public class MainClass extends JavaPlugin {
    @Override
    public void onEnable ( ) {
       PacketEventManager eventManager = PacketInjectorPlugin. getInstance ( ). getPacketInjectorAPI ( ). getEventManager ( ) ;
       eventManager. registerPacketReceiveListener ( this, event -> {
            if (event. getPacketName ( ). equals ( "PacketPlayInChat" ) ) {
                String message = ( String ) event. getValue ( "a" ) ; // Might change between mc versions

                if (message. contains ( "bannedWord" ) ) {
                   event. setCancelled ( true ) ;
                   event. getPlayer ( ). sendMessage ( "§cDon't swear!" ) ;
                }
            }
        } ) ;
    }
}