Package net.sf.saxon.lib

Interface TraceListener

All Known Implementing Classes:
AbstractTraceListener, ContentHandlerProxy.ContentHandlerProxyTraceListener, TimingTraceListener, TraceEventMulticaster, XQueryTraceListener, XSLTTraceListener
public interface TraceListener
This interface defines methods that are called by Saxon during the execution of a stylesheet or query, if tracing is switched on. Tracing can be switched on by nominating an implementation of this class using the TRACE_LISTENER feature of the TransformerFactory, or using the addTraceListener() method of the Controller.

In normal operation, enter and leave operations are paired, reflecting a simple execution stack. There are two things that can disrupt this: dynamic errors, and parallel evaluation.

If a dynamic error occurs during evaluation of an instruction, there will be enter events with no corresponding leave. If the error is caught, execution may continue. A TraceListener may attempt to recover from this by implementing the checkpoint() and @link #recover} methods.

  • Method Summary

    Modifier and Type
    Method
    Description
    default Object
    checkpoint()
    Method called immediately after the enter(net.sf.saxon.trace.Traceable, java.util.Map<java.lang.String, java.lang.Object>, net.sf.saxon.expr.XPathContext) method corresponding to an xsl:try instruction (or XQuery try/catch).
    default void
    close()
    Method called at the end of each transformation, whether it succeeds or fails.
    default void
    endCurrentItem(Item currentItem)
    Method that is called when an instruction has finished processing a new current item and is ready to select a new current item or revert to the previous current item.
    default void
    endRuleSearch(Object rule, Mode mode, Item item)
    Method called when a rule search has completed.
    default void
    enter(Traceable instruction, Map<String,Object> properties, XPathContext context)
    Method that is called when an instruction in the stylesheet gets processed.
    default void
    leave(Traceable instruction)
    Method that is called after processing an instruction of the stylesheet, that is, after any child instructions have been processed.
    default void
    open(Controller controller)
    Method called at the start of a run-time transformation.
    default void
    recover(Object checkpoint, XPathException err)
    Method called when an error is caught by an xsl:catch (or XQuery try/catch).
    default void
    setOutputDestination(Logger stream)
    Method called to supply the destination for output.
    default void
    startCurrentItem(Item currentItem)
    Method that is called by an instruction that changes the current item in the source document: that is, xsl:for-each, xsl:apply-templates, xsl:for-each-group.
    default void
    startRuleSearch()
    Method called when a search for a template rule is about to start.

  • Method Details

    • setOutputDestination

      default void setOutputDestination(Logger stream)
      Method called to supply the destination for output. The default implementation does nothing.
      Parameters:
      stream - a Logger to which any output produced by the TraceListener should be written
      Since:
      8.0. Changed in 9.6 to accept a Logger.

    • open

      default void open(Controller controller)
      Method called at the start of a run-time transformation. If a transformer is invoked multiple times, the method is called at the start of each transformation. This applies whether the call uses apply-templates, call-template, or invoke-function invocation. The default implementation does nothing.
      Parameters:
      controller - identifies the transformation controller, and provides the listener with access to context and configuration information

    • close

      default void close()
      Method called at the end of each transformation, whether it succeeds or fails. The default implementation does nothing.

    • enter

      default void enter(Traceable instruction, Map<String,Object> properties, XPathContext context)
      Method that is called when an instruction in the stylesheet gets processed. Default implementation does nothing.
      Parameters:
      instruction - gives information about the instruction being executed, and about the context in which it is executed. This object is mutable, so if information from the InstructionInfo is to be retained, it must be copied.
      properties - extra information about the instruction to be included in the trace
      context - the XPath evaluation context

    • leave

      default void leave(Traceable instruction)
      Method that is called after processing an instruction of the stylesheet, that is, after any child instructions have been processed. Default implementation does nothing. Calls on leave() should be properly paired with calls on enter(), but this is not guaranteed if dynamic errors occur.
      Parameters:
      instruction - gives the same information that was supplied to the enter method, though it is not necessarily the same object. Note that the line number of the instruction is that of the start tag in the source stylesheet, not the line number of the end tag.

    • startCurrentItem

      default void startCurrentItem(Item currentItem)
      Method that is called by an instruction that changes the current item in the source document: that is, xsl:for-each, xsl:apply-templates, xsl:for-each-group. The method is called after the enter method for the relevant instruction, and is called once for each item processed. The default implementation does nothing.
      Parameters:
      currentItem - the new current item. Item objects are not mutable; it is safe to retain a reference to the Item for later use.

    • endCurrentItem

      default void endCurrentItem(Item currentItem)
      Method that is called when an instruction has finished processing a new current item and is ready to select a new current item or revert to the previous current item. The method will be called before the leave() method for the instruction that made this item current. Calls on endCurrentItem() should be properly paired with calls on startCurrentItem(), but this is not guaranteed in the event of dynamic errors. The default implementation does nothing.
      Parameters:
      currentItem - the item that was current, whose processing is now complete. This will represent the same underlying item as the corresponding startCurrentItem() call, though it will not necessarily be the same actual object.

    • checkpoint

      default Object checkpoint()
      Method called immediately after the enter(net.sf.saxon.trace.Traceable, java.util.Map<java.lang.String, java.lang.Object>, net.sf.saxon.expr.XPathContext) method corresponding to an xsl:try instruction (or XQuery try/catch). The method may return an object containing checkpoint information, which will be passed to the recover(java.lang.Object, net.sf.saxon.trans.XPathException) method if an error occurs and is caught.
      Returns:
      arbitrary checkpoint information, or null. The default implementation returns null.

    • recover

      default void recover(Object checkpoint, XPathException err)
      Method called when an error is caught by an xsl:catch (or XQuery try/catch).
      Parameters:
      checkpoint - A checkpoint object returned by a previous call to the checkpoint() method.
      err - The error that was caught

    • startRuleSearch

      default void startRuleSearch()
      Method called when a search for a template rule is about to start. The default implementation does nothing.

    • endRuleSearch

      default void endRuleSearch(Object rule, Mode mode, Item item)
      Method called when a rule search has completed. The default implementation does nothing.
      Parameters:
      rule - the rule (or possible built-in ruleset) that has been selected
      mode - the mode in operation
      item - the item that was checked against