MinecraftLauncher.java

package net.elementsmodcolab.launcherData;

import java.io.File;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Modifier;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;

public class MinecraftLauncher
{
	/**
	 * @param args
	 *            The arguments you want to launch Minecraft with. New path,
	 *            Username, Session ID.
	 */
	public static void init(String[] args)
	{
		if (args.length != 3)
		{
			System.out.println("Not enough arguments.");
			System.exit(-1);
		}

		try
		{
			System.out.println("Loading jars...");
			String[] jarFiles = new String[] {
				"minecraft.jar", "lwjgl.jar", "lwjgl_util.jar", "jinput.jar"
			};

			URL[] urls = new URL[jarFiles.length];

			for (int i = 0; i < urls.length; i++)
			{
				try
				{
					File f = new File(new File(args[0], "bin"), jarFiles[i]);
					urls[i] = f.toURI().toURL();
					System.out.println("Loading URL: " + urls[i].toString());
				} catch (MalformedURLException e)
				{
					System.err.println("MalformedURLException, " + e.toString());
					System.exit(5);
				}
			}

			System.out.println("Loading natives...");
			String nativesDir = new File(new File(args[0], "bin"), "natives").toString();

			System.setProperty("org.lwjgl.librarypath", nativesDir);
			System.setProperty("net.java.games.input.librarypath", nativesDir);

			System.setProperty("user.home", new File(args[0]).getParent());

			URLClassLoader cl = new URLClassLoader(urls, MinecraftLauncher.class.getClassLoader());

			Class<?> mc = cl.loadClass("net.minecraft.client.Minecraft");
			Field[] fields = mc.getDeclaredFields();

			for (int i = 0; i < fields.length; i++)
			{
				Field f = fields[i];
				if (f.getType() != File.class)
				{
					continue;
				}
				if (f.getModifiers() != (Modifier.PRIVATE + Modifier.STATIC))
				{
					continue;
				}
				f.setAccessible(true);
				f.set(null, new File(args[0]));

				System.out.println("Fixed Minecraft Path: Field was "
						+ f.toString());
			}

			String[] mcArgs = new String[2];
			mcArgs[0] = args[1];
			mcArgs[1] = args[2];

			String mcDir = 	mc.getMethod("a", String.class).invoke(null, (Object) "minecraft").toString();

			System.out.println("MCDIR: " + mcDir);

			mc.getMethod("main", String[].class).invoke(null, (Object) mcArgs);
		} catch (ClassNotFoundException e)
		{
			System.err.println("ClassNotFoundException, " + e.toString());
			System.exit(1);
		} catch (IllegalArgumentException e)
		{
			System.err.println("IllegalArgumentException, " + e.toString());
			System.exit(2);
		} catch (IllegalAccessException e)
		{
			System.err.println("IllegalAccessException, " + e.toString());
			System.exit(2);
		} catch (InvocationTargetException e)
		{
			System.err.println("InvocationTargetException, " + e.toString());
			System.exit(3);
		} catch (NoSuchMethodException e)
		{
			System.err.println("NoSuchMethodException, " + e.toString());
			System.exit(3);
		} catch (SecurityException e)
		{
			System.err.println("SecurityException, " + e.toString());
			System.exit(4);
		}
	}

}