CacheEntry.java

/**
 * Copyright 2013 Flipkart Internet, pvt ltd.
 *
 * Licensed 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 lego.gracekelly.entities;

import lego.gracekelly.helpers.Ticker;

import java.io.Serializable;

/**
 * The CacheEntry class is a simple java object that holds data required to get, put and invalidate a cache entry.
 * The generic parameter indicates the type of the object that'll be store against the given key.
 * @param <T>
 */
public final class CacheEntry<T> implements Serializable {

    private final T value;
    private final String key;
    private final long ttl;
    private final long epoch_timestamp;

    public CacheEntry() {
        /*
        * Please refrain from using this constructor
        * This is meant for consumption by
        * serialization/de-serialization libraries
        * like Jackson
        * */
        ttl = 0;
        epoch_timestamp = 0;
        key = null;
        value = null;
    }

    /**
     * Constructor for an expirable CacheEntry
     * @param key
     * @param value
     * @param ttl
     */
    public CacheEntry(final String key, final T value, final long ttl){
        this.key = key;
        this.value = value;
        this.ttl = ttl;
        this.epoch_timestamp = Ticker.read();
    }

    /**
     * Constructor for a non-expirable CacheEntry
     * @param key
     * @param value
     */
    public CacheEntry(final String key, final T value){
        this.key = key;
        this.value = value;
        this.ttl = 0;
        this.epoch_timestamp = 0;
    }

    /**
     * Get's the value of the CacheEntry
     * @return value of the CacheEntry
     */
    public T getValue() {
        return value;
    }

    /**
     * Get's the key for the CacheEntry
     * @return key of the CacheEntry
     */
    public String getKey() {
        return key;
    }

    /**
     * Get's the ttl in seconds of the CacheEntry
     * @return ttl in seconds of the CacheEntry
     */
    public long getTtl() {
        return ttl;
    }

    /**
     * Get's the epoch_timestamp of when the CacheEntry was created this and ttl of the CacheEntry provide adequate
     * information to invalidate a CacheEntry.
     * @return the epoch timestamp of when this CacheEntry instance was created
     */
    public long getEpoch_timestamp() {
        return epoch_timestamp;
    }
}