com.saxonica.stream.feed

Class GroupingFeed

java.lang.Object

com.saxonica.stream.feed.ItemFeed

com.saxonica.stream.feed.GroupingFeed

All Implemented Interfaces:

Feed

Direct Known Subclasses:

GroupAdjacentFeed, GroupEndingFeed, GroupStartingFeed

public abstract class GroupingFeed
extends ItemFeed

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
GroupingFeed(GroupVariableReference expression, Feed result, Stack<XPathContext> contextStack)

Method Summary

Methods

Modifier and Type	Method and Description
void	append(Item item) Supply one item towards the streamed input of the expression (that is, one item of the grouping population)
void	close() Finish evaluating the expression.
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

Methods inherited from class com.saxonica.stream.feed.ItemFeed

getContext, getContextStack, getExpression, getPipelineConfiguration, getResult, setPipelineConfiguration

Methods inherited from class java.lang.Object

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

Constructor Detail

GroupingFeed

public GroupingFeed(GroupVariableReference expression,
            Feed result,
            Stack<XPathContext> contextStack)

Method Detail

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 Feed

Overrides:

open in class ItemFeed

Throws:

XPathException

append

public void append(Item item)
            throws XPathException

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

Specified by:

append in interface Feed

Specified by:

append in class ItemFeed

Parameters:

item - the next item from the population

Throws:

XPathException - to report any failure

close

public void close()
           throws XPathException

Description copied from class: ItemFeed

Finish evaluating the expression. The default implementation does nothing.

Specified by:

close in interface Feed

Overrides:

close in class ItemFeed

Throws:

XPathException - if a dynamic error occurs

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