A 32 byte GUID generator (Globally Unique ID). - Java java.util

Java examples for java.util:UUID

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Description

A 32 byte GUID generator (Globally Unique ID).

Demo Code


//package com.java2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        Object o = "java2s.com";
        System.out.println(generateGUID(o));
    }//from w  w  w . j  a  v  a 2s  . c  om

    /** Cached per JVM server IP. */
    private static String hexServerIP = null;
    private static final java.security.SecureRandom seeder = new java.security.SecureRandom();

    /**
     * A 32 byte GUID generator (Globally Unique ID). These artificial keys SHOULD <strong>NOT </strong> be seen by the user,
     * not even touched by the DBA but with very rare exceptions, just manipulated by the database and the programs.
     *
     * Usage: Add an id field (type java.lang.String) to your EJB, and add setId(XXXUtil.generateGUID(this)); to the ejbCreate method.
     */
    public static final String generateGUID(Object o) {
        StringBuffer tmpBuffer = new StringBuffer(16);
        if (hexServerIP == null) {
            java.net.InetAddress localInetAddress = null;
            try {
                // get the inet address

                localInetAddress = java.net.InetAddress.getLocalHost();
            } catch (java.net.UnknownHostException uhe) {
                System.err
                        .println("AccountUtil: Could not get the local IP address using InetAddress.getLocalHost()!");
                // todo: find better way to get around this...
                uhe.printStackTrace();
                return null;
            }
            byte serverIP[] = localInetAddress.getAddress();
            hexServerIP = hexFormat(getInt(serverIP), 8);
        }

        String hashcode = hexFormat(System.identityHashCode(o), 8);
        tmpBuffer.append(hexServerIP);
        tmpBuffer.append(hashcode);

        long timeNow = System.currentTimeMillis();
        int timeLow = (int) timeNow & 0xFFFFFFFF;
        int node = seeder.nextInt();

        StringBuffer guid = new StringBuffer(32);
        guid.append(hexFormat(timeLow, 8));
        guid.append(tmpBuffer.toString());
        guid.append(hexFormat(node, 8));
        return guid.toString();
    }

    private static String hexFormat(int i, int j) {
        String s = Integer.toHexString(i);
        return padHex(s, j) + s;
    }

    private static int getInt(byte bytes[]) {
        int i = 0;
        int j = 24;
        for (int k = 0; j >= 0; k++) {
            int l = bytes[k] & 0xff;
            i += l << j;
            j -= 8;
        }
        return i;
    }

    private static String padHex(String s, int i) {
        StringBuffer tmpBuffer = new StringBuffer();
        if (s.length() < i) {
            for (int j = 0; j < i - s.length(); j++) {
                tmpBuffer.append('0');
            }
        }
        return tmpBuffer.toString();
    }
}

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