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1   /*** 
2    * 
3    * Copyright 2004 Protique Ltd
4    * 
5    * Licensed under the Apache License, Version 2.0 (the "License"); 
6    * you may not use this file except in compliance with the License. 
7    * You may obtain a copy of the License at 
8    * 
9    * http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS, 
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
14   * See the License for the specific language governing permissions and 
15   * limitations under the License. 
16   * 
17   **/
18  package org.codehaus.activemq.util;
19  
20  import org.apache.commons.logging.Log;
21  import org.apache.commons.logging.LogFactory;
22  
23  import java.net.InetAddress;
24  import java.net.ServerSocket;
25  
26  /***
27   * Generator for globally unique Strings
28   *
29   * @version $Revision: 1.1 $
30   */
31  public class IdGenerator {
32      private static final Log log = LogFactory.getLog(IdGenerator.class);
33      private static final String UNIQUE_STUB;
34      private static int instanceCount;
35      private static String hostName;
36      private String seed;
37      private long sequence;
38  
39      static {
40          String stub = "";
41          boolean canAccessSystemProps = true;
42          try {
43              SecurityManager sm = System.getSecurityManager();
44              if (sm != null) {
45                  sm.checkPropertiesAccess();
46              }
47          }
48          catch (SecurityException se) {
49              canAccessSystemProps = false;
50          }
51          if (canAccessSystemProps) {
52              try {
53                  hostName = InetAddress.getLocalHost().getHostName();
54                  ServerSocket ss = new ServerSocket(0);
55                  stub = "ID:" + hostName + "-" + ss.getLocalPort() + "-" + System.currentTimeMillis() + "-";
56                  Thread.sleep(100);
57                  ss.close();
58              }
59              catch (Exception ioe) {
60                  log.warn("could not generate unique stub", ioe);
61              }
62          }
63          else {
64              hostName = "localhost";
65              stub = "ID:" + hostName + "-1-" + System.currentTimeMillis() + "-";
66          }
67          UNIQUE_STUB = stub;
68      }
69  
70      /***
71       * As we have to find the hostname as a side-affect of generating a unique stub, we allow it's easy retrevial here
72       *
73       * @return the local host name
74       */
75      public static String getHostName() {
76          return hostName;
77      }
78  
79      /***
80       * Construct an IdGenerator
81       */
82      public IdGenerator() {
83          synchronized (UNIQUE_STUB) {
84              this.seed = UNIQUE_STUB + (instanceCount++) + ":";
85          }
86      }
87  
88      /***
89       * Generate a unqiue id
90       *
91       * @return a unique id
92       */
93      public synchronized String generateId() {
94          return this.seed + (this.sequence++);
95      }
96  
97      /***
98       * @return the unique seed used by this generator
99       */
100     public String getSeed() {
101         return seed;
102     }
103 
104     /***
105      * From a generated id - return the seed (i.e. minus the count)
106      *
107      * @param id the generated identifer
108      * @return
109      */
110     public static String getSeedFromId(String id) {
111         String result = id;
112         if (id != null) {
113             int index = id.lastIndexOf(':');
114             if (index > 0 && (index + 1) < id.length()) {
115                 result = id.substring(0, index + 1);
116             }
117         }
118         return result;
119     }
120 
121     /***
122      * From a generated id - return the generator count
123      *
124      * @param id
125      * @return the count
126      */
127     public static long getCountFromId(String id) {
128         long result = -1;
129         if (id != null) {
130             int index = id.lastIndexOf(':');
131 
132             if (index > 0 && (index + 1) < id.length()) {
133                 String numStr = id.substring(index + 1, id.length());
134                 result = Long.parseLong(numStr);
135             }
136         }
137         return result;
138     }
139 
140     /***
141      * Does a proper compare on the ids
142      *
143      * @param id1
144      * @param id2
145      * @return
146      */
147 
148     public static int compare(String id1, String id2) {
149         int result = -1;
150         String seed1 = IdGenerator.getSeedFromId(id1);
151         String seed2 = IdGenerator.getSeedFromId(id2);
152         if (seed1 != null && seed2 != null) {
153             result = seed1.compareTo(seed2);
154             if (result == 0) {
155                 long count1 = IdGenerator.getCountFromId(id1);
156                 long count2 = IdGenerator.getCountFromId(id2);
157                 result = (int) (count1 - count2);
158             }
159         }
160         return result;
161 
162     }
163 }