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1   /*
2    * ====================================================================
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *   http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing,
14   * software distributed under the License is distributed on an
15   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16   * KIND, either express or implied.  See the License for the
17   * specific language governing permissions and limitations
18   * under the License.
19   * ====================================================================
20   *
21   * This software consists of voluntary contributions made by many
22   * individuals on behalf of the Apache Software Foundation.  For more
23   * information on the Apache Software Foundation, please see
24   * <http://www.apache.org/>.
25   *
26   */
27  package org.apache.http.client.cache;
28  
29  import java.io.IOException;
30  
31  /**
32   * Used for atomically updating entries in a {@link HttpCacheStorage}
33   * implementation. The current entry (if any) is fed into an implementation
34   * of this interface, and the new, possibly updated entry (if any)
35   * should be returned.
36   */
37  public interface HttpCacheUpdateCallback {
38  
39      /**
40       * Returns the new cache entry that should replace an existing one.
41       *
42       * @param existing
43       *            the cache entry currently in-place in the cache, possibly
44       *            {@code null} if nonexistent
45       * @return the cache entry that should replace it, again,
46       *         possibly {@code null} if the entry should be deleted
47       *
48       * @since 4.1
49       */
50      HttpCacheEntry update(HttpCacheEntry existing) throws IOException;
51  
52  }