Class StreamingAdjunct
- Direct Known Subclasses:
ApplyImportsAdjunct
,ApplyTemplatesAdjunct
,AscentFunctionCallAdjunct
,AtomicSequenceConverterAdjunct
,AxisExpressionAdjunct
,CallTemplateAdjunct
,CodepointsToStringStreamer
,ComposingAdjunct
,ContextItemExprAdjunct
,CopyAdjunct
,CurrentGroupStreamer
,DeepEqualStreamer
,DistinctValuesStreamer
,EmptyTextNodeRemoverAdjunct
,FoldStreamer
,ForExpressionAdjunct
,ForkAdjunct
,GeneralComparisonAdjunct
,IndexOfStreamer
,InspectionAdjunct
,IsLastExprAdjunct
,LastStreamer
,LetExpressionAdjunct
,LiteralAdjunct
,MapEntryStreamer
,MergeInstrAdjunct
,MinimaxStreamer
,NewMapStreamer
,NextIterationAdjunct
,NextMatchAdjunct
,ParentConstructorAdjunct
,ReverseStreamer
,RootExpressionAdjunct
,RootStreamer
,SequenceInstrAdjunct
,SimpleNodeConstructorAdjunct
,SingletonAtomizerAdjunct
,SortExpressionAdjunct
,TransmissionAdjunct
,UseAttributeSetAdjunct
,UserFunctionCallAdjunct
,XmlToJsonFnStreamer
Expression
with methods used at compile-time
to support streaming, by generating a Watch
that allows the expression to be evaluated in push mode.
The default implementation is adequate only for expressions that take single items as their input. For other kinds of expression, either a WatchMaker or FeedMaker, or both, need to be supplied. If the input sequence is atomized (as with the sum() function), then only a FeedMaker is required; a TypedValueWatch will automatically be added to the Streaming Route to perform atomization of the supplied sequence. For expressions that do not perform atomization, both a WatchMaker (for use when the input is striding or consuming) and a FeedMaker (for use when it is climbing or grounded) need to be provided.
Neither method should be called in cases where streamability analysis has decided that the expression is not streamable. In such cases the methods may throw an exception.
There is a fallback implementation that allows any expression to be evaluated as a Feed, but it involves buffering the input in memory, and performing an implicit copy-of() to create a grounded copy, so it is only really suitable for the case where the input is a single atomic value.
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptioncomputeStreamability
(ContextItemStaticInfoEE contextInfo, List<String> reasons) Compute the posture and sweep of this expression as defined in the W3C streamability specifications.static Map
<String, Supplier<StreamingAdjunct>> static int
findConsumingArg
(Expression expression, int knownConsumingArg) Find which operand of an expression is the consuming operand.static String
Get the Saxon Configurationprotected FeedMaker
getDefaultFeedMaker
(int arg) Get a FeedMaker which will generate a feed to handle streamed input of operand "arg".Get the expression being processed by this StreamingAdjunctgetFeedMaker
(int arg) Get a FeedMaker, a factory class that creates a Feed to evaluate this expression in streaming mode.getWatchMaker
(boolean forGrouping) Get a WatchMaker, a factory class that creates a Watch to evaluate this expression in streaming mode.static StreamingAdjunct
makeStreamingAdjunct
(Configuration config, Expression exp) Make a streaming adjunct for a particular expression.void
setConfiguration
(Configuration config) Set the Saxon Configurationvoid
setExpression
(Expression expression) Set the expression being processed by this StreamingAdjuncttoStreamingPattern
(Configuration config) Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)
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Constructor Details
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StreamingAdjunct
public StreamingAdjunct()
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Method Details
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emptyAdjunctMap
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makeStreamingAdjunct
Make a streaming adjunct for a particular expression.- Parameters:
config
- the Saxon Configurationexp
- the expression to be compiled- Returns:
- the compiler for this kind of expression
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setConfiguration
Set the Saxon Configuration- Parameters:
config
- the Configuration
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getConfiguration
Get the Saxon Configuration- Returns:
- the configuration
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setExpression
Set the expression being processed by this StreamingAdjunct- Parameters:
expression
- the expression being processed
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getExpression
Get the expression being processed by this StreamingAdjunct- Returns:
- the expression being processed
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computeStreamability
public PostureAndSweep computeStreamability(ContextItemStaticInfoEE contextInfo, List<String> reasons) Compute the posture and sweep of this expression as defined in the W3C streamability specifications. This must be implemented in all subclasses that don't use the general streamability rules. The implementation should have the side-effect of computing the streamability of all subexpressions, recursively.- Parameters:
contextInfo
- Information about the context item type and posturereasons
- the caller may supply a list, in which case the implementation may add to this; the contents are human-readable messages explaining why the expression is not streamable.- Returns:
- the posture and sweep of the expression
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findConsumingArg
public static int findConsumingArg(Expression expression, int knownConsumingArg) throws XPathException Find which operand of an expression is the consuming operand. Helper method for use by subclasses- Parameters:
expression
- the expressionknownConsumingArg
- index of the consuming operand if known, otherwise -1- Returns:
- index identifying the consuming operand
- Throws:
XPathException
- if there is no consuming operand
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toStreamingPattern
Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)- Parameters:
config
- the Saxon configuration- Returns:
- the equivalent pattern if conversion succeeds; otherwise null
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getWatchMaker
Get a WatchMaker, a factory class that creates a Watch to evaluate this expression in streaming mode. This method will only be called if the getImplementationMethod() method of the expression includes the valueExpression.WATCH_METHOD
- Parameters:
forGrouping
- true if the selected items are being grouped- Returns:
- a Watchmaker to evaluate the expression, or null if it is not streamable with respect to the specificed argument.
- Throws:
XPathException
- in the event of a failure
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getFeedMaker
Get a FeedMaker, a factory class that creates a Feed to evaluate this expression in streaming mode. In many cases the StreamingAdjunct is itself a FeedMaker, in which case it returns itself. But where an expression has several operands, it will typically create different feeds depending on which argument is the streamed input, and in such cases the individual StreamingAdjunct makes the decision which feed to use, by returning an appropriate FeedMaker.- Parameters:
arg
- identifies the argument with respect to which the expression is to be inverted: usually 0 to indicate the first argument is the value that is streamed. Argument numbering is the same as the sequence of arguments/operands returned by the methodExpression.operands()
- Returns:
- a FeedMaker to evaluate the expression, or null if it is not streamable with respect to the specificed argument.
- Throws:
XPathException
- in the event of a failure
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getDefaultFeedMaker
Get a FeedMaker which will generate a feed to handle streamed input of operand "arg".- Parameters:
arg
- identifies which operand of the expression is the streamed (consuming) input- Returns:
- a FeedMaker
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genId
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