CountTrigger.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.alibaba.jstorm.window;

/**
 * A {@link Trigger} that fires once the count of elements in a pane reaches the given count.
 */
public class CountTrigger<T> extends Trigger<T> {
    private static final long serialVersionUID = 1L;

    private final long maxCount;
    private long count;

    private CountTrigger(long maxCount) {
        this.maxCount = maxCount;
    }

    @Override
    public TriggerResult onElement(Object element, long timestamp, TimeWindow window, TriggerContext ctx) {
        count++;
        if (count >= maxCount) {
            count = 0;
            return TriggerResult.FIRE;
        }
        return TriggerResult.CONTINUE;
    }

    @Override
    public String toString() {
        return "CountTrigger(" + maxCount + ")";
    }

    /**
     * Creates a trigger that fires once the number of elements in a pane reaches the given count.
     *
     * @param maxCount The count of elements at which to fire.
     */
    public static <T> CountTrigger<T> of(long maxCount) {
        return new CountTrigger<>(maxCount);
    }
}