How JPA or Hibernate generate UUID as key? - mysql

Question

I am trying to use UUID as key with Mybatis. There are usually two ways:
Generate user keys in code.
Use uuid() method in mysql.
The first soluation should be a better choice for me, my question is how to implement a method to generate UUID as keys as JPA or Hibernate does? Their UUID keys is not a standard UUID.
with no dash.
rearrange the sequence for better performance.

Answer 1

I used｀UUIDHexGenerator｀ from Hibernate to generate UUID now.
UUIDHexGenerator.java
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
* indicated by the #author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Middleware LLC.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*
*/
import java.io.Serializable;
/**
* <b>uuid</b><br>
* <br>
* A <tt>UUIDGenerator</tt> that returns a string of length 32,
* This string will consist of only hex digits. Optionally,
* the string may be generated with separators between each
* component of the UUID.
*
* Mapping parameters supported: separator.
*
* #author Gavin King
*/
public class UUIDHexGenerator extends AbstractUUIDGenerator {
private String sep = "";
protected String format(int intval) {
String formatted = Integer.toHexString(intval);
StringBuffer buf = new StringBuffer("00000000");
buf.replace( 8-formatted.length(), 8, formatted );
return buf.toString();
}
protected String format(short shortval) {
String formatted = Integer.toHexString(shortval);
StringBuffer buf = new StringBuffer("0000");
buf.replace( 4-formatted.length(), 4, formatted );
return buf.toString();
}
public Serializable generate() {
return new StringBuffer(36)
.append( format( getIP() ) ).append(sep)
.append( format( getJVM() ) ).append(sep)
.append( format( getHiTime() ) ).append(sep)
.append( format( getLoTime() ) ).append(sep)
.append( format( getCount() ) )
.toString();
}
public static void main( String[] args ) throws Exception {
UUIDHexGenerator gen = new UUIDHexGenerator();
UUIDHexGenerator gen2 = new UUIDHexGenerator();
for ( int i=0; i<100; i++) {
String id = (String) gen.generate();
System.out.println(id);
String id2 = (String) gen2.generate();
System.out.println(id2);
String id3 = (String) gen2.generate();
System.out.println(id3);
}
}
}
BytesHelper.java
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
* indicated by the #author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Middleware LLC.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*
*/
public final class BytesHelper {
private BytesHelper() {}
public static int toInt( byte[] bytes ) {
int result = 0;
for (int i=0; i<4; i++) {
result = ( result << 8 ) - Byte.MIN_VALUE + (int) bytes[i];
}
return result;
}
}
AbstractUUIDGenerator.java
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
* indicated by the #author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Middleware LLC.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*
*/
import java.net.InetAddress;
/**
* The base class for identifier generators that use a UUID algorithm. This
* class implements the algorithm, subclasses define the identifier
* format.
*
* #see UUIDHexGenerator
* #author Gavin King
*/
public abstract class AbstractUUIDGenerator {
private static final int IP;
static {
int ipadd;
try {
ipadd = BytesHelper.toInt( InetAddress.getLocalHost().getAddress() );
}
catch (Exception e) {
ipadd = 0;
}
IP = ipadd;
}
private static short counter = (short) 0;
private static final int JVM = (int) ( System.currentTimeMillis() >>> 8 );
public AbstractUUIDGenerator() {
}
/**
* Unique across JVMs on this machine (unless they load this class
* in the same quater second - very unlikely)
*/
protected int getJVM() {
return JVM;
}
/**
* Unique in a millisecond for this JVM instance (unless there
* are > Short.MAX_VALUE instances created in a millisecond)
*/
protected short getCount() {
synchronized(AbstractUUIDGenerator.class) {
if (counter<0) counter=0;
return counter++;
}
}
/**
* Unique in a local network
*/
protected int getIP() {
return IP;
}
/**
* Unique down to millisecond
*/
protected short getHiTime() {
return (short) ( System.currentTimeMillis() >>> 32 );
}
protected int getLoTime() {
return (int) System.currentTimeMillis();
}
}