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1
56 package org.objectstyle.cayenne.util;
57
58 import java.net.UnknownHostException  ;
59 import java.security.MessageDigest ;
60 import java.security.NoSuchAlgorithmException ;
61
62 import org.objectstyle.cayenne.CayenneRuntimeException;
63
64
69 public class IDUtil {
70
71 private static volatile long currentId = Long.MIN_VALUE;
72 private static MessageDigest md;
73 private static byte[] ipAddress;
74
75 static {
76 try {
77 md = MessageDigest.getInstance("MD5");
78 } catch (NoSuchAlgorithmException e) {
79 throw new CayenneRuntimeException("Can't initialize MessageDigest.", e);
80 }
81
82 try {
83 ipAddress = java.net.InetAddress.getLocalHost().getAddress();
84 } catch (UnknownHostException e) {
85 ipAddress = new byte[] { 127, 0, 0, 1 };
87 }
88 }
89
90
98 public synchronized static byte[] pseudoUniqueByteSequence(int length) {
99 if (length < 16) {
100 throw new IllegalArgumentException (
101 "Can't generate unique byte sequence shorter than 16 bytes: " + length);
102 }
103
104 if (length == 16) {
105 return pseudoUniqueByteSequence16();
106 }
107
108 byte[] bytes = new byte[length];
109 for (int i = 0; i <= length - 16; i += 16) {
110 byte[] nextSequence = pseudoUniqueByteSequence16();
111 System.arraycopy(nextSequence, 0, bytes, i, 16);
112 }
113
114 int leftoverLen = length % 16;
116 if (leftoverLen > 0) {
117 byte[] nextSequence = pseudoUniqueByteSequence16();
118 System.arraycopy(nextSequence, 0, bytes, length - leftoverLen, leftoverLen);
119 }
120
121 return bytes;
122 }
123
124
127 public static byte[] pseudoUniqueByteSequence16() {
128 byte[] bytes = new byte[20];
129
130 appendLongBytes(bytes, 0, System.currentTimeMillis());
131 appendLongBytes(bytes, 8, currentId++);
132 System.arraycopy(ipAddress, 0, bytes, 16, ipAddress.length);
133
134 try {
136 Thread.sleep(2);
137 } catch (InterruptedException e) {
138 }
140
141 return md.digest(bytes);
142 }
143
144
145 private static void appendLongBytes(byte[] bytes, int offset, long value) {
146 for (int i = 0; i < 8; ++i) {
147 int off = (7 - i) * 8;
148 bytes[i + offset] = (byte) ((value & (0xff << off)) >>> off);
149 }
150 }
151
152 private IDUtil() {
153 }
154
155 }
156 |
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