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1 package nl.hippo.uidgenerator;
2
3 import java.net.InetAddress  ;
4 import java.net.UnknownHostException ;
5 import java.security.SecureRandom ;
6
7
13 public class UIDGenerator
14 {
15 private SecureRandom m_randomNumberGenerator;
16
17 private String m_middle16Characters;
18
19 private static UIDGenerator s_instance;
20
21 public static String generateUID() throws UIDGeneratorException
22 {
23 return getInstance().generateNext();
24 }
25
26 public UIDGenerator() throws UIDGeneratorException
27 {
28 super();
29 m_randomNumberGenerator = new SecureRandom ();
30 StringBuffer middle16Characters = new StringBuffer ();
31 middle16Characters.append(toHexString(getLeastSignificantIpAddressData()));
32 middle16Characters.append(toHexString(System.identityHashCode(this)));
33 m_middle16Characters = middle16Characters.toString();
34 }
35
36 public String generateNext()
37 {
38 int first32Bits = (int) (System.currentTimeMillis() & 0xFFFFFFFFl);
39 int fourth32Bits = getNextRandomNumber();
40 StringBuffer result = new StringBuffer (toHexString(first32Bits));
41 result.append(m_middle16Characters);
42 result.append(toHexString(fourth32Bits));
43 return result.toString();
44 }
45
46 private static synchronized UIDGenerator getInstance() throws UIDGeneratorException
47 {
48 if (s_instance == null)
49 {
50 s_instance = new UIDGenerator();
51 }
52 return s_instance;
53 }
54
55 private static int getLeastSignificantIpAddressData() throws UIDGeneratorException
56 {
57 int result = 0;
58 try
59 {
60 byte[] ipAddress = InetAddress.getLocalHost().getAddress();
61 if (ipAddress.length >= 4)
62 {
63 for (int i = 0; i < 4; i++)
64 {
65 result <<= 8;
66 result += ipAddress[ipAddress.length - 4 + i] & 0xFF;
67 }
68 }
69 else
70 {
71 throw new UIDGeneratorException("Not enough information in IP address");
72 }
73 }
74 catch (UnknownHostException e)
75 {
76 throw new UIDGeneratorException(e);
77 }
78
79 return result;
80 }
81
82 private static String toHexString(int value)
83 {
84 String hexStringWithLeadingZeros = "0000000" + Integer.toHexString(value);
85 return hexStringWithLeadingZeros.substring(hexStringWithLeadingZeros.length() - 8);
86 }
87
88 private int getNextRandomNumber()
89 {
90 return m_randomNumberGenerator.nextInt();
91 }
92
93 }
94 |
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