Minecraft External Modloader

Link to minecraftforum.net-Discussion

This piece of Software allows you to manipulate the behaivior of Java-Programs by exchanging classes with your own modified ones.
Which is especially used in Minecraft-Modding and this will be the intended use for this program, but it might be possible to use this for any other java programs as well.
The normal way of exchanging classes is to open the .jar file with an archive program and replace .class files. If the jar is signed you also have to delete the META-INF folder.

This Program will not replace any .class files in any jar file, but will modify the way java loads classes to get the same result.

How to use with Minecraft

1. Install Mods
2. Download the minecraft.jar from http://minecraft.net/download ( Show all Platforms -> Minecraft for Linux/Other -> minecraft.jar )
   WARNING: This is a different minecraft.jar then the one you can find in the bin folder of your Minecraft installation!
3. Place the MinecraftExternalModloader.jar next to this minecraft.jar (the launcher, not the one in bin!)
4. Start the MinecraftExternalModloader.jar by double-clicking or with java -jar MinecraftExternalModloader.jar on the commandline This will bring up the default Mojang Minecraft-Launcher which will then hopefully launch your modded Minecraft.

How to install Mods

1. Create a folder named mod inside your Minecraft Installation Folder (%APPDATA%\.minecraft on Windows, ~/.minecraft on Linux ...)
2. Extract the mod you want to install into that folder (The parts that normally would go into the minecraft.jar)

Experts

The program contains two parts.
GenerateStartCommand generates a command-line that has all the needed parameters to launch StartMinecraft which will then inject the ReplacingClassLoader to load mods.
Run java -jar MinecraftExternalModloader.jar -dummy. To get the command-line that is generated to launch StartMinecraft.
This will output something like

javaw -Xmx1024m -Djava.library.path="/C:/Users/YourName/AppData/Roaming/.minecraft/natives" -Dsun.java2d.noddraw=true -Dsun.java2d.d3d=false -Dsun.java2d.opengl=false -Dsun.java2d.pmoffscreen=false -classpath [classpath ommitted] mapeper.minecraft.modloader.StartMinecraft file:/C:/Users/YourName/AppData/Roaming/.minecraft/mod/

on Windows 7.

file:/C:/Users/YourName/AppData/Roaming/.minecraft/mod/ is the folder the mods will get loaded from. The Inner-Program will allow you to specify multiple URLs. Even http(s) links to jar files are supported but not recommended. You can now create your personal batch/bash-Script to launch your mods.
This will skip the first step of the Minecraft-Launching

Credits

Thanks to the great Amazon-Kindle-Hacker ixtab who showed me the right technique in his JBPatcher (Source Code on bitbucket.org).
Also thanks to the MCP-Guys for making Minecraft-Modding possible.