ForgeInstallWrapper.java

import java.net.URL;
import java.io.File;
import java.net.URLClassLoader;
import java.lang.reflect.Method;
import java.io.PrintStream;
import com.google.common.base.Predicate;

public class ForgeInstallWrapper {
  private static File installerJar;
  private static URLClassLoader loader;
  @SuppressWarnings("rawtypes")
  private static Class installerClass;
  private static Method runnerMethod;

  public static void main(String[] args) {
	  if (args.length == 2)
	  {
		ForgeInstall(new File(args[0]), new File(args[1]));
	  }
	  else
	  {
		System.out.println("Incorrect parameters");
	  }
  }
  
  @SuppressWarnings("unchecked")
  public static void ForgeInstall(File _installerJar, File minecraftDir) {
    installerJar = _installerJar;

    System.out.println("Installing Forge from JAR");

    try {
      URL[] jarPath = { installerJar.toURI().toURL() };
      loader = new URLClassLoader(jarPath, ForgeInstallWrapper.class.getClassLoader());
      installerClass = Class.forName("net.minecraftforge.installer.ClientInstall", true, loader);
    } catch (Throwable e) {
      e.printStackTrace();
	  System.exit(-1);
    }

    try {
      runnerMethod = installerClass.getMethod("run", File.class);
	  
	  try {
        Object instance = installerClass.newInstance();
        Object result = runnerMethod.invoke(instance, minecraftDir);
      } catch (Throwable e) {
        System.out.println("Unable to install Forge");
        System.exit(-1);
      }
	  
    } catch (Throwable e1) {
	  try {
	    runnerMethod = installerClass.getMethod("run", File.class, Predicate.class);
		Predicate<String> optPred = new Predicate<String>() {
			@Override
			public boolean apply(String s) {
				return false;
			}
		};
		
		try {
          Object instance = installerClass.newInstance();
          Object result = runnerMethod.invoke(instance, minecraftDir, optPred);
        } catch (Throwable e) {
          System.out.println("Unable to install Forge");
          System.exit(-1);
        }
		
	  } catch (Throwable e2) {
        e2.printStackTrace();
		System.exit(-1);
	  }
    }

    System.out.println("Forge update complete");
  }
}