net.derquinse.common.orm.hib.AbstractHibernateSequenceDAO.java Source code

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Here is the source code for net.derquinse.common.orm.hib.AbstractHibernateSequenceDAO.java

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/*
 * Copyright (C) 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 net.derquinse.common.orm.hib;

import java.lang.reflect.ParameterizedType;

import net.derquinse.common.orm.Sequence;
import net.derquinse.common.orm.SequenceDAO;
import net.derquinse.common.orm.SequenceNotFoundException;

import org.hibernate.LockOptions;
import org.hibernate.Session;
import org.hibernate.SessionFactory;

import com.google.common.base.Preconditions;

/**
 * Abstract DAO a sequence entity. WARNING: Transactional sequences are a source of locks and may
 * hurt scalability.
 * @author Andres Rodriguez
 * @param <T> Sequence type.
 */
public abstract class AbstractHibernateSequenceDAO<T extends Sequence> implements SequenceDAO {
    /** Persistent class. */
    private Class<T> persistentClass;
    /** Hibernate Session factory. */
    private final SessionFactory sessionFactory;

    /**
     * Initialized the DAO
     * @param sessionFactory Hibernate Session factory.
     */
    public AbstractHibernateSequenceDAO(final SessionFactory sessionFactory) {
        this.sessionFactory = Preconditions.checkNotNull(sessionFactory, "The session factory is mandatory.");
        @SuppressWarnings("unchecked")
        final Class<T> type = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass())
                .getActualTypeArguments()[0];
        this.persistentClass = type;
    }

    /**
     * Creates a new sequence.
     * @param id Sequence name.
     * @param initial Initial value.
     * @param increment Increment between values.
     * @return The newly created sequence.
     */
    protected abstract T create(String id, long initial, long increment);

    private static String nonNull(String id) {
        return Preconditions.checkNotNull(id, "The sequence name (id) is mandatory.");
    }

    /**
     * Gets the current value of a sequence.
     * @param id Sequence name.
     * @return The current value of the specified sequence.
     * @throws SequenceNotFoundException if the sequence is not found.
     */
    public long getCurrentValue(final String id) throws SequenceNotFoundException {
        nonNull(id);
        final Session session = sessionFactory.getCurrentSession();
        @SuppressWarnings("unchecked")
        final T sequence = (T) session.get(persistentClass, id, LockOptions.READ);
        if (sequence == null) {
            throw new SequenceNotFoundException(id);
        }
        return sequence.getCurrent();
    }

    /**
     * Gets the next value of a sequence. The row is locked in the current transaction.
     * @param id Sequence name.
     * @return The next value of the specified sequence.
     * @throws SequenceNotFoundException if the sequence is not found.
     */
    public long getNextValue(final String id) throws SequenceNotFoundException {
        nonNull(id);
        final Session session = sessionFactory.getCurrentSession();
        @SuppressWarnings("unchecked")
        final T sequence = (T) session.get(persistentClass, id, LockOptions.UPGRADE);
        if (sequence == null) {
            throw new SequenceNotFoundException(id);
        }
        final long next = sequence.getNext();
        session.update(sequence);
        return next;
    }

    /**
     * Gets the next value of a sequence, creating it if it does not exist.
     * @param id Sequence name.
     * @param initial Initial value.
     * @param increment Increment between values.
     * @return The next value of the specified sequence.
     */
    public long getNextValue(final String id, final long initial, final long increment) {
        nonNull(id);
        final Session session = sessionFactory.getCurrentSession();
        @SuppressWarnings("unchecked")
        T sequence = (T) session.get(persistentClass, id, LockOptions.UPGRADE);
        if (sequence != null) {
            return sequence.getNext();
        }
        // Create a new sequence and save it.
        sequence = create(id, initial, increment);
        session.save(sequence);
        // TODO: handle duplicates.
        return initial;
    }
}