001    /*
002     * JBoss, Home of Professional Open Source.
003     * Copyright 2008, Red Hat Middleware LLC, and individual contributors
004     * as indicated by the @author tags. See the copyright.txt file in the
005     * distribution for a full listing of individual contributors.
006     *
007     * This is free software; you can redistribute it and/or modify it
008     * under the terms of the GNU Lesser General Public License as
009     * published by the Free Software Foundation; either version 2.1 of
010     * the License, or (at your option) any later version.
011     *
012     * This software is distributed in the hope that it will be useful,
013     * but WITHOUT ANY WARRANTY; without even the implied warranty of
014     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
015     * Lesser General Public License for more details.
016     *
017     * You should have received a copy of the GNU Lesser General Public
018     * License along with this software; if not, write to the Free
019     * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020     * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
021     */
022    package org.jboss.dna.repository.sequencers;
023    
024    import java.util.Set;
025    import javax.jcr.Node;
026    import javax.jcr.RepositoryException;
027    import javax.jcr.Session;
028    import net.jcip.annotations.ThreadSafe;
029    import org.jboss.dna.common.collection.Problems;
030    import org.jboss.dna.common.component.Component;
031    import org.jboss.dna.repository.observation.NodeChange;
032    import org.jboss.dna.repository.observation.NodeChangeListener;
033    import org.jboss.dna.repository.observation.NodeChanges;
034    import org.jboss.dna.repository.observation.ObservationService;
035    import org.jboss.dna.repository.util.JcrExecutionContext;
036    import org.jboss.dna.repository.util.RepositoryNodePath;
037    
038    /**
039     * The interface for a DNA sequencer, which sequences nodes and their content to extract additional information from the
040     * information.
041     * <p>
042     * Implementations must provide a no-argument constructor.
043     * </p>
044     * 
045     * @author Randall Hauch
046     * @author John Verhaeg
047     */
048    @ThreadSafe
049    public interface Sequencer extends Component<SequencerConfig> {
050    
051        /**
052         * Execute the sequencing operation on the supplied node, which has recently been created or changed. The implementation of
053         * this method is responsible for {@link JcrExecutionContext#getSessionFactory() getting sessions}, modifying the appropriate
054         * nodes, {@link Session#save() saving} any changes made by this sequencer, and {@link Session#logout() closing} all sessions
055         * (and any other acquired resources), even in the case of exceptions.
056         * <p>
057         * The {@link SequencingService} determines the sequencers that should be executed by monitoring the changes to one or more
058         * workspaces (it is a {@link NodeChangeListener} registered with the {@link ObservationService}). Changes in those workspaces
059         * are aggregated for each transaction, and organized into {@link NodeChanges changes for each node}. The SequencingService
060         * then determines for each {@link NodeChange set of changes to a node} the set of full paths to the properties that have
061         * changed and whether those paths {@link SequencerPathExpression#matcher(String) match} the sequencer's
062         * {@link SequencerConfig#getPathExpressions() path expressions}. Each path expression produces the path to the output node,
063         * and these output paths are accumulated and (with the original node that changed, the node change summary, and other
064         * information) supplied to the sequencer via this method.
065         * <p>
066         * It is possible that a sequencer is configured to apply to multiple properties on a node. So, in cases where multiple
067         * properties are changed on a single node (within a single repository transaction), the sequencer will only be executed once.
068         * Also, in such cases the sequencer's configuration may imply multiple output nodes, so it is left to the sequencer to define
069         * the behavior in such cases.
070         * </p>
071         * 
072         * @param input the node that has recently been created or changed; never null
073         * @param sequencedPropertyName the name of the property that caused this sequencer to be executed; never null and never empty
074         * @param changes the immutable summary of changes that occurred on the <code>input</code> node within the transaction; never
075         *        null
076         * @param outputPaths the paths to the nodes where the sequencing content should be placed; never null and never empty, but
077         *        the set may contain paths for non-existant nodes or may reference the <code>input</code> node
078         * @param context the context in which this sequencer is executing; never null
079         * @param problems the interface used for recording problems; never null
080         * @throws RepositoryException if there is a problem while working with the repository
081         * @throws SequencerException if there is an error in this sequencer
082         */
083        void execute( Node input,
084                      String sequencedPropertyName,
085                      NodeChange changes,
086                      Set<RepositoryNodePath> outputPaths,
087                      JcrExecutionContext context,
088                      Problems problems ) throws RepositoryException, SequencerException;
089    
090    }