mitm.common.hibernate.AbstractScrollableResultsIterator.java Source code

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Here is the source code for mitm.common.hibernate.AbstractScrollableResultsIterator.java

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/*
 * Copyright (c) 2008-2011, Martijn Brinkers, Djigzo.
 * 
 * This file is part of Djigzo email encryption.
 *
 * Djigzo is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License 
 * version 3, 19 November 2007 as published by the Free Software 
 * Foundation.
 *
 * Djigzo 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public 
 * License along with Djigzo. If not, see <http://www.gnu.org/licenses/>
 *
 * Additional permission under GNU AGPL version 3 section 7
 * 
 * If you modify this Program, or any covered work, by linking or 
 * combining it with aspectjrt.jar, aspectjweaver.jar, tyrex-1.0.3.jar, 
 * freemarker.jar, dom4j.jar, mx4j-jmx.jar, mx4j-tools.jar, 
 * spice-classman-1.0.jar, spice-loggerstore-0.5.jar, spice-salt-0.8.jar, 
 * spice-xmlpolicy-1.0.jar, saaj-api-1.3.jar, saaj-impl-1.3.jar, 
 * wsdl4j-1.6.1.jar (or modified versions of these libraries), 
 * containing parts covered by the terms of Eclipse Public License, 
 * tyrex license, freemarker license, dom4j license, mx4j license,
 * Spice Software License, Common Development and Distribution License
 * (CDDL), Common Public License (CPL) the licensors of this Program grant 
 * you additional permission to convey the resulting work.
 */
package mitm.common.hibernate;

import java.lang.reflect.ParameterizedType;

import mitm.common.reflection.ReflectionUtils;
import mitm.common.util.Check;
import mitm.common.util.CloseableIterator;
import mitm.common.util.CloseableIteratorException;

import org.apache.commons.lang.IllegalClassException;
import org.hibernate.ScrollableResults;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * {@link CloseableIterator} implementation that can be used as a base class to iterate over entries in
 * a database using a {@link ScrollableResults} as the data source.
 * 
 * @author Martijn Brinkers
 *
 * @param <T>
 */
public abstract class AbstractScrollableResultsIterator<T> implements CloseableIterator<T> {
    private final static Logger logger = LoggerFactory.getLogger(AbstractScrollableResultsIterator.class);

    private final Class<T> persistentClass;

    private final ScrollableResults results;

    private T nextElement;
    private boolean closed;

    @SuppressWarnings("unchecked")
    public AbstractScrollableResultsIterator(ScrollableResults results) {
        Check.notNull(results, "results");

        this.results = results;

        this.persistentClass = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass())
                .getActualTypeArguments()[0];
    }

    protected Object parseElement(Object element) {
        if (!ReflectionUtils.isInstanceOf(element.getClass(), persistentClass)) {
            throw new IllegalClassException("The object returned from the ScrollableResults is not a "
                    + persistentClass.getCanonicalName());
        }

        return element;
    }

    abstract protected boolean hasMatch(T element);

    protected Object get(ScrollableResults results) {
        return results.get(0);
    }

    @Override
    @SuppressWarnings("unchecked")
    public boolean hasNext() throws CloseableIteratorException {
        if (closed) {
            throw new CloseableIteratorException("This iterator is closed.");
        }

        if (nextElement != null) {
            return true;
        }

        T newElement = null;

        boolean hasNext = false;

        while (results.next()) {
            Object object = get(results);

            object = parseElement(object);

            newElement = (T) object;

            if (!hasMatch(newElement)) {
                continue;
            }

            hasNext = true;
            break;
        }

        if (hasNext) {
            nextElement = newElement;
        } else {
            /* close if we have arrived at the last entry */
            close();
        }

        return hasNext;
    }

    @Override
    public T next() throws CloseableIteratorException {
        if (closed) {
            throw new CloseableIteratorException("This iterator is closed.");
        }

        if (nextElement == null) {
            if (!hasNext()) {
                throw new CloseableIteratorException("There is not next entry.");
            }
        }

        T copy = nextElement;

        nextElement = null;

        return copy;
    }

    @Override
    public void close() throws CloseableIteratorException {
        logger.debug("Closing iterator.");

        if (!closed) {
            results.close();

            closed = true;
        }
    }

    @Override
    public boolean isClosed() throws CloseableIteratorException {
        return closed;
    }
}