ActionHandler.java

public class ActionHandler
{
	Map<String, List<IKeyAction>> actions = new HashMap<String, List<IKeyAction>>();
	
	/**
	 * 
	 * @param alias 
	 * @param action Implementation of {@link IKeyAction}, or a lambda expression of {@link IKeyAction#run(EntityPlayer)}
	 */
	public void registerKeyAction(String alias, IKeyAction action)
	{
		if(this.actions.containsKey(alias))
		{
			this.actions.get(alias).add(action);
		}
		else
		{
			List<IKeyAction> newKeybind = new ArrayList<IKeyAction>();
			newKeybind.add(action);
			this.actions.put(alias, newKeybind);
		}
	}
	
	protected void doAction(String alias, EntityPlayer player)
	{
		if(this.actions.containsKey(alias))
		{
			List<IKeyAction> list = this.actions.get(alias);
			if(!list.isEmpty())
			{
				for(IKeyAction action : list)
				{
					action.run(player);
				}
			}
		}
	}
}

IKeyAction.java

@FunctionalInterface
public interface IKeyAction
{
	void run(EntityPlayer player);
}

KeyHandler.java

public class KeyHandler
{
	private static KeyHandler INSTANCE = new KeyHandler();
	HashMap<KeyBinding, String> aliases = new HashMap<KeyBinding, String>();
	
	public KeyHandler()
	{
		GameSettings gs = Minecraft.getMinecraft().gameSettings;
		this.aliases.put(gs.keyBindAttack,              ATTACK);
		this.aliases.put(gs.keyBindUseItem,             PLACE);
		this.aliases.put(gs.keyBindPickBlock,           PICK);
		this.aliases.put(gs.keyBindDrop,                DROP);
		this.aliases.put(gs.keyBindsHotbar[0],          SLOT1);
		this.aliases.put(gs.keyBindsHotbar[1],          SLOT2);
		this.aliases.put(gs.keyBindsHotbar[2],          SLOT3);
		this.aliases.put(gs.keyBindsHotbar[3],          SLOT4);
		this.aliases.put(gs.keyBindsHotbar[4],          SLOT5);
		this.aliases.put(gs.keyBindsHotbar[5],          SLOT6);
		this.aliases.put(gs.keyBindsHotbar[6],          SLOT7);
		this.aliases.put(gs.keyBindsHotbar[7],          SLOT8);
		this.aliases.put(gs.keyBindsHotbar[8],          SLOT9);
		this.aliases.put(gs.keyBindInventory,           INVENTORY);
		this.aliases.put(gs.keyBindSwapHands,           SWAPHANDS);
		this.aliases.put(gs.keyBindSpectatorOutlines,   HIGHLIGHT);
		this.aliases.put(gs.keyBindScreenshot,          SCREENSHOT);
		this.aliases.put(gs.keyBindSmoothCamera,        CINEMATIC);
		this.aliases.put(gs.keyBindFullscreen,          FULLSCREEN);
		this.aliases.put(gs.keyBindTogglePerspective,   PERSPECTIVE);
		this.aliases.put(gs.keyBindJump,                JUMP);
		this.aliases.put(gs.keyBindSneak,               SNEAK);
		this.aliases.put(gs.keyBindSprint,              SPRINT);
		this.aliases.put(gs.keyBindLeft,                LEFT);
		this.aliases.put(gs.keyBindRight,               RIGHT);
		this.aliases.put(gs.keyBindBack,                BACK);
		this.aliases.put(gs.keyBindForward,             FORWARD);
		this.aliases.put(gs.keyBindPlayerList,          LIST);
		this.aliases.put(gs.keyBindChat,                CHAT);
		this.aliases.put(gs.keyBindCommand,             COMMAND);
	}
	
	public static KeyHandler getHandler()
	{
		return INSTANCE;
	}
	
	/**
	 * Register any keybinds your mod adds with Sapphire's key handling system
	 * @param alias Alias for your keybind, for example keyBindJump is aliased with "jump"
	 * @param keyBinding Keybind to associate this alias with   
	 */
	public void registerKeybindAlias(String alias, KeyBinding keyBinding)
	{
		if(!this.aliases.containsValue(alias))
		{
			this.aliases.put(keyBinding, alias);
		}
	}
	
	@SubscribeEvent
	public void tick(TickEvent.PlayerTickEvent event)
	{
		for(KeyBinding k : Minecraft.getMinecraft().gameSettings.keyBindings)
		{
			if(k.isKeyDown())
			{
				Sapphire.SNW.sendToServer(new PacketDoAction(event.player.getEntityId(), this.aliases.get(k)));
			}
		}
	}
}

KeyReference.java

public class KeyReference
{
	public static final String
			ATTACK = "attack",
			PLACE = "place",
			PICK = "pick",
			DROP = "drop",
			SLOT1 = "slot1",
			SLOT2 = "slot2",
			SLOT3 = "slot3",
			SLOT4 = "slot4",
			SLOT5 = "slot5",
			SLOT6 = "slot6",
			SLOT7 = "slot7",
			SLOT8 = "slot8",
			SLOT9 = "slot9",
			INVENTORY = "inventory",
			SWAPHANDS = "swaphands",
			HIGHLIGHT = "highlight",
			SCREENSHOT = "screenshot",
			CINEMATIC = "cinematic",
			FULLSCREEN = "fullscreen",
			PERSPECTIVE = "perspective",
			JUMP = "jump",
			SNEAK = "sneak",
			SPRINT = "sprint",
			LEFT = "left",
			RIGHT = "right",
			BACK = "back",
			FORWARD = "forward",
			LIST = "list",
			CHAT = "chat",
			COMMAND = "command";
}

PacketDoAction.java

public class PacketDoAction implements IMessage
{
	String alias;
	int entityId;
	
	public PacketDoAction(){}
	
	public PacketDoAction(int entityId, String alias)
	{
		this.entityId = entityId;
		this.alias = alias;
	}
	
	@Override
	public void toBytes(ByteBuf buf)
	{
		buf.writeInt(this.alias.getBytes().length);
		buf.writeBytes(this.alias.getBytes());
		buf.writeInt(this.entityId);
	}
	
	@Override
	public void fromBytes(ByteBuf buf)
	{
		int length = buf.readInt();
		this.alias = buf.readBytes(length).toString(StandardCharsets.UTF_8);
		this.entityId = buf.readInt();
	}
	
	public static final class DoActionHandler implements IMessageHandler<PacketDoAction, IMessage>
	{
		@Override
		public IMessage onMessage(PacketDoAction message, MessageContext ctx)
		{
			if(ctx.getServerHandler().playerEntity.worldObj.getEntityByID(message.entityId) != null && ctx.getServerHandler().playerEntity.worldObj.getEntityByID(message.entityId) instanceof EntityPlayer)
			{
				EntityPlayer player = (EntityPlayer)ctx.getServerHandler().playerEntity.worldObj.getEntityByID(message.entityId);
				Sapphire.ACTIONHANDLER.doAction(message.alias, player);
			}
			return null;
		}
	}
}

RegisterKeybinds.java

public class RegisterKeybinds
{
	public static void register()
	{
		Sapphire.ACTIONHANDLER.registerKeyAction(KeyReference.JUMP, (player) ->
		{
			if(FMLCommonHandler.instance().getMinecraftServerInstance().isFlightAllowed())
			{
				player.motionY += 0.115;
				if(player.motionY > 0.4)
				{
					player.motionY = 0.4;
				}
				player.fallDistance = 0f;
				player.velocityChanged = true;
			}
		});
		
		//Sapphire.ACTIONHANDLER.registerKeyAction(...
	}
}