How can I get the entity a player is looking at in a Bukkit plugin?

Question

I'm creating a wizardry plugin for Minecraft, and I was wondering how you would get the entity that a player was looking at, I know that you would have to use a Vector, but I really am not familiar with them. Pretty much what I'm looking for is something like this:

public void entityLookingAt(Player p){
    if(p.EntityLookingAt() instanceof Player){
        p.sendMessage("You're looking at a player!");
    }
}

Answer 1

Here is a method to get the entity that a player is looking at, if any at all:

public Entity getTargetEntity(Player player) {
    int r = 100;
    for (Entity entity : player.getNearbyEntities(r, r, r)) {
        if (entity instanceof LivingEntity) {
            LivingEntity livingEntity = (LivingEntity) entity;
            Location eye = player.getEyeLocation();
            Vector toEntity = livingEntity.getEyeLocation().toVector().subtract(eye.toVector());
            double dot = toEntity.normalize().dot(eye.getDirection());
            if (dot > 0.99D) {
                return entity;
            }
        }
    }
    return null;
}

Calling the method getTargetEntity(player) will return an Entity object if any is detected in the line-of-sight of the Player input parameter, or returns null if no Entity is detected.

The value of the int r near the start of the method determines how far (in blocks) to search for mobs from the player, in all directions (the x-, y-, and z-coordinates).

In this example, it is set to 100, however the method will be more accurate with higher numbers. Just remember that means more entities will be checked every time the method is run, which may eat up significant server resources.

To use in the code above, for instance, to detect if it is a Player that is being looked at, or "targeted":

public void entityLookingAt(Player p){
    if(getTargetEntity(p) instanceof Player){
        p.sendMessage("You're looking at a player!");
    }
}

This should work up to at least v1.21.1. Hopefully, this will help anyone who may have a similar question in the future.