FilterConditionComposite.java

/*
    BeepBeep, an event stream processor
    Copyright (C) 2008-2016 Sylvain Hall�

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package basic;

import static ca.uqac.lif.cep.Connector.INPUT;
import static ca.uqac.lif.cep.Connector.LEFT;
import static ca.uqac.lif.cep.Connector.OUTPUT;
import static ca.uqac.lif.cep.Connector.RIGHT;
import static ca.uqac.lif.cep.Connector.connect;
import ca.uqac.lif.cep.Pullable;
import ca.uqac.lif.cep.functions.StreamVariable;
import ca.uqac.lif.cep.functions.Constant;
import ca.uqac.lif.cep.functions.ApplyFunction;
import ca.uqac.lif.cep.functions.FunctionTree;
import ca.uqac.lif.cep.tmf.Filter;
import ca.uqac.lif.cep.tmf.Fork;
import ca.uqac.lif.cep.tmf.QueueSource;
import ca.uqac.lif.cep.util.Booleans;
import ca.uqac.lif.cep.util.Numbers;

/**
 * Filter a trace by evaluating a compound condition on the events of
 * that trace.
 * <p>
 * In this example, we wish to keep all events that are even <em>and</em>
 * greater than 4, and discard the others.
 * This example can be represented grahpically as:
 * <p>
 * <img src="./doc-files/basic/FilterConditionComposite.png" alt="Processor graph">
 * @author Sylvain Hallé
 * @difficulty Easy
 */
public class FilterConditionComposite
{
    public static void main(String[] args)
    {
        // Create a trace of dummy values
        QueueSource source_values = new QueueSource();
        source_values.setEvents(6, 5, 3, 8, 9, 2, 1, 7, 4, 5,
                2, 4, 7, 6, 12, 8, 1);
        // Fork the trace in two
        Fork fork = new Fork(2);
        connect(source_values, fork);
        // Connect the first ("left") output of the fork into a filter
        Filter filter = new Filter();
        connect(fork, LEFT, filter, LEFT);
        // Create the compound condition "is even and is greater than 4"
        FunctionTree tree = new FunctionTree(Booleans.and,
                Numbers.isEven,
                new FunctionTree(Numbers.isGreaterThan,
                        StreamVariable.X,
                        new Constant(4)));
        ApplyFunction condition = new ApplyFunction(tree);
        // Connect its input to the second output of the fork
        connect(fork, RIGHT, condition, INPUT);
        // Connect the condition as the second input of our filter
        connect(condition, OUTPUT, filter, RIGHT);
        // Get a reference to the filter's output pullable
        Pullable p = filter.getPullableOutput();
        // Pull 4 events from p
        for (int i = 0; i < 4; i++)
        {
            int x = (Integer) p.pull();
            System.out.printf("Output event #%d is %d\n", i, x);
        }
    }
}