Hey all. Just have got an idea. So, try to explain: The plugin check, if player is connected. If connected player bought the game(http://www.minecraft.net/game/checkserver.jsp i think), then player can connect to server without problem. But if player is not bought the game, player will be checked whitelist. If this player in whitelist - he can pass, else - no. I hope you understood me guys. Thanks!
Code: If (player != bought_game) { System.out.println("Buy the Fing game!!!!"); window.open ("www.minecraft.net","Minecraft"); }