Question

    public static void setMOTD(final String motd) throws Exception {
    final Field field = MinecraftServer.class.getDeclaredField("motd");
    final Field server = CraftServer.class.getDeclaredField("console");
    field.setAccessible(true);
    server.setAccessible(true);
    MinecraftServer instance = (MinecraftServer) server.get(CraftServer.class);
    field.set(instance, motd);
}

My goal with this is to change the Message of the day on a minecraft server (running craftbukkit). To do this I need to change a non-static field motd. I am doing all of this with a plugin so I can’t get the instance for the MinecraftServer. The second last line was my attempt at doing this with reflection however it failed. I don’t have access to change the MinecraftServer class or CraftServer because they are in an external library.

motd and console are both non-static fields.

motd is a String with the modifiers public final.

console is an instance of MinecraftServer with the modifiers protected final.

This is the error I’m getting (on the second last line of setMOTD):

2012-07-22 22:16:31 [SEVERE] java.lang.IllegalArgumentException: Can not set final net.minecraft.server.MinecraftServer field org.bukkit.craftbukkit.CraftServer.console to java.lang.Class

Answer 1

Solved by fetching the bukkit instance which extends CraftServer

    public static void setServerMOTD(final String motd) throws Exception {
    final Field field = MinecraftServer.class.getDeclaredField("motd");
    final Field server = CraftServer.class.getDeclaredField("console");
    Field modifiersField = Field.class.getDeclaredField("modifiers");
    modifiersField.setAccessible(true);
    field.setAccessible(true);
    server.setAccessible(true);
    modifiersField.setInt(server, server.getModifiers() & ~Modifier.FINAL);
    MinecraftServer instance = (MinecraftServer) server.get(Bukkit.getServer());
    field.set(instance, motd);
}