Package 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:
SourceLocator, ExportAgent, TailCallReturner, Locatable, Location, IdentityComparable, InstructionInfo, Locator
public class TraceExpression extends Instruction implements InstructionInfo
A wrapper expression used to trace expressions in XPath and XQuery.

  • Constructor Details

    • 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 Details

    • getChild

      public Expression getChild()

    • setChild

      public void setChild(Expression child)

    • operands

      public 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(String name, 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 Object getProperty(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 Iterator<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 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.

    • getStreamerName

      public String getStreamerName()
      Get the (partial) name of a class that supports streaming of this kind of expression
      Overrides:
      getStreamerName in class Expression
      Returns:
      the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class

    • 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 potentially 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 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 Location
      Specified by:
      getSystemId in interface Locator
      Specified by:
      getSystemId in interface SourceLocator
      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 Location
      Specified by:
      getColumnNumber in interface Locator
      Specified by:
      getColumnNumber in interface SourceLocator
      Returns:
      the column number, or -1 if the information is not available.

    • getPublicId

      public String getPublicId()
      Description copied from interface: Location
      Get the Public ID
      Specified by:
      getPublicId in interface Location
      Specified by:
      getPublicId in interface Locator
      Specified by:
      getPublicId in interface SourceLocator
      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 Location
      Specified by:
      getLineNumber in interface Locator
      Specified by:
      getLineNumber in interface SourceLocator
      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 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