How to filter on Apache Edgent and also show the values which were filtered?

Question

I am using Apache Edgent (Java framework) to poll values from a HCSR04 ultrasonic sensor on a Raspberry Pi every 3 seconds. I use a filter to not get values from 50cm to 80cm.

    UltrasonicStream sensor = new UltrasonicStream();
    DirectProvider dp = new DirectProvider();
    Topology topology = dp.newTopology();
    TStream<Double> tempReadings = topology.poll(sensor, 3, TimeUnit.SECONDS);
    TStream<Double> filteredReadings = tempReadings.filter(reading -> reading < 50 || reading > 80);
    System.out.println("filter added: tempReadings.filter(reading -> reading < 50 || reading > 80);");
    filteredReadings.print();
    dp.submit(topology);

I want to show some message when the values are filtered. When the values do not match with my filter I can poll them, but when they match I am not returning, that is ok. However, I want just to show that a value was filtered using Apache Edgent libraries. I know that I can do something on the public double get() method, but I wonder if I could do this trick with some method of the Apache Edgent.

public class UltrasonicStream implements Supplier {

private static final long serialVersionUID = -6511218542753341056L;

private static GpioPinDigitalOutput sensorTriggerPin;
private static GpioPinDigitalInput sensorEchoPin;
private static final GpioController gpio = GpioFactory.getInstance();
private double currentDistance = -1.0;

/**
 * The HCSR04 Ultrasonic sensor is connected on the physical pin 16 and 18 which
 * correspond to the GPIO 04 and 05 of the WiringPi library.
 */
public UltrasonicStream() {
    // Trigger pin as OUTPUT
    sensorTriggerPin = gpio.provisionDigitalOutputPin(RaspiPin.GPIO_04);
    // Echo pin as INPUT
    sensorEchoPin = gpio.provisionDigitalInputPin(RaspiPin.GPIO_05, PinPullResistance.PULL_DOWN);
}

/**
 * This is the override method of the Supplier interface from Apache Edgent
 */
@Override
public Double get() {
    try {
        System.out.print("Distance in centimeters: ");
        currentDistance = getDistance();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return currentDistance;
}

/**
 * Retrieve the distance measured by the HCSR04 Ultrasonic sensor connected on a
 * Raspberry Pi 3+B
 * 
 * @return the distance in centimeters
 * @throws InterruptedException
 */
public double getDistance() throws InterruptedException {

    double distanceCM = -1;
    try {
        // Thread.sleep(2000);
        sensorTriggerPin.high(); // Make trigger pin HIGH
        Thread.sleep((long) 0.01);// Delay for 10 microseconds
        sensorTriggerPin.low(); // Make trigger pin LOW

        // Wait until the ECHO pin gets HIGH
        while (sensorEchoPin.isLow()) {

        }
        // Store the current time to calculate ECHO pin HIGH time.
        long startTime = System.nanoTime();
        // Wait until the ECHO pin gets LOW
        while (sensorEchoPin.isHigh()) {

        }
        // Store the echo pin HIGH end time to calculate ECHO pin HIGH time.
        long endTime = System.nanoTime();

        distanceCM = ((((endTime - startTime) / 1e3) / 2) / 29.1);
        // Printing out the distance in centimeters
        // System.out.println("Distance: " + distanceCM + " centimeters");

        return distanceCM;
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    return distanceCM;
}

}

Answer 1

I implemented like this:

UltrasonicStream sensor = new UltrasonicStream();

DirectProvider dp = new DirectProvider();

Topology topology = dp.newTopology();

TStream<Double> tempReadings = topology.poll(sensor, 3, TimeUnit.SECONDS);

TStream<Double> filteredReadings = tempReadings.filter(reading -> {
    boolean threshold = reading < 20 || reading > 80;
    if (!threshold) {
        System.out.println(String.format("Threshold reached: %s cm", reading));
    }
    return threshold;
});
filteredReadings.print();

dp.submit(topology);