execute jar without a main?

Question

Can I execute a jar file without having a main class, in this way:

java -jar my_jar.jar -getX arg1 arg2 ...

Knowing that I have a method called getX with takes arg1 arg2 ... as arguments. Any idea?

Answer 1

You must have a main method.

The signature for main needs to be:

public static void main(String[] args){
    // Insert code here
}

Therefore, you can call your method getX inside the main method.

Answer 2

The short answer is no...but...

Here is a technique you can use to pass a method name and parameters on the command line when invoking the jar. This instructional example will take a method name as the 1st parameter. Tweak as necessary and add error checking/handling as needed.

package com.charles.example;
import java.lang.reflect.Method;

public class MethodRouter {

public void myMethod(final String[] args) {
    System.out.println("Amazing!! " + args[1]);
}

public static void main(String[] args) throws Exception {
    if (args.length == 0) {
        args = new String[2];
        args[0] = "myMethod";
        args[1] = "yoyo-yada-bla";
    }
    final MethodRouter methodRouter = new MethodRouter();
    final Class<?>[] types = { String[].class };
    final Class<?> _class = methodRouter.getClass();
    final String methodName = args[0];
    final Method _method = _class.getDeclaredMethod(methodName, types);
    if (_method != null) {
        _method.invoke(methodRouter, new Object[] { args });
    }
}

}

Output:

Amazing!! yoyo-yada-bla