net.sf.saxon.expr.instruct

Class TraceExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.instruct.Instruction

net.sf.saxon.expr.instruct.TraceExpression

All Implemented Interfaces:

javax.xml.transform.SourceLocator, ExportAgent, TailCallReturner, Location, IdentityComparable, InstructionInfo, org.xml.sax.Locator

public class TraceExpression
extends Instruction
implements InstructionInfo

A wrapper expression used to trace expressions in XPath and XQuery.

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
TraceExpression(Expression child) Create a trace expression that traces execution of a given child expression

Method Summary

Modifier and Type	Method and Description
void	checkForUpdatingSubexpressions() Check to ensure that this expression does not contain any inappropriate updating subexpressions.
Expression	copy(RebindingMap rebindings) Copy an expression.
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.
void	export(ExpressionPresenter out) Diagnostic print of expression structure.
int	getCardinality() Determine the static cardinality of the expression.
Expression	getChild()
int	getColumnNumber() Get the column number.
int	getConstructType() Get the construct type.
int	getDependencies() Determine which aspects of the context the expression depends on.
java.lang.String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
InstructionInfo	getInstructionInfo() Get the InstructionInfo details about the construct.
int	getInstructionNameCode() Get the namecode of the instruction for use in diagnostics
ItemType	getItemType() Get the item type of the items returned by evaluating this instruction
int	getLineNumber() Get the line number.
NamespaceResolver	getNamespaceResolver() Get the namespace resolver to supply the namespace context of the instruction that is being traced
int	getNetCost() Return the estimated cost of evaluating an expression.
StructuredQName	getObjectName() Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc.
java.util.Iterator<java.lang.String>	getProperties() Get an iterator over all the properties available.
java.lang.Object	getProperty(java.lang.String name) Get a named property of the instruction/expression
java.lang.String	getPublicId() Get the Public ID
java.lang.String	getSystemId() Get the system ID.
boolean	isUpdatingExpression() Determine whether this is an updating expression as defined in the XQuery update specification
boolean	isVacuousExpression() Determine whether this is a vacuous expression as defined in the XQuery update specification
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
boolean	mayCreateNewNodes() Determine whether this instruction creates new nodes.
java.lang.Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
TailCall	processLeavingTail(XPathContext context) Execute this instruction, with the possibility of returning tail calls if there are any.
Location	saveLocation() Get an immutable copy of this Location object.
void	setChild(Expression child)
void	setConstructType(int type) Set the type of construct.
void	setNamespaceResolver(NamespaceResolver resolver) Set the namespace context for the instruction being traced.
void	setObjectName(StructuredQName qName) Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc.
void	setProperty(java.lang.String name, java.lang.Object value) Set a named property of the instruction/expression
java.lang.String	toShortString() Produce a short string identifying the expression for use in error messages

Methods inherited from class net.sf.saxon.expr.instruct.Instruction

alwaysCreatesNewNodes, assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, getInstructionName, getSourceLocator, isInstruction, isXSLT, process, someOperandCreatesNewNodes

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkPermittedContents, computeDependencies, computeHashCode, computeStaticProperties, dynamicError, effectiveBooleanValue, explain, getConfiguration, getCost, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getPackageData, getParentExpression, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getStreamerName, hasCompatibleStaticContext, hashCode, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isCallOnSystemFunction, isIdentical, isLiftable, isMultiThreaded, isSameExpression, isStaticPropertiesKnown, isSubtreeExpression, markTailFunctionCalls, operandList, operandSparseList, optimize, optimizeChildren, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toString, typeCheck, typeCheckChildren, typeError, unordered, verifyParentPointers, verifyParentPointers

Methods inherited from class java.lang.Object

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

Constructor Detail

TraceExpression

public TraceExpression(Expression child)

Create a trace expression that traces execution of a given child expression

Parameters:

child - the expression to be traced. This will be available to the TraceListener as the value of the "expression" property of the InstructionInfo.

Method Detail

getChild

public Expression getChild()

setChild

public void setChild(Expression child)

operands

public java.lang.Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Specified by:

operands in class Instruction

Returns:

an iterator containing the sub-expressions of this expression

setConstructType

public void setConstructType(int type)

Set the type of construct. This will generally be a constant in class LocationKind

Parameters:

type - an integer code for the type of construct being traced

getConstructType

public int getConstructType()

Get the construct type. This will generally be a constant in class LocationKind

Specified by:

getConstructType in interface InstructionInfo

Overrides:

getConstructType in class Instruction

Returns:

the type of expression, as enumerated in class LocationKind

setNamespaceResolver

public void setNamespaceResolver(NamespaceResolver resolver)

Set the namespace context for the instruction being traced. This is needed if the tracelistener wants to evaluate XPath expressions in the context of the current instruction

Parameters:

resolver - The namespace resolver, or null if none is needed

getNamespaceResolver

public NamespaceResolver getNamespaceResolver()

Get the namespace resolver to supply the namespace context of the instruction that is being traced

Returns:

the namespace resolver, or null if none is in use

setObjectName

public void setObjectName(StructuredQName qName)

Set a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.

Parameters:

qName - the name of the object, or null if not applicable

getObjectName

public StructuredQName getObjectName()

Get a name identifying the object of the expression, for example a function name, template name, variable name, key name, element name, etc. This is used only where the name is known statically.

Specified by:

getObjectName in interface InstructionInfo

Overrides:

getObjectName in class Expression

Returns:

the name of the object, or null if not applicable

setProperty

public void setProperty(java.lang.String name,
                        java.lang.Object value)

Set a named property of the instruction/expression

Parameters:

name - the name of the property

value - the value of the property

getProperty

public java.lang.Object getProperty(java.lang.String name)

Get a named property of the instruction/expression

Specified by:

getProperty in interface InstructionInfo

Overrides:

getProperty in class Expression

Parameters:

name - the name of the property

Returns:

the value of the property

getProperties

public java.util.Iterator<java.lang.String> getProperties()

Get an iterator over all the properties available. The values returned by the iterator will be of type String, and each string can be supplied as input to the getProperty() method to retrieve the value of the property.

Specified by:

getProperties in interface InstructionInfo

Overrides:

getProperties in class Expression

Returns:

an iterator over the properties.

getExpressionName

public java.lang.String getExpressionName()

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Instruction

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.

getInstructionInfo

public InstructionInfo getInstructionInfo()

Get the InstructionInfo details about the construct. This is to satisfy the InstructionInfoProvider interface.

Returns:

the instruction details

copy

public Expression copy(RebindingMap rebindings)

Description copied from class: Expression

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - a mutable list of (old binding, new binding) pairs that is used to update the bindings held in any local variable references that are copied.

Returns:

the copy of the original expression

isUpdatingExpression

public boolean isUpdatingExpression()

Determine whether this is an updating expression as defined in the XQuery update specification

Overrides:

isUpdatingExpression in class Expression

Returns:

true if this is an updating expression

isVacuousExpression

public boolean isVacuousExpression()

Determine whether this is a vacuous expression as defined in the XQuery update specification

Overrides:

isVacuousExpression in class Expression

Returns:

true if this expression is vacuous

checkForUpdatingSubexpressions

public void checkForUpdatingSubexpressions()
                                    throws XPathException

Check to ensure that this expression does not contain any inappropriate updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.

Overrides:

checkForUpdatingSubexpressions in class Expression

Throws:

XPathException - if the expression has a non-permitted updating subexpression

getImplementationMethod

public int getImplementationMethod()

Description copied from class: Instruction

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is prefered. For instructions this is the process() method.

Overrides:

getImplementationMethod in class Instruction

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
                            throws XPathException

Execute this instruction, with the possibility of returning tail calls if there are any. This outputs the trace information via the registered TraceListener, and invokes the instruction being traced.

Specified by:

processLeavingTail in interface TailCallReturner

Specified by:

processLeavingTail in class Instruction

Parameters:

context - the dynamic execution context

Returns:

either null, or a tail call that the caller must invoke on return

Throws:

XPathException

getItemType

public ItemType getItemType()

Get the item type of the items returned by evaluating this instruction

Overrides:

getItemType in class Instruction

Returns:

the static item type of the instruction

getCardinality

public int getCardinality()

Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.

Overrides:

getCardinality in class Expression

Returns:

one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

getDependencies

public int getDependencies()

Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.DEPENDS_ON_CONTEXT_ITEM and StaticProperty.DEPENDS_ON_CURRENT_ITEM. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.

Overrides:

getDependencies in class Expression

Returns:

a set of bit-significant flags identifying the dependencies of the expression

mayCreateNewNodes

public final boolean mayCreateNewNodes()

Determine whether this instruction creates new nodes.

Overrides:

mayCreateNewNodes in class Instruction

Returns:

true if the instruction creates new nodes under some input conditions (or if it can't be proved that it doesn't)

getNetCost

public int getNetCost()

Return the estimated cost of evaluating an expression. For a TraceExpression we return zero, because ideally we don't want trace expressions to affect optimization decisions.

Overrides:

getNetCost in class Instruction

Returns:

zero

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Overrides:

evaluateItem in class Instruction

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Overrides:

iterate in class Instruction

Parameters:

context - supplies the context for evaluation

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getInstructionNameCode

public int getInstructionNameCode()

Description copied from class: Instruction

Get the namecode of the instruction for use in diagnostics

Overrides:

getInstructionNameCode in class Instruction

Returns:

a code identifying the instruction: typically but not always the fingerprint of a name in the XSLT namespace

export

public void export(ExpressionPresenter out)
            throws XPathException

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Specified by:

export in class Expression

Parameters:

out - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

evaluatePendingUpdates

public void evaluatePendingUpdates(XPathContext context,
                                   PendingUpdateList pul)
                            throws XPathException

Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException

Overrides:

evaluatePendingUpdates in class Expression

Parameters:

context - the XPath dynamic evaluation context

pul - the pending update list to which the results should be written

Throws:

XPathException - if evaluation fails

getSystemId

public java.lang.String getSystemId()

Description copied from interface: Location

Get the system ID. This should be the system identifier of an XML external entity; if a stylesheet module comprises multiple external entities, the distinction should be retained. This means, for example, that an instruction in a stylesheet can have a different system identifier from its parent instruction. However, SAX parsers only provide location information at the element level, so when part of an XPath expression is in a different external entity from other parts of the same expression, this distinction is lost.

The system identifier of a node is in general not the same as its base URI. The base URI is affected by xml:base attributes; the system identifier is not.

Specified by:

getSystemId in interface javax.xml.transform.SourceLocator

Specified by:

getSystemId in interface Location

Specified by:

getSystemId in interface org.xml.sax.Locator

Returns:

the system ID, or null if the information is not available.

getColumnNumber

public int getColumnNumber()

Description copied from interface: Location

Get the column number. This column number is relative to the line identified by the line number. Column numbers start at 1.

Specified by:

getColumnNumber in interface javax.xml.transform.SourceLocator

Specified by:

getColumnNumber in interface Location

Specified by:

getColumnNumber in interface org.xml.sax.Locator

Returns:

the column number, or -1 if the information is not available.

getPublicId

public java.lang.String getPublicId()

Description copied from interface: Location

Get the Public ID

Specified by:

getPublicId in interface javax.xml.transform.SourceLocator

Specified by:

getPublicId in interface Location

Specified by:

getPublicId in interface org.xml.sax.Locator

Returns:

usually null

getLineNumber

public int getLineNumber()

Description copied from interface: Location

Get the line number. This line number is relative to the external entity identified by the system identifier. Line numbers start at 1. The value may be an approximation; SAX parsers only provide line number information at the level of element nodes.

Specified by:

getLineNumber in interface javax.xml.transform.SourceLocator

Specified by:

getLineNumber in interface Location

Specified by:

getLineNumber in interface org.xml.sax.Locator

Returns:

the line number, or -1 if the information is not available.

saveLocation

public Location saveLocation()

Description copied from interface: Location

Get an immutable copy of this Location object. By default Location objects may be mutable, so they should not be saved for later use. The result of this operation holds the same location information, but in an immutable form.

Specified by:

saveLocation in interface Location

toShortString

public java.lang.String toShortString()

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class Expression

Returns:

a short string, sufficient to identify the expression