com.alibaba.metrics.DerivativeGauge Maven / Gradle / Ivy

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/*
 * 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.metrics;

/**
 * A gauge whose value is derived from the value of another gauge.
 *
 * @param  the base gauge's value type
 * @param  the derivative type
 */
public abstract class DerivativeGauge implements Gauge {

    private final Gauge base;
    private long lastUpdate;

    /**
     * Creates a new derivative with the given base gauge.
     *
     * @param base the gauge from which to derive this gauge's value
     */
    protected DerivativeGauge(Gauge base) {
        this.base = base;
    }

    @Override
    public T getValue() {
        T result = transform(base.getValue());
        lastUpdate = System.currentTimeMillis();
        return result;
    }

    @Override
    public long lastUpdateTime() {
        return lastUpdate;
    }

    /**
     * Transforms the value of the base gauge to the value of this gauge.
     *
     * @param value the value of the base gauge
     * @return this gauge's value
     */
    protected abstract T transform(F value);
}