org.jboss.dna.repository.sequencers
Interface Sequencer

All Superinterfaces:

Component<SequencerConfig>

All Known Implementing Classes:

StreamSequencerAdapter

@ThreadSafe
public interface Sequencer
extends Component<SequencerConfig>

The interface for a DNA sequencer, which sequences nodes and their content to extract additional information from the information.

Implementations must provide a no-argument constructor.

Author:

Randall Hauch

Method Summary

void	execute(javax.jcr.Node input, java.lang.String sequencedPropertyName, NodeChange changes, java.util.Set<RepositoryNodePath> outputPaths, ExecutionContext context, ProgressMonitor progress) Execute the sequencing operation on the supplied node, which has recently been created or changed.

Methods inherited from interface org.jboss.dna.common.component.Component

getConfiguration, setConfiguration

Method Detail

execute

void execute(javax.jcr.Node input,
             java.lang.String sequencedPropertyName,
             NodeChange changes,
             java.util.Set<RepositoryNodePath> outputPaths,
             ExecutionContext context,
             ProgressMonitor progress)
             throws javax.jcr.RepositoryException,
                    SequencerException

Execute the sequencing operation on the supplied node, which has recently been created or changed. The implementation of this method is responsible for getting sessions, modifying the appropriate nodes, saving any changes made by this sequencer, and closing all sessions (and any other acquired resources), even in the case of cancellation or exceptions.

The SequencingService determines the sequencers that should be executed by monitoring the changes to one or more workspaces (it is a NodeChangeListener registered with the ObservationService). Changes in those workspaces are aggregated for each transaction, and organized into changes for each node. The SequencingService then determines for each set of changes to a node the set of full paths to the properties that have changed and whether those paths match the sequencer's path expressions. Each path expression produces the path to the output node, and these output paths are accumulated and (with the original node that changed, the node change summary, and other information) supplied to the sequencer via this method.

It is possible that a sequencer is configured to apply to multiple properties on a node. So, in cases where multiple properties are changed on a single node (within a single repository transaction), the sequencer will only be executed once. Also, in such cases the sequencer's configuration may imply multiple output nodes, so it is left to the sequencer to define the behavior in such cases.

This operation should report progress to the supplied ProgressMonitor. At the beginning of the operation, call ProgressMonitor.beginTask(double, org.jboss.dna.common.i18n.I18n, Object...) with a meaningful message describing the operation and a total for the amount of work that will be done by this sequencer. Then perform the sequencing work, periodically reporting work by specifying the amount of work that has was just completed or by creating a subtask and reporting work against that subtask monitor.

The implementation should also periodically check whether the operation has been cancelled. If this method returns true, the implementation should abort all work as soon as possible and close any resources that were acquired or opened.

Finally, the implementation should call ProgressMonitor.done() when the operation has finished.

Parameters:

input - the node that has recently been created or changed; never null

sequencedPropertyName - the name of the property that caused this sequencer to be executed; never null and never empty

changes - the immutable summary of changes that occurred on the input node within the transaction; never null

outputPaths - the paths to the nodes where the sequencing content should be placed; never null and never empty, but the set may contain paths for non-existant nodes or may reference the input node

context - the context in which this sequencer is executing; never null

progress - the progress monitor that should be kept updated with the sequencer's progress and that should be frequently consulted as to whether this operation has been cancelled.

Throws:

javax.jcr.RepositoryException - if there is a problem while working with the repository

SequencerException - if there is an error in this sequencer