samples/topology/src/main/java/org/apache/edgent/samples/topology/PeriodicSource.java

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to you under the Apache License, Version 2.0 (the
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  http://www.apache.org/licenses/LICENSE-2.0

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package org.apache.edgent.samples.topology;

import java.util.Random;
import java.util.concurrent.TimeUnit;

import org.apache.edgent.providers.direct.DirectProvider;
import org.apache.edgent.topology.TStream;
import org.apache.edgent.topology.Topology;

/**
 * Periodic polling of source data.
 *
 */
public class PeriodicSource {
    /**
     * Shows polling a data source to periodically obtain a value.
     * Polls a random number generator for a new value every second
     * and then prints out the raw value and a filtered and transformed stream.
     * @param args command arguments
     * @throws Exception on failure
     */
    public static void main(String[] args) throws Exception {

        DirectProvider tp = new DirectProvider();

        Topology t = tp.newTopology("PeriodicSource");

        // Since this is the Direct provider the graph can access
        // objects created while the topology is being defined
        // (in this case the Random object r).
        Random r = new Random();
        TStream<Double> gaussian = t.poll(() -> r.nextGaussian(), 1, TimeUnit.SECONDS);

        // Peek at the value on the Stream printing it to System.out
        gaussian = gaussian.peek(g -> System.out.println("R:" + g));

        // A filter
        gaussian = gaussian.filter(g -> g > 0.5);

        // A transformation
        TStream<String> gs = gaussian.map(g -> "G:" + g + ":");
        gs.print();

        tp.submit(t);
    }
}