com.amazonaws.services.dynamodbv2.streamsadapter.AdapterRequestCache Maven / Gradle / Ivy

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/*
 * Copyright 2014-2015 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Amazon Software License (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 * http://aws.amazon.com/asl/
 *
 * or in the "license" file accompanying this file. This file 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.amazonaws.services.dynamodbv2.streamsadapter;

import java.util.Deque;
import java.util.HashMap;
import java.util.LinkedList;

import com.amazonaws.AmazonWebServiceRequest;

/**
 * Cache for mapping Kinesis requests to DynamoDB Streams requests. Evicts oldest cache entry if adding a new entry exceeds the cache capacity.
 */
public class AdapterRequestCache {
    /**
     * Map for request lookup.
     */
    private final HashMap cacheMap = new HashMap();
    /**
     * Deque for evicting old cache entries.
     */
    private final Deque evictQueue = new LinkedList();
    /**
     * Capacity for the cache.
     */
    private final int capacity;

    public AdapterRequestCache(int capacity) {
        if (capacity <= 0) {
            throw new IllegalArgumentException("Capacity must be a positive number");
        }
        this.capacity = capacity;
    }

    /**
     * Adds an entry to the cache.
     *
     * @param request
     *            Kinesis request
     * @param requestAdapter
     *            DynamoDB adapter client wrapper for the Kinesis request
     */
    public synchronized void addEntry(AmazonWebServiceRequest request, AmazonWebServiceRequest requestAdapter) {
        if (null == request || null == requestAdapter) {
            throw new IllegalArgumentException("Request and adapter request must not be null");
        }
        if (evictQueue.size() == capacity) {
            Integer evicted = evictQueue.removeLast();
            cacheMap.remove(evicted);
        }
        evictQueue.addFirst(System.identityHashCode(request));
        cacheMap.put(System.identityHashCode(request), requestAdapter);
    }

    /**
     * Gets the actual DynamoDB Streams request made for a Kinesis request.
     *
     * @param request
     *            Kinesis request
     * @return actual DynamoDB Streams request made for the associated Kinesis request
     */
    public synchronized AmazonWebServiceRequest getEntry(AmazonWebServiceRequest request) {
        if (null == request) {
            throw new IllegalArgumentException("Request must not be null");
        }
        return cacheMap.get(System.identityHashCode(request));
    }

}