.generateMigrationFile("TEST");
                } catch (IOException e) {
                    System.out.println("There was an error generating the file");
                }
        }
}

I'm using an If because it's a simple demo with only 1 custom argument if you want to support more switch it to a switch... case statement but I would highly recommend that your run argument is not supported and by default, it falls to GUI mode