Shooting in 8 directions

Greetings…

New problem for you guys to chew on:

In my little shooter game I control the player movement with the arrow keys, space for shooting and wasd for aiming up,down,left and right.

If the player presses the w (aim north) AND the d (aim east) keys at the same time I want the player to aim northeast.

How do I achieve that?

Right now my aiming code looks like this:

//aiming
if (Key.isDown(87)) {
this._rotation = 0;
fire();
}
if (Key.isDown(83)) {
this._rotation = 180;
fire();
}
if (Key.isDown(68)) {
this._rotation = 90;
fire();
}
if (Key.isDown(65)) {
this._rotation = 270;
fire();
}
// aiming end