Package net.sf.saxon.expr

Class FilterIterator

java.lang.Object

net.sf.saxon.expr.FilterIterator

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, SequenceIterator

Direct Known Subclasses:

FilterIterator.NonNumeric

public class FilterIterator
extends java.lang.Object
implements SequenceIterator

A FilterIterator filters an input sequence using a filter expression. Note that a FilterIterator is not used where the filter is a constant number (PositionFilter is used for this purpose instead), so this class does no optimizations for numeric predicates.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	FilterIterator.NonNumeric	Subclass to handle the common special case where it is statically known that the filter cannot return a numeric value

Field Summary

Fields

Modifier and Type	Field	Description
protected FocusIterator	base
protected Expression	filter
protected XPathContext	filterContext

Constructor Summary

Constructors

Constructor	Description
FilterIterator(SequenceIterator base, Expression filter, XPathContext context)	Constructor

Method Summary

Modifier and Type	Method	Description
void	close()	Close the iterator.
protected Item	getNextMatchingItem()	Get the next item in the base sequence that matches the filter predicate if there is such an item, or null if not.
protected boolean	matches()	Determine whether the context item matches the filter predicate
Item	next()	Get the next item if there is one
void	setSequence(SequenceIterator base, XPathContext context)	Set the base iterator
static boolean	testPredicateValue(SequenceIterator iterator, long position, Expression filter)

Methods inherited from class java.lang.Object

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

Field Detail

base

protected FocusIterator base

filter

protected Expression filter

filterContext

protected XPathContext filterContext

Constructor Detail

FilterIterator

public FilterIterator(SequenceIterator base,
                      Expression filter,
                      XPathContext context)

Constructor

Parameters:

base - An iteration of the items to be filtered

filter - The expression defining the filter predicate

context - The context in which the expression is being evaluated

Method Detail

setSequence

public void setSequence(SequenceIterator base,
                        XPathContext context)

Set the base iterator

Parameters:

base - the iterator over the sequence to be filtered

context - the context in which the (outer) filter expression is evaluated

next

public Item next()

Get the next item if there is one

Specified by:

next in interface SequenceIterator

Returns:

the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.

getNextMatchingItem

protected Item getNextMatchingItem()
                            throws XPathException

Get the next item in the base sequence that matches the filter predicate if there is such an item, or null if not.

Returns:

the next item that matches the predicate

Throws:

XPathException - if a dynamic error occurs

matches

protected boolean matches()
                   throws XPathException

Determine whether the context item matches the filter predicate

Returns:

true if the context item matches

Throws:

XPathException - if an error occurs evaluating the match

testPredicateValue

public static boolean testPredicateValue(SequenceIterator iterator,
                                         long position,
                                         Expression filter)
                                  throws XPathException

Throws:

XPathException

close

public void close()

Description copied from interface: SequenceIterator

Close the iterator. This indicates to the supplier of the data that the client does not require any more items to be delivered by the iterator. This may enable the supplier to release resources. After calling close(), no further calls on the iterator should be made; if further calls are made, the effect of such calls is undefined.

For example, the iterator returned by the unparsed-text-lines() function has a close() method that causes the underlying input stream to be closed, whether or not the file has been read to completion.

Closing an iterator is important when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.

Closing an iterator is not necessary if the iterator is read to completion: if a call on SequenceIterator.next() returns null, the iterator will be closed automatically. An explicit call on SequenceIterator.close() is needed only when iteration is abandoned prematurely.

It is not possible to guarantee that an iterator that is not read to completion or will be closed. For example, if a lazy-evaluated variable $var is passed to a user-written function, the function may access $var[1] only; we have no way of knowing whether further items will be read. For this reason, any SequenceIterator that holds resources which need to be closed should use the Cleaner mechanism. The Configuration holds a Cleaner, and resources held by a SequenceIterator should be registered with the Cleaner; if the SequenceIterator is then garbage-collected without being closed, the Cleaner will ensure that the underlying resources are closed. (An example of a SequenceIterator that uses this mechanism is the UnparsedTextIterator).

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface SequenceIterator