Pi4j rotary encoder reading

PI4JRotaryEncoderReading.java

// Pin pinA - CLK pin,
// Pin pinB - DT pin
// rotate(int i) - callback receiving -1 or 1

inputA = gpio.provisionDigitalInputPin(pinA, "PinA", PinPullResistance.PULL_UP);
inputB = gpio.provisionDigitalInputPin(pinB, "PinB", PinPullResistance.PULL_UP);
inputA.addListener(new GpioPinListenerDigital() {
  int lastA;

  @Override
  public synchronized void handleGpioPinDigitalStateChangeEvent(GpioPinDigitalStateChangeEvent arg0) {
    int a = inputA.getState().getValue();
    int b = inputB.getState().getValue();
    if (lastA != a) {
      rotate(b == a ? -1 : 1);
      lastA = a;	
    }
  }
});

How do I read the encoder value?

Encoder is a relative device, it doesn't store an absolute value. In your callback code, you can yourself store an int that starts at 0 and increment/decrement it each time it triggers.