IProjectDescription description = project.getProject().getDescription();
ICommand[] commands = description.getBuildSpec();
ICommand[] newCommands = new ICommand[commands.length + 2];
System.arraycopy(commands, 0, newCommands, 0, commands.length);
ICommand javaCommand = description.newCommand();
javaCommand.setBuilderName("org.eclipse.jdt.core.javabuilder");
newCommands[commands.length] = javaCommand;
ICommand droolsCommand = description.newCommand();
droolsCommand.setBuilderName("org.drools.eclipse.droolsbuilder");
newCommands[commands.length + 1] = droolsCommand;
description.setBuildSpec(newCommands);
project.getProject().setDescription(description, monitor);
}