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1   /**
2    *  Copyright 2003-2006 Greg Luck
3    *
4    *  Licensed under the Apache License, Version 2.0 (the "License");
5    *  you may not use this file except in compliance with the License.
6    *  You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   *  Unless required by applicable law or agreed to in writing, software
11   *  distributed under the License is distributed on an "AS IS" BASIS,
12   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   *  See the License for the specific language governing permissions and
14   *  limitations under the License.
15   */
16  
17  package net.sf.ehcache.store;
18  
19  import org.apache.commons.logging.Log;
20  import org.apache.commons.logging.LogFactory;
21  
22  /**
23   * A typesafe enumeration of eviction policies.
24   * The policy used to evict elements from the {@link net.sf.ehcache.store.MemoryStore}.
25   * This can be one of:
26   * <ol>
27   * <li>LRU - least recently used
28   * <li>LFU - least frequently used
29   * <li>FIFO - first in first out, the oldest element by creation time
30   * </ol>
31   * The default value is LRU
32   *
33   * @author <a href="mailto:gluck@thoughtworks.com">Greg Luck</a>
34   * @version $Id: MemoryStoreEvictionPolicy.java 52 2006-04-24 14:50:03Z gregluck $
35   * @since 1.2
36   */
37  public final class MemoryStoreEvictionPolicy {
38  
39      /**
40       * LRU - least recently used.
41       */
42      public static final MemoryStoreEvictionPolicy LRU = new MemoryStoreEvictionPolicy("LRU");
43  
44      /**
45       * LFU - least frequently used.
46       */
47  
48      public static final MemoryStoreEvictionPolicy LFU = new MemoryStoreEvictionPolicy("LFU");
49  
50      /**
51       * FIFO - first in first out, the oldest element by creation time.
52       */
53      public static final MemoryStoreEvictionPolicy FIFO = new MemoryStoreEvictionPolicy("FIFO");
54  
55      private static final Log LOG = LogFactory.getLog(MemoryStoreEvictionPolicy.class.getName());
56  
57      // for debug only
58      private final String myName;
59  
60      /**
61       * This class should not be subclassed or have instances created.
62       * @param policy
63       */
64      private MemoryStoreEvictionPolicy(String policy) {
65          myName = policy;
66      }
67  
68      /**
69       * @return a String representation of the policy
70       */
71      public String toString() {
72          return myName;
73      }
74  
75      /**
76       * Converts a string representation of the policy into a policy.
77       *
78       * @param policy either LRU, LFU or FIFO
79       * @return one of the static instances
80       */
81      public static MemoryStoreEvictionPolicy fromString(String policy) {
82          if (policy != null) {
83              if (policy.equalsIgnoreCase("LRU")) {
84                  return LRU;
85              } else if (policy.equalsIgnoreCase("LFU")) {
86                  return LFU;
87              } else if (policy.equalsIgnoreCase("FIFO")) {
88                  return FIFO;
89              }
90          }
91  
92          if (LOG.isWarnEnabled()) {
93              LOG.warn("The memoryStoreEvictionPolicy of " + policy + " cannot be resolved. The policy will be" +
94                      " set to LRU");
95          }
96          return LRU;
97      }
98  }