org.guzz.id.TableHiLoGenerator.java Source code

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Here is the source code for org.guzz.id.TableHiLoGenerator.java

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/*
 * Copyright 2008-2009 the original author or authors.
 *
 * Licensed 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.guzz.id;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.guzz.GuzzContext;
import org.guzz.dialect.Dialect;
import org.guzz.orm.mapping.POJOBasedObjectMapping;
import org.guzz.transaction.TransactionManager;
import org.guzz.transaction.WriteTranSession;
import org.guzz.util.StringUtil;

/**
 * <b>hilo</b><br>
 * <br>
 * An <tt>IdentifierGenerator</tt> that returns a <tt>Long</tt>, constructed using
 * a hi/lo algorithm. The hi value MUST be fetched in a seperate transaction
 * to the <tt>Session</tt> transaction so the generator must be able to obtain
 * a new connection and commit it. Hence this implementation may not
 * be used  when the user is supplying connections. In this
 * case a <tt>SequenceHiLoGenerator</tt> would be a better choice (where
 * supported).<br>
 * <br>
 * Mapping parameters supported: table, column, db_group, max_lo
 *
 * @see SequenceHiLoGenerator
 */
public class TableHiLoGenerator extends TableGenerator {
    private static final Log log = LogFactory.getLog(TableHiLoGenerator.class);

    /**
     * The max_lo parameter
     */
    public static final String MAX_LO = "max_lo";

    private TransactionManager tm;

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

    public void configure(Dialect dialect, POJOBasedObjectMapping mapping, Properties params) {
        super.configure(dialect, mapping, params);

        this.maxLo = StringUtil.toInt(params.getProperty(MAX_LO), Short.MAX_VALUE);
        lo = maxLo + 1; // so we "clock over" on the first invocation
        this.returnType = pkColumn.getSqlDataType().getDataType();
    }

    public Serializable preInsert(WriteTranSession session, Object domainObject, Object tableCondition) {
        Serializable value = generate(tableCondition);

        setPrimaryKey(domainObject, value);

        return (Serializable) value;
    }

    public synchronized Number generate(Object tableCondition) {
        if (maxLo < 1) {
            //open a new transaction.
            WriteTranSession session = this.tm.openRWTran(true);

            try {
                //keep the behavior consistent even for boundary usages
                Integer n = super.nextValueInTable(session, tableCondition);

                if (n.intValue() == 0) {
                    n = super.nextValueInTable(session, tableCondition);
                }

                return IdentifierGeneratorFactory.createNumber(n.longValue(), this.returnType);
            } finally {
                session.close();
            }
        }

        if (lo > maxLo) {
            //open a new transaction.
            WriteTranSession session = this.tm.openRWTran(true);

            try {
                Number n = super.nextValueInTable(session, tableCondition);

                int hival = n.intValue();
                lo = (hival == 0) ? 1 : 0;
                hi = hival * (maxLo + 1);

                if (log.isDebugEnabled()) {
                    log.debug("new hi value: " + hival);
                }
            } finally {
                session.close();
            }
        }

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

    public void setGuzzContext(GuzzContext guzzContext) {
        this.tm = guzzContext.getTransactionManager();
    }

}