I use a state based singleton class for keyboard, gamepad and mouse input. The states are polled at the start for every frame.

Important is that i record the previous state - to differentiate between key down (Continues) and key press (Single key).

In my player class i can then do something like that in its update method (Jump example):

if (Input.isKeyPressed(Input.KEY_UP)) {
	if (!jumpRequested && onGround) {
		// Jump key is pressed initially
		jumpRequested = true;
		jumpForce = maxJumpForce;
	} else {
		// Jump key is hold down
		jumpForce -= stepJumpForce;
		if (jumpForce <= 0f) {
			jumpForce = 0f;
		}
	}
} else {
	if (jumpRequested) {
		// Jump key is released
		jumpRequested = false;
	}
}

// Apply force impulse when there is some jump force left
if (jumpRequested && jumpForce > 0f) {
	Vec2 f = new Vec2(0f, bodyMass * jumpForce);
	Vec2 c = body.getPosition();
	body.applyLinearImpulse(f, c, true);
}

You might take a look at the article "Designing a Robust Input Handling System for Games" and the accompanying demo (linked at the bottom of the article).

I wrote up something about this for Java:

http://www.gamedev.net/page/resources/_/technical/general-programming/java-games-keyboard-and-mouse-r2439

BTW, I'm a huge fan of do-it-yourself in Java. :-)