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