Paper PR #1986

public class TestPlugin extends JavaPlugin {
    private Mode __MODE__ = Mode.CANCEL;

    public void onEnable() {
        getServer().getPluginManager().registerEvents(new Listener() {
            @EventHandler(priority = EventPriority.MONITOR, ignoreCancelled = true)
            public void on(EntityCreatePortalEvent event) {
                System.out.println("EntityCreatePortalEvent!");
                System.out.println("   Entity Type: " + event.getEntityType());
                System.out.println("   Entity UUID: " + event.getEntity().getUniqueId());
                System.out.println("   Portal Type: " + event.getPortalType());

                switch (__MODE__) {
                    case CANCEL:
                        getServer().getOnlinePlayers().forEach(p -> p.sendMessage("Cancelled EntityCreatePortalEvent"));
                        event.setCancelled(true);
                        break;
                    case REPLACE:
                        getServer().getOnlinePlayers().forEach(p -> p.sendMessage("Replaced Blocks in EntityCreatePortalEvent"));
                        List<BlockState> blocks = event.getBlocks();
                        blocks.forEach(block -> {
                            if (block.getType() == Material.BEDROCK) {
                                block.setType(Material.BLUE_WOOL);
                                block.update(true);
                            } else if (block.getType() == Material.END_GATEWAY) {
                                block.setType(Material.YELLOW_WOOL);
                                block.update(true);
                            } else if (block.getType() == Material.END_PORTAL) {
                                block.setType(Material.PURPLE_WOOL);
                                block.update(true);
                            }
                            System.out.println("      Block: " + block.getType() + " " + block.getLocation());
                        });
                }
            }
        }, this);
    }

    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (args.length > 0) {
            try {
                __MODE__ = Mode.valueOf(args[0].toUpperCase());
                sender.sendMessage("Mode set to " + __MODE__);
                return true;
            } catch (IllegalArgumentException ignore) {
                sender.sendMessage("Unknown mode type specified!");
            }
        }
        sender.sendMessage("Current mode: " + __MODE__);
        return true;
    }

    enum Mode {
        CANCEL,
        REPLACE
    }
}