org.apache.xpath.axes
Class WalkerFactory

java.lang.Object
  org.apache.xpath.axes.WalkerFactory

public class WalkerFactory

extends Object

This class is both a factory for XPath location path expressions, which are built from the opcode map output, and an analysis engine for the location path expressions in order to provide optimization hints.

Field Summary

static int	BIT_ANCESTOR Bit is on if any of the walkers contain an ancestor step.
static int	BIT_ANCESTOR_OR_SELF Bit is on if any of the walkers contain an ancestor-or-self step.
static int	BIT_ANY_DESCENDANT_FROM_ROOT Found "//foo" pattern
static int	BIT_ATTRIBUTE Bit is on if any of the walkers contain an attribute step.
static int	BIT_BACKWARDS_SELF Bit is on if any of the walkers can go backwards in document order from the context node.
static int	BIT_CHILD Bit is on if any of the walkers contain a child step.
static int	BIT_DESCENDANT Bit is on if any of the walkers contain a descendant step.
static int	BIT_DESCENDANT_OR_SELF Bit is on if any of the walkers contain a descendant-or-self step.
static int	BIT_FILTER Bit is on if any of the walkers contain a filter (i.e. id(), extension function, etc.) step.
static int	BIT_FOLLOWING Bit is on if any of the walkers contain a following step.
static int	BIT_FOLLOWING_SIBLING Bit is on if any of the walkers contain a following-sibiling step.
static int	BIT_MATCH_PATTERN Bit is on if the expression is a match pattern.
static int	BIT_NAMESPACE Bit is on if any of the walkers contain a namespace step.
static int	BIT_NODETEST_ANY Bit is on if any of the walkers contain an node() test.
static int	BIT_PARENT Bit is on if any of the walkers contain a parent step.
static int	BIT_PRECEDING Bit is on if any of the walkers contain a preceding step.
static int	BIT_PRECEDING_SIBLING Bit is on if any of the walkers contain a preceding-sibling step.
static int	BIT_PREDICATE Bit is on if the expression contains a top-level predicate.
static int	BIT_ROOT Bit is on if any of the walkers contain a root step.
static int	BIT_SELF Bit is on if any of the walkers contain a self step.
static int	BITMASK_TRAVERSES_OUTSIDE_SUBTREE If any of these bits are on, the expression may likely traverse outside the given subtree.
static int	BITS_COUNT First 8 bits are the number of top-level location steps.
static int	BITS_RESERVED 4 bits are reserved for future use.
(package private) static boolean	DEBUG_ITERATOR_CREATION Set to true for diagnostics about iterator creation
(package private) static boolean	DEBUG_PATTERN_CREATION Set to true for diagnostics about walker creation
(package private) static boolean	DEBUG_WALKER_CREATION Set to true for diagnostics about walker creation

Constructor Summary

WalkerFactory()

Method Summary

private static int	analyze(Compiler compiler, int stepOpCodePos, int stepIndex) Analyze the location path and return 32 bits that give information about the location path as a whole.
(package private) static boolean	analyzePredicate(Compiler compiler, int opPos, int stepType) Analyze a step and give information about it's predicates.
static boolean	canCrissCross(int analysis)
static boolean	canSkipSubtrees(int analysis)
private static StepPattern	createDefaultStepPattern(Compiler compiler, int opPos, MatchPatternIterator mpi, int analysis, StepPattern tail, StepPattern head) Create a StepPattern that is contained within a LocationPath.
private static AxesWalker	createDefaultWalker(Compiler compiler, int opPos, WalkingIterator lpi, int analysis) Create the proper Walker from the axes type.
static void	diagnoseIterator(String name, int analysis, Compiler compiler)
(package private) static boolean	functionProximateOrContainsProximate(Compiler compiler, int opPos)
static int	getAnalysisBitFromAxes(int axis) Get a corresponding BIT_XXX from an axis.
static String	getAnalysisString(int analysis)
static int	getAxisFromStep(Compiler compiler, int stepOpCodePos) Special purpose function to see if we can optimize the pattern for a DescendantIterator.
static int	getStepCount(int analysis)
static boolean	hasPredicate(int analysis)
static boolean	isAbsolute(int analysis)
static boolean	isDownwardAxisOfMany(int axis) Tell if the given axis goes downword.
private static boolean	isNaturalDocOrder(Compiler compiler, int stepOpCodePos, int stepIndex, int analysis) Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.
static boolean	isNaturalDocOrder(int analysis) Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.
static boolean	isOneStep(int analysis)
private static boolean	isOptimizableForDescendantIterator(Compiler compiler, int stepOpCodePos, int stepIndex) Special purpose function to see if we can optimize the pattern for a DescendantIterator.
(package private) static boolean	isProximateInnerExpr(Compiler compiler, int opPos)
static boolean	isSet(int analysis, int bits)
static boolean	isWild(int analysis)
(package private) static AxesWalker	loadOneWalker(WalkingIterator lpi, Compiler compiler, int stepOpCodePos) This method is for building an array of possible levels where the target element(s) could be found for a match.
(package private) static StepPattern	loadSteps(MatchPatternIterator mpi, Compiler compiler, int stepOpCodePos, int stepIndex) Read a LocationPath as a generalized match pattern.
(package private) static AxesWalker	loadWalkers(WalkingIterator lpi, Compiler compiler, int stepOpCodePos, int stepIndex) This method is for building an array of possible levels where the target element(s) could be found for a match.
static boolean	mightBeProximate(Compiler compiler, int opPos, int stepType) Tell if the predicates need to have proximity knowledge.
static DTMIterator	newDTMIterator(Compiler compiler, int opPos, boolean isTopLevel) Create a new LocPathIterator iterator.
static boolean	walksAncestors(int analysis)
static boolean	walksAttributes(int analysis)
static boolean	walksChildren(int analysis)
static boolean	walksChildrenAndExtraAndSelfOnly(int analysis)
static boolean	walksChildrenOnly(int analysis)
static boolean	walksDescendants(int analysis)
static boolean	walksDescendantsAndExtraAndSelfOnly(int analysis)
static boolean	walksDownExtraOnly(int analysis)
static boolean	walksDownOnly(int analysis)
static boolean	walksExtraNodes(int analysis)
static boolean	walksExtraNodesOnly(int analysis)
static boolean	walksFilteredList(int analysis)
static boolean	walksFollowingOnlyMaybeAbsolute(int analysis)
static boolean	walksInDocOrder(int analysis)
static boolean	walksNamespaces(int analysis)
static boolean	walksSelfOnly(int analysis)
static boolean	walksSideways(int analysis)
static boolean	walksSubtree(int analysis)
static boolean	walksSubtreeOnly(int analysis)
static boolean	walksSubtreeOnlyFromRootOrContext(int analysis)
static boolean	walksSubtreeOnlyMaybeAbsolute(int analysis)
static boolean	walksUp(int analysis)
static boolean	walksUpOnly(int analysis)

Methods inherited from class java.lang.Object

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

Field Detail

DEBUG_PATTERN_CREATION

static final boolean DEBUG_PATTERN_CREATION

Set to true for diagnostics about walker creation

See Also:

Constant Field Values

DEBUG_WALKER_CREATION

static final boolean DEBUG_WALKER_CREATION

Set to true for diagnostics about walker creation

See Also:

Constant Field Values

DEBUG_ITERATOR_CREATION

static final boolean DEBUG_ITERATOR_CREATION

Set to true for diagnostics about iterator creation

See Also:

Constant Field Values

BITS_COUNT

public static final int BITS_COUNT

First 8 bits are the number of top-level location steps. Hopefully there will never be more that 255 location steps!!!

See Also:

Constant Field Values

BITS_RESERVED

public static final int BITS_RESERVED

4 bits are reserved for future use.

See Also:

Constant Field Values

BIT_PREDICATE

public static final int BIT_PREDICATE

Bit is on if the expression contains a top-level predicate.

See Also:

Constant Field Values

BIT_ANCESTOR

public static final int BIT_ANCESTOR

Bit is on if any of the walkers contain an ancestor step.

See Also:

Constant Field Values

BIT_ANCESTOR_OR_SELF

public static final int BIT_ANCESTOR_OR_SELF

Bit is on if any of the walkers contain an ancestor-or-self step.

See Also:

Constant Field Values

BIT_ATTRIBUTE

public static final int BIT_ATTRIBUTE

Bit is on if any of the walkers contain an attribute step.

See Also:

Constant Field Values

BIT_CHILD

public static final int BIT_CHILD

Bit is on if any of the walkers contain a child step.

See Also:

Constant Field Values

BIT_DESCENDANT

public static final int BIT_DESCENDANT

Bit is on if any of the walkers contain a descendant step.

See Also:

Constant Field Values

BIT_DESCENDANT_OR_SELF

public static final int BIT_DESCENDANT_OR_SELF

Bit is on if any of the walkers contain a descendant-or-self step.

See Also:

Constant Field Values

BIT_FOLLOWING

public static final int BIT_FOLLOWING

Bit is on if any of the walkers contain a following step.

See Also:

Constant Field Values

BIT_FOLLOWING_SIBLING

public static final int BIT_FOLLOWING_SIBLING

Bit is on if any of the walkers contain a following-sibiling step.

See Also:

Constant Field Values

BIT_NAMESPACE

public static final int BIT_NAMESPACE

Bit is on if any of the walkers contain a namespace step.

See Also:

Constant Field Values

BIT_PARENT

public static final int BIT_PARENT

Bit is on if any of the walkers contain a parent step.

See Also:

Constant Field Values

BIT_PRECEDING

public static final int BIT_PRECEDING

Bit is on if any of the walkers contain a preceding step.

See Also:

Constant Field Values

BIT_PRECEDING_SIBLING

public static final int BIT_PRECEDING_SIBLING

Bit is on if any of the walkers contain a preceding-sibling step.

See Also:

Constant Field Values

BIT_SELF

public static final int BIT_SELF

Bit is on if any of the walkers contain a self step.

See Also:

Constant Field Values

BIT_FILTER

public static final int BIT_FILTER

Bit is on if any of the walkers contain a filter (i.e. id(), extension function, etc.) step.

See Also:

Constant Field Values

BIT_ROOT

public static final int BIT_ROOT

Bit is on if any of the walkers contain a root step.

See Also:

Constant Field Values

BITMASK_TRAVERSES_OUTSIDE_SUBTREE

public static final int BITMASK_TRAVERSES_OUTSIDE_SUBTREE

If any of these bits are on, the expression may likely traverse outside the given subtree.

See Also:

Constant Field Values

BIT_BACKWARDS_SELF

public static final int BIT_BACKWARDS_SELF

Bit is on if any of the walkers can go backwards in document order from the context node.

See Also:

Constant Field Values

BIT_ANY_DESCENDANT_FROM_ROOT

public static final int BIT_ANY_DESCENDANT_FROM_ROOT

Found "//foo" pattern

See Also:

Constant Field Values

BIT_NODETEST_ANY

public static final int BIT_NODETEST_ANY

Bit is on if any of the walkers contain an node() test. This is really only useful if the count is 1.

See Also:

Constant Field Values

BIT_MATCH_PATTERN

public static final int BIT_MATCH_PATTERN

Bit is on if the expression is a match pattern.

See Also:

Constant Field Values

Constructor Detail

WalkerFactory

public WalkerFactory()

Method Detail

loadOneWalker

static AxesWalker loadOneWalker(WalkingIterator lpi,
                                Compiler compiler,
                                int stepOpCodePos)
                         throws javax.xml.transform.TransformerException

This method is for building an array of possible levels where the target element(s) could be found for a match.

Parameters:

lpi - The owning location path iterator.

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

Returns:

non-null AxesWalker derivative.

Throws:

javax.xml.transform.TransformerException

loadWalkers

static AxesWalker loadWalkers(WalkingIterator lpi,
                              Compiler compiler,
                              int stepOpCodePos,
                              int stepIndex)
                       throws javax.xml.transform.TransformerException

This method is for building an array of possible levels where the target element(s) could be found for a match.

Parameters:

lpi - The owning location path iterator object.

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

stepIndex - The top-level step index withing the iterator.

Returns:

non-null AxesWalker derivative.

Throws:

javax.xml.transform.TransformerException

isSet

public static boolean isSet(int analysis,
                            int bits)

diagnoseIterator

public static void diagnoseIterator(String name,
                                    int analysis,
                                    Compiler compiler)

newDTMIterator

public static DTMIterator newDTMIterator(Compiler compiler,
                                         int opPos,
                                         boolean isTopLevel)
                                  throws javax.xml.transform.TransformerException

Create a new LocPathIterator iterator. The exact type of iterator returned is based on an analysis of the XPath operations.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

opPos - The position of the operation code for this itterator.

Returns:

non-null reference to a LocPathIterator or derivative.

Throws:

javax.xml.transform.TransformerException

getAxisFromStep

public static int getAxisFromStep(Compiler compiler,
                                  int stepOpCodePos)
                           throws javax.xml.transform.TransformerException

Special purpose function to see if we can optimize the pattern for a DescendantIterator.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

Returns:

32 bits as an integer that give information about the location path as a whole.

Throws:

javax.xml.transform.TransformerException

getAnalysisBitFromAxes

public static int getAnalysisBitFromAxes(int axis)

Get a corresponding BIT_XXX from an axis.

Parameters:

axis - One of Axis.ANCESTOR, etc.

Returns:

One of BIT_ANCESTOR, etc.

functionProximateOrContainsProximate

static boolean functionProximateOrContainsProximate(Compiler compiler,
                                                    int opPos)

isProximateInnerExpr

static boolean isProximateInnerExpr(Compiler compiler,
                                    int opPos)

mightBeProximate

public static boolean mightBeProximate(Compiler compiler,
                                       int opPos,
                                       int stepType)
                                throws javax.xml.transform.TransformerException

Tell if the predicates need to have proximity knowledge.

Throws:

javax.xml.transform.TransformerException

isOptimizableForDescendantIterator

private static boolean isOptimizableForDescendantIterator(Compiler compiler,
                                                          int stepOpCodePos,
                                                          int stepIndex)
                                                   throws javax.xml.transform.TransformerException

Special purpose function to see if we can optimize the pattern for a DescendantIterator.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

stepIndex - The top-level step index withing the iterator.

Returns:

32 bits as an integer that give information about the location path as a whole.

Throws:

javax.xml.transform.TransformerException

analyze

private static int analyze(Compiler compiler,
                           int stepOpCodePos,
                           int stepIndex)
                    throws javax.xml.transform.TransformerException

Analyze the location path and return 32 bits that give information about the location path as a whole. See the BIT_XXX constants for meaning about each of the bits.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

stepIndex - The top-level step index withing the iterator.

Returns:

32 bits as an integer that give information about the location path as a whole.

Throws:

javax.xml.transform.TransformerException

isDownwardAxisOfMany

public static boolean isDownwardAxisOfMany(int axis)

Tell if the given axis goes downword. Bogus name, if you can think of a better one, please do tell. This really has to do with inverting attribute axis.

Parameters:

axis - One of Axis.XXX.

Returns:

true if the axis is not a child axis and does not go up from the axis root.

loadSteps

static StepPattern loadSteps(MatchPatternIterator mpi,
                             Compiler compiler,
                             int stepOpCodePos,
                             int stepIndex)
                      throws javax.xml.transform.TransformerException

Read a LocationPath as a generalized match pattern. What this means is that the LocationPath is read backwards, as a test on a given node, to see if it matches the criteria of the selection, and ends up at the context node. Essentially, this is a backwards query from a given node, to find the context node.

So, the selection "foo/daz[2]" is, in non-abreviated expanded syntax, "self::node()/following-sibling::foo/child::daz[position()=2]". Taking this as a match pattern for a probable node, it works out to "self::daz/parent::foo[child::daz[position()=2 and isPrevStepNode()] precedingSibling::node()[isContextNodeOfLocationPath()]", adding magic isPrevStepNode and isContextNodeOfLocationPath operations. Predicates in the location path have to be executed by the following step, because they have to know the context of their execution.

Parameters:

mpi - The MatchPatternIterator to which the steps will be attached.

compiler - The compiler that holds the syntax tree/op map to construct from.

stepOpCodePos - The current op code position within the opmap.

stepIndex - The top-level step index withing the iterator.

Returns:

A StepPattern object, which may contain relative StepPatterns.

Throws:

javax.xml.transform.TransformerException

createDefaultStepPattern

private static StepPattern createDefaultStepPattern(Compiler compiler,
                                                    int opPos,
                                                    MatchPatternIterator mpi,
                                                    int analysis,
                                                    StepPattern tail,
                                                    StepPattern head)
                                             throws javax.xml.transform.TransformerException

Create a StepPattern that is contained within a LocationPath.

Parameters:

compiler - The compiler that holds the syntax tree/op map to construct from.

mpi - The MatchPatternIterator to which the steps will be attached.

analysis - 32 bits of analysis, from which the type of AxesWalker may be influenced.

tail - The step that is the first step analyzed, but the last step in the relative match linked list, i.e. the tail. May be null.

head - The step that is the current head of the relative match step linked list. May be null.

Returns:

the head of the list.

Throws:

javax.xml.transform.TransformerException

analyzePredicate

static boolean analyzePredicate(Compiler compiler,
                                int opPos,
                                int stepType)
                         throws javax.xml.transform.TransformerException

Analyze a step and give information about it's predicates. Right now this just returns true or false if the step has a predicate.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

opPos - The opcode position for the step.

stepType - The type of step, one of OP_GROUP, etc.

Returns:

true if step has a predicate.

Throws:

javax.xml.transform.TransformerException

createDefaultWalker

private static AxesWalker createDefaultWalker(Compiler compiler,
                                              int opPos,
                                              WalkingIterator lpi,
                                              int analysis)

Create the proper Walker from the axes type.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

opPos - The opcode position for the step.

lpi - The owning location path iterator.

analysis - 32 bits of analysis, from which the type of AxesWalker may be influenced.

Returns:

non-null reference to AxesWalker derivative.

Throws:

RuntimeException - if the input is bad.

getAnalysisString

public static String getAnalysisString(int analysis)

hasPredicate

public static boolean hasPredicate(int analysis)

isWild

public static boolean isWild(int analysis)

walksAncestors

public static boolean walksAncestors(int analysis)

walksAttributes

public static boolean walksAttributes(int analysis)

walksNamespaces

public static boolean walksNamespaces(int analysis)

walksChildren

public static boolean walksChildren(int analysis)

walksDescendants

public static boolean walksDescendants(int analysis)

walksSubtree

public static boolean walksSubtree(int analysis)

walksSubtreeOnlyMaybeAbsolute

public static boolean walksSubtreeOnlyMaybeAbsolute(int analysis)

walksSubtreeOnly

public static boolean walksSubtreeOnly(int analysis)

walksFilteredList

public static boolean walksFilteredList(int analysis)

walksSubtreeOnlyFromRootOrContext

public static boolean walksSubtreeOnlyFromRootOrContext(int analysis)

walksInDocOrder

public static boolean walksInDocOrder(int analysis)

walksFollowingOnlyMaybeAbsolute

public static boolean walksFollowingOnlyMaybeAbsolute(int analysis)

walksUp

public static boolean walksUp(int analysis)

walksSideways

public static boolean walksSideways(int analysis)

walksExtraNodes

public static boolean walksExtraNodes(int analysis)

walksExtraNodesOnly

public static boolean walksExtraNodesOnly(int analysis)

isAbsolute

public static boolean isAbsolute(int analysis)

walksChildrenOnly

public static boolean walksChildrenOnly(int analysis)

walksChildrenAndExtraAndSelfOnly

public static boolean walksChildrenAndExtraAndSelfOnly(int analysis)

walksDescendantsAndExtraAndSelfOnly

public static boolean walksDescendantsAndExtraAndSelfOnly(int analysis)

walksSelfOnly

public static boolean walksSelfOnly(int analysis)

walksUpOnly

public static boolean walksUpOnly(int analysis)

walksDownOnly

public static boolean walksDownOnly(int analysis)

walksDownExtraOnly

public static boolean walksDownExtraOnly(int analysis)

canSkipSubtrees

public static boolean canSkipSubtrees(int analysis)

canCrissCross

public static boolean canCrissCross(int analysis)

isNaturalDocOrder

public static boolean isNaturalDocOrder(int analysis)

Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.

Parameters:

analysis - The general analysis of the pattern.

Returns:

true if the walk can be done in natural order.

Throws:

javax.xml.transform.TransformerException

isNaturalDocOrder

private static boolean isNaturalDocOrder(Compiler compiler,
                                         int stepOpCodePos,
                                         int stepIndex,
                                         int analysis)
                                  throws javax.xml.transform.TransformerException

Tell if the pattern can be 'walked' with the iteration steps in natural document order, without duplicates.

Parameters:

compiler - non-null reference to compiler object that has processed the XPath operations into an opcode map.

stepOpCodePos - The opcode position for the step.

stepIndex - The top-level step index withing the iterator.

analysis - The general analysis of the pattern.

Returns:

true if the walk can be done in natural order.

Throws:

javax.xml.transform.TransformerException

isOneStep

public static boolean isOneStep(int analysis)

getStepCount

public static int getStepCount(int analysis)