com.saxonica.ee.stream

Class Inversion

java.lang.Object

com.saxonica.ee.stream.Inversion

public class Inversion
extends java.lang.Object

This class represents an expression that has been "inverted" (in the Jackson sense) so that its execution is push-driven, that is, driven by events from the streamed document. The route taken by these events through the expressions in the expression tree is the "streaming route". Currently this class is simply a wrapper around the Inversion object that represents the path through the expression tree containing expressions that are evaluated in push mode, that is, those that perform downward navigation in the streamed document input.

The expression inversion is represented by a "streaming route", which is the path of nodes in the expression tree, from the root to a leaf, being evaluated in streaming mode. The streaming route starts with a Watch, which is notified by the parser of interesting events. It then proceeds through a series of Feeds which process these events (or items composed from these events) before finally being output to a Receiver which handles the transformation result.

The list of actions is "outermost expression first". This is the opposite of the order in which the events actually pass through the pipeline.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Inversion.PushAction A PushAction is a collection of data that together represents the strategy for how an expression should be evaluated in push mode.

Constructor Summary

Constructors

Constructor and Description
Inversion()

Method Summary

Modifier and Type	Method and Description
void	append(Inversion.PushAction action) Add an action to the end of the streaming route (a subexpression of the currently-last expression, which is therefore first to receive events from the parser)
Inversion	copy() Create a copy of this inverted expression
void	explain(ExpressionPresenter out) Display the streaming route for diagnostic purposes
java.util.List<Inversion.PushAction>	getRoute() Get the list of push actions making up the streaming route
Trigger	getWatch(WatchManager watchManager, Feed parentFeed, XPathContext context) Make a Watch to represent this streaming route.
static Inversion	invertExpression(Expression exp, boolean forGrouping) Compute the Jackson inversion of an expression.
void	prepend(Inversion.PushAction action) Add an action to the start of this streaming route (a parent of the currently-first expression, which is therefore last to receive events from the parser)

Methods inherited from class java.lang.Object

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

Constructor Detail

Inversion

public Inversion()

Method Detail

invertExpression

public static Inversion invertExpression(Expression exp,
                                         boolean forGrouping)
                                  throws XPathException

Compute the Jackson inversion of an expression. The effect is (a) to determine whether the expression is streamable (throwing an exception if not), and (b) to construct the "Streaming route", that is, the path through the expression tree containing expressions that perform downward navigation within the streamed document

Parameters:

exp - the expression to be inverted

forGrouping - true if the expression is the body of a for-each-group that is to be inverted with respect to the grouping variable rather than the context item

Returns:

the inverted expression

Throws:

XPathException - if the expression is not streamable

copy

public Inversion copy()

Create a copy of this inverted expression

Returns:

the copy

append

public void append(Inversion.PushAction action)

Add an action to the end of the streaming route (a subexpression of the currently-last expression, which is therefore first to receive events from the parser)

Parameters:

action - the action to be appended

prepend

public void prepend(Inversion.PushAction action)

Add an action to the start of this streaming route (a parent of the currently-first expression, which is therefore last to receive events from the parser)

Parameters:

action - the action to be prepended

getRoute

public java.util.List<Inversion.PushAction> getRoute()

Get the list of push actions making up the streaming route

Returns:

the list of push actions

getWatch

public Trigger getWatch(WatchManager watchManager,
                        Feed parentFeed,
                        XPathContext context)
                 throws XPathException

Make a Watch to represent this streaming route. The Watch is registered with the WatchManager so it can be notified of events that cause it to be activated

Parameters:

watchManager - the WatchManager (which is known to each Watch under its control)

parentFeed - Maybe null. The destination of events after processing by this Watch

context - XPath context object

Returns:

the Watch

Throws:

XPathException - if an error occurs, e.g. if streaming is not possible.

explain

public void explain(ExpressionPresenter out)
             throws XPathException

Display the streaming route for diagnostic purposes

Parameters:

out - the display destination

Throws:

XPathException