ChecksumHelper


1   package fr.jayasoft.ivy.util;
2   
3   import java.io.BufferedReader  ;
4   import java.io.File  ;
5   import java.io.FileInputStream  ;
6   import java.io.FileReader  ;
7   import java.io.IOException  ;
8   import java.io.InputStream  ;
9   import java.security.MessageDigest  ;
10  import java.security.NoSuchAlgorithmException  ;
11  import java.util.HashMap  ;
12  import java.util.Map  ;
13  
14  public class ChecksumHelper {
15      
16      private static Map   _algorithms = new HashMap  ();
17      static {
18          _algorithms.put("md5", "MD5");
19          _algorithms.put("sha1", "SHA-1");
20      }
21      
22      public static boolean check(File   dest, File   checksumFile, String   algorithm) throws IOException   {
23          String   csFileContent = FileUtil.readEntirely(new BufferedReader  (new FileReader  (checksumFile))).trim().toLowerCase();
24          String   expected;
25          int spaceIndex = csFileContent.indexOf(' ');
26          if (spaceIndex != -1) {
27              expected = csFileContent.substring(0, spaceIndex);
28          } else {
29              expected = csFileContent;
30          }
31          
32          String   computed = computeAsString(dest, algorithm).trim().toLowerCase();
33          return expected.equals(computed);
34      }    
35      
36      public static String   computeAsString(File   f, String   algorithm) throws IOException   {
37          return byteArrayToHexString(compute(f, algorithm));
38      }
39      
40      private static byte[] compute(File   f, String   algorithm) throws IOException   {
41          InputStream   is = new FileInputStream  (f);
42  
43          try {
44              MessageDigest   md = getMessageDigest(algorithm);
45              md.reset();
46  
47              byte[] buf = new byte[2048];
48              int len = 0;
49              while ((len = is.read(buf)) != -1) {
50                  md.update(buf, 0, len);
51              }
52              return md.digest();
53          } finally {
54              is.close();
55          }
56      }
57  
58  
59      private static MessageDigest   getMessageDigest(String   algorithm) {
60          String   mdAlgorithm = (String  ) _algorithms.get(algorithm);
61          if (mdAlgorithm == null) {
62              throw new IllegalArgumentException  ("unknown algorithm "+algorithm);
63          }
64          try {
65              return MessageDigest.getInstance(mdAlgorithm);
66          } catch (NoSuchAlgorithmException   e) {
67              throw new IllegalArgumentException  ("unknown algorithm "+algorithm);
68          }
69      }
70  
71  
72      // byte to hex string converter
73      private final static char[] CHARS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
74      /**
75       * Convert a byte[] array to readable string format. This makes the "hex" readable!
76       * @return result String buffer in String format 
77       * @param in byte[] buffer to convert to string format
78       */
79      public static String   byteArrayToHexString(byte in[]) {
80          byte ch = 0x00;
81  
82          if (in == null || in.length <= 0) {
83              return null;
84          }
85  
86          StringBuffer   out = new StringBuffer  (in.length * 2);
87  
88          for (int i = 0; i < in.length; i++) {
89              ch = (byte) (in[i] & 0xF0); // Strip off high nibble
90              ch = (byte) (ch >>> 4); // shift the bits down
91              ch = (byte) (ch & 0x0F); // must do this is high order bit is on!
92  
93              out.append(CHARS[ (int) ch]); // convert the nibble to a String Character
94              ch = (byte) (in[i] & 0x0F); // Strip off low nibble 
95              out.append(CHARS[ (int) ch]); // convert the nibble to a String Character
96          }
97  
98          return out.toString();
99      }
100 
101 }
102
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