HashvalueAlgorithm


1   /*
2    *  Licensed to the Apache Software Foundation (ASF) under one or more
3    *  contributor license agreements.  See the NOTICE file distributed with
4    *  this work for additional information regarding copyright ownership.
5    *  The ASF licenses this file to You under the Apache License, Version 2.0
6    *  (the "License"); you may not use this file except in compliance with
7    *  the License.  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  
19  package org.apache.tools.ant.types.selectors.modifiedselector;
20  
21  
22  import java.io.File  ;
23  
24  
25  /**
26   * Computes a 'hashvalue' for the content of file using String.hashValue().
27   * Use of this algorithm doesn't require any additional nested <param>s and
28   * doesn't support any.
29   *
30   * @version 2003-09-13
31   * @since  Ant 1.6
32   */
33  public class HashvalueAlgorithm implements Algorithm {
34  
35      /**
36       * This algorithm doesn't need any configuration.
37       * Therefore it's always valid.
38       * @return always true
39       */
40      public boolean isValid() {
41          return true;
42      }
43  
44      /**
45       * Computes a 'hashvalue' for a file content.
46       * It reads the content of a file, convert that to String and use the
47       * String.hashCode() method.
48       * @param file  The file for which the value should be computed
49       * @return the hashvalue or <i>null</i> if the file couldn't be read
50       */
51       // Because the content is only read the file will not be damaged. I tested
52       // with JPG, ZIP and PDF as binary files.
53      public String   getValue(File   file) {
54          try {
55              if (!file.canRead()) {
56                  return null;
57              }
58              java.io.FileInputStream   fis = new java.io.FileInputStream  (file);
59              byte[] content = new byte[fis.available()];
60              fis.read(content);
61              fis.close();
62              String   s = new String  (content);
63              int hash = s.hashCode();
64              return Integer.toString(hash);
65          } catch (Exception   e) {
66              return null;
67          }
68      }
69  
70  
71      /**
72       * Override Object.toString().
73       * @return information about this comparator
74       */
75      public String   toString() {
76          return "HashvalueAlgorithm";
77      }
78  
79  }
80
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