com.saxonica.stream.watch

Class GroupingWatch

java.lang.Object

com.saxonica.validate.AbstractWatch

com.saxonica.stream.watch.EventPushingWatch

com.saxonica.stream.watch.GroupingWatch

All Implemented Interfaces:

Watch

Direct Known Subclasses:

GroupAdjacentWatch, GroupEndingWatch, GroupStartingWatch

public abstract class GroupingWatch
extends EventPushingWatch

This feed supports xsl:for-each-group in streaming mode. It is supplied with all the nodes selected by the xsl:for-each-group instruction (in composed form); it decides whether a node is the first in a new group, and if so, triggers the start/end-of-group actions. It also feeds every node into a push pipeline that reflects the processing of the "current-group" variable. The items received by this Feed will generally be supplied by a CopyOfWatch. There is scope for future optimization to prevent the selected nodes being unnecessarily composed in memory. There are thus two destinations into which this class feeds. The first, identified by the usual result variable, receives every item in the group, and is notified of the start and end of a group by calling its open() and close() methods. This destination processes the instructions within the for-each-group instruction before and after the reference to the grouping variable. The second destination, identified by the variable outerFeed, has its open() method called at the beginning of processing the population, and its close() method called at the end of processing the population; its append() method is called with the items that result from evaluation of the for-each-group body.

Constructor Summary

Constructors

Constructor and Description
GroupingWatch(GroupVariableReference expression, Feed out, Stack<XPathContext> contextStack)

Method Summary

Methods

Modifier and Type	Method and Description
void	close() The close() method is called immediately before the Watch is destroyed, that is, when the element whose declaration scopes the constraint implemented by this Watch goes out of scope.
void	endSelectedParentNode(int locationId) Signal that the endElement event has occurred for the element whose startElement event caused the Watch to be activated.
ForEachGroup	getControllingExpression()
protected XPathContext	getLocalContext()
protected abstract boolean	isStartOfNewGroup(boolean atStart, XPathContext context) Determine whether the current item is the start of a new group
void	open() Called at the start of the for-each-group instruction
void	setControllingExpression(ForEachGroup controllingExpression)
void	setOuterFeed(Feed out) Set the outer feed; the feed to be notified (via its open() and close() methods) of the start of the grouping population and the end of the grouping population
void	setWatchManager(WatchManager watchManager)
Receiver	startSelectedParentNode(FleetingNode node, int locationId) Supply one item towards the streamed input of the expression (that is, one item of the grouping population)

Methods inherited from class com.saxonica.stream.watch.EventPushingWatch

getContext, getContextStack, getExpression, getParentExpressionFeed, getResult, setParentExpressionFeed

Methods inherited from class com.saxonica.validate.AbstractWatch

getAnchorNode, getNamespaceResolver, getPipelineConfiguration, getSelection, notifySelectedLeafNode, setAnchorNode, setNamespaceResolver, setPipelineConfiguration, setSelection

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GroupingWatch

public GroupingWatch(GroupVariableReference expression,
             Feed out,
             Stack<XPathContext> contextStack)

Method Detail

setWatchManager

public void setWatchManager(WatchManager watchManager)

setOuterFeed

public void setOuterFeed(Feed out)

Set the outer feed; the feed to be notified (via its open() and close() methods) of the start of the grouping population and the end of the grouping population

Parameters:

out - the outer feed

getLocalContext

protected XPathContext getLocalContext()

setControllingExpression

public void setControllingExpression(ForEachGroup controllingExpression)

getControllingExpression

public ForEachGroup getControllingExpression()

open

public void open()
          throws XPathException

Called at the start of the for-each-group instruction

Specified by:

open in interface Watch

Overrides:

open in class EventPushingWatch

Throws:

XPathException

startSelectedParentNode

public Receiver startSelectedParentNode(FleetingNode node,
                               int locationId)
                                 throws XPathException

Supply one item towards the streamed input of the expression (that is, one item of the grouping population)

Parameters:

node - the next item from the population

locationId - the location associated with the element or document node (may be the location of the instruction that created it)

Returns:

a Receiver to be notified of all events starting with the startElement/startDocument event for the matched element, and ending with the endElement event for that element; or null if this feature is not required.

Throws:

XPathException - May be raised if a dynamic error occurs

endSelectedParentNode

public void endSelectedParentNode(int locationId)
                           throws XPathException

Signal that the endElement event has occurred for the element whose startElement event caused the Watch to be activated.

Parameters:

locationId - the location of the element

Throws:

XPathException - May be raised if a constraint implemented by this Watch is violated

close

public void close()
           throws XPathException

Description copied from class: AbstractWatch

The close() method is called immediately before the Watch is destroyed, that is, when the element whose declaration scopes the constraint implemented by this Watch goes out of scope. The default implementation does nothing.

Specified by:

close in interface Watch

Overrides:

close in class EventPushingWatch

Throws:

XPathException

isStartOfNewGroup

protected abstract boolean isStartOfNewGroup(boolean atStart,
                        XPathContext context)
                                      throws XPathException

Determine whether the current item is the start of a new group

Parameters:

atStart - true if this item is the first in the population

context - the evaluation context. The item in question will be the context item

Returns:

true if this item is to be the first in a new group

Throws:

XPathException - if a dynamic error occurs