Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied. See the License for the * specific language governing permissions and limitations * under the License. */ package org.wso2.carbon.humantask.core.utils; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import java.math.BigInteger; /** * This class is used to generate globally unique IDs. The requirements for * global uniqueness are as follows: * <p/> * <pre> * 1) The time on any machine is never set back. * 2) Each machine has a unique IP address. * 3) Each process has the 'org.apache.ode.uid.port' property set to the * same non-zero value. * * byte: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 * [ IPADDRESS ] [ START TIME IN MS ] [ count] * This format allow more compact string representation. * Persistence mechanism maps 6 bits to a number-char mapping. Byte * 0-5 (48 bits, 6 bits per char => 8 chars) * Since the current time typically has zeros for many of its most significant * digits, all leading zeros are truncated from the string representation. * The following 6 bit to char mapping is used: * 0-9 -> 0-9 * 10-35 -> A-Z * 36-60 -> a-y * 61 -> za * 62 -> zb * 63 -> zc * </pre> */ public final class GUID implements Cloneable, Comparable, java.io.Serializable { private static final Log log = LogFactory.getLog(GUID.class); static final long serialVersionUID = -7977671257884186039L; private static String propertyPort = "org.wso2.carbon.humantask.uid.port"; private static int port = Integer.getInteger(propertyPort, 33666); // 32 bits private static final byte[] ipadd = { 127, 0, 0, 1 }; // 64 bits private static byte[] baseId = getSystemUniqId(); // 32 bits private static short cnt = Short.MIN_VALUE; // private static GUID vmGuid; // // static { // vmGuid = new GUID(); // } private final byte[] id; private transient String guidstring = null; /** * Create a new unique GUID */ public GUID() { short c; byte[] b; synchronized (GUID.class) { c = ++cnt; b = baseId; if (cnt == Short.MAX_VALUE) { cnt = Short.MIN_VALUE; baseId = getSystemUniqId(); } } id = new byte[] { ipadd[0], ipadd[1], ipadd[2], ipadd[3], b[7], b[6], b[5], b[4], b[3], b[2], b[1], b[0], (byte) ((c >>> 8) & 0xff), (byte) (c & 0xff) }; } // /** // * Reconstitute a GUID from it's string representation // * // * @param str DOCUMENTME // * @throws MalformedGuidException DOCUMENTME // */ // public GUID(String str) throws MalformedGuidException { // if (str == null) { // throw new MalformedGuidException("String is null"); // } // // id = new byte[14]; // stringToBytes(str); // } // /** // * Get the GUID bytes. // * // * @return byte[] // */ // public byte[] getGuid() { // return id.clone(); // } // // public static GUID getVMGUID() { // return vmGuid; // } public int compareTo(Object o) { if (o == this) { return 0; } GUID o1 = (GUID) o; for (short i = 0; i < id.length; ++i) { if (o1.id[i] < id[i]) { return -1; } else if (o1.id[i] > id[i]) { return 1; } } return 0; } public boolean equals(Object o) { return o instanceof GUID && compareTo(o) == 0; } public int hashCode() { int ret = 0; for (short i = 0; i < id.length; ++i) { ret ^= (id[i] << (i % 4)); } return ret; } /** * Convert a GUID to it's string representation. This will return a string * of at most 32 bytes. * * @return DOCUMENTME */ public String toString() { if (guidstring == null) { guidstring = mapBytesToChars(); } return guidstring; } private static byte[] getSystemUniqId() { ProcessMutex pm = new ProcessMutex(port); try { pm.lock(); } catch (InterruptedException ie) { log.error("ERROR: Could not establish unique starttime using\n" + " TCP port " + port + " for synchronization. \n" + " Perhaps this port is used by anotherprocess? \n" + " Check the '" + propertyPort + "' JAVA system property. \n", ie); throw new RuntimeException("GUID.getSystemUniqId() FAILED!!!", ie); } long uid = System.currentTimeMillis(); pm.unlock(); return new byte[] { (byte) (uid & 0xff), (byte) ((uid >>> 8) & 0xff), (byte) ((uid >>> 16) & 0xff), (byte) ((uid >>> 24) & 0xff), (byte) ((uid >>> 32) & 0xff), (byte) ((uid >>> 40) & 0xff), (byte) ((uid >>> 48) & 0xff), (byte) ((uid >>> 56) & 0xff) }; } private String mapBytesToChars() { BigInteger bigInt = new BigInteger(id); return bigInt.toString(34); } // private void stringToBytes(String s) { // BigInteger bigInt = new BigInteger(s, 34); // byte[] bytes = bigInt.toByteArray(); // System.arraycopy(bytes, 0, id, 0, id.length); // } // // public static class MalformedGuidException extends Exception { // // private static final long serialVersionUID = -8922336058603571809L; // // public MalformedGuidException(String guid) { // super("Malformed guid: " + guid); // } // } // public static String makeGUID(String digest) { // String val = "0"; // int maxlen = 32; // int base = 34; // int prime = 31; // for (int i = 0; i < digest.length(); i++) { // char c = digest.charAt(i); // val = new BigInteger(val, base).add(BigInteger.valueOf((long) c)). // multiply(BigInteger.valueOf(prime)).toString(base); // if (val.length() > maxlen) { // val = val.substring(0, maxlen); // } // } // // return val; // } }