calling a jar file from within java application

[robby14]

Hi,
I am trying to use daisydiff and it provides a jar file which I easily manage to run from cmd passing it parameters (2 file names). I need to call this jar file - passing it the parameters as well, from within my java application. Is it possible please? and if yes could you guide me how I should do it?

thanks

Roberta

[travishein]

If the jar file that contains his utility with the main method is in the class path. from your code you should be able to use the reflection API to invoke the method. Get a handle on the class, and then the method, and invoke it with the string parameters that you would have used on the command line.

String mainClassName="my.package.class.Name"; // set this.
String[] args = new String[] {"param1", "param2" }; // and set the params here

//
    Class<?> mainClass = null;
    try {
      mainClass = Class.forName(mainClassName);
    }
    catch (Exception ex) {
      throw new IllegalArgumentException("class not found in your jar file " + mainClassName);
    }
    
    // ok, class loaded, now find the main method
    Method mainMethod = null;
    try {
      mainMethod = mainClass.getMethod("main", String[].class);
    }
    catch (Exception ex) {
      throw new IllegalArgumentException("class to launch (" + mainClassName + ") does not have a public static void main(String[]) method");
    }
    
    // and invoke main()
    mainMethod.invoke(null, (Object) args);

[JosAH]

If the jar file that contains his utility with the main method is in the class path. from your code you should be able to use the reflection API to invoke the method. Get a handle on the class, and then the method, and invoke it with the string parameters that you would have used on the command line.

You don't need reflection for that, you can call the main( ... ) method of that (known) class directly. If you don't know the class beforehand you indeed need reflection trickery dickery.

kind regards,

Jos

[robby14]

thanks. very useful information. I think I ll have to try the reflection thing.
thanks very much again