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 /*
  * Copyright 2010 Amazon.com, Inc. or its affiliates. All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (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/apache2.0
  *
 * 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.util;
Cache of response metadata for recently executed requests for diagnostic purposes. This cache has a max size and as entries are added, the oldest entry is aged out once the max size has been reached.
public class ResponseMetadataCache {
    private final int maxEntries;
    private Map<IntegerResponseMetadatamap;
    private List<ObjectobjectList;

    
Creates a new cache that will contain, at most the specified number of entries.

Parameters:
maxEntries The maximum size of this cache.
    public ResponseMetadataCache(int maxEntries) {
        this. = maxEntries;
         = new ArrayList<Object>(maxEntries);
         = new HashMap<IntegerResponseMetadata>();
    }

    
Adds a new entry to this cache, possibly evicting the oldest entry if the cache is at its size limit.

Parameters:
obj The key by which to store the metadata.
metadata The metadata for this entry.
    public synchronized void add(Object objResponseMetadata metadata) {
        if (obj == nullreturn;
        if (.size() >= evictOldest();
        store(System.identityHashCode(obj), metadata);
    }

    
Returns the response metadata associated with the specified object, or null if no metadata is associated with that object.

Parameters:
obj The key by which the desired metadata is stored.
Returns:
The response metadata associated with the given object key, otherwise null if no metadata is associated with that object.
    public ResponseMetadata get(Object obj) {
        // System.identityHashCode isn't guaranteed to be unique
        // on all platforms, but should be reasonable enough to use
        // for a few requests at a time.  We can always easily move
        // to our own unique IDs if needed.
        return .get(System.identityHashCode(obj));
    }
    private void evictOldest() {
        .remove(.remove(0));
    }
    private void store(int idResponseMetadata metadata) {
        .put(idmetadata);
        .add(id);
    }
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