sequencehilogenerator.java

一个Java持久层类库

//$Id: SequenceHiLoGenerator.java 9720 2006-03-31 00:11:54Z epbernard $
package org.hibernate.id;

import java.io.Serializable;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.hibernate.HibernateException;
import org.hibernate.MappingException;
import org.hibernate.dialect.Dialect;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.type.Type;
import org.hibernate.util.PropertiesHelper;

/**
 * <b>seqhilo</b><br>
 * <br>
 * An <tt>IdentifierGenerator</tt> that combines a hi/lo algorithm with an underlying
 * oracle-style sequence that generates hi values. The user may specify a
 * maximum lo value to determine how often new hi values are fetched.<br>
 * <br>
 * If sequences are not available, <tt>TableHiLoGenerator</tt> might be an
 * alternative.<br>
 * <br>
 * Mapping parameters supported: sequence, max_lo, parameters.
 *
 * @see TableHiLoGenerator
 * @author Gavin King
 */
public class SequenceHiLoGenerator extends SequenceGenerator {

	public static final String MAX_LO = "max_lo";

	private static final Logger log = LoggerFactory.getLogger(SequenceHiLoGenerator.class);

	private int maxLo;
	private int lo;
	private long hi;
	private Class returnClass;

	public void configure(Type type, Properties params, Dialect d) throws MappingException {
		super.configure(type, params, d);
		maxLo = PropertiesHelper.getInt(MAX_LO, params, 9);
		lo = maxLo + 1; // so we "clock over" on the first invocation
		returnClass = type.getReturnedClass();
	}

	public synchronized Serializable generate(SessionImplementor session, Object obj) 
	throws HibernateException {
		if (maxLo < 1) {
			//keep the behavior consistent even for boundary usages
			long val = ( (Number) super.generate(session, obj) ).longValue();
			if (val == 0) val = ( (Number) super.generate(session, obj) ).longValue();
			return IdentifierGeneratorFactory.createNumber( val, returnClass );
		}
		if ( lo>maxLo ) {
			long hival = ( (Number) super.generate(session, obj) ).longValue();
			lo = (hival == 0) ? 1 : 0;
			hi = hival * ( maxLo+1 );
			if ( log.isDebugEnabled() )
				log.debug("new hi value: " + hival);
		}

		return IdentifierGeneratorFactory.createNumber( hi + lo++, returnClass );
	}

}