- All Implemented Interfaces:
- Direct Known Subclasses:
public class FilterIterator extends java.lang.Object implements SequenceIteratorA 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
FilterIterator.NonNumericSubclass to handle the common special case where it is statically known that the filter cannot return a numeric value
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description
close()Close the iterator.
getNextMatchingItem()Get the next item in the base sequence that matches the filter predicate if there is such an item, or null if not.
matches()Determine whether the context item matches the filter predicate
next()Get the next item if there is one
setSequence(SequenceIterator base, XPathContext context)Set the base iterator
testPredicateValue(SequenceIterator iterator, long position, Expression filter)
public void setSequence(SequenceIterator base, XPathContext context)Set the base iterator
base- the iterator over the sequence to be filtered
context- the context in which the (outer) filter expression is evaluated
public Item next()Get the next item if there is one
- Specified by:
- 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.
protected Item getNextMatchingItem() throws XPathExceptionGet the next item in the base sequence that matches the filter predicate if there is such an item, or null if not.
- the next item that matches the predicate
XPathException- if a dynamic error occurs
protected boolean matches() throws XPathExceptionDetermine whether the context item matches the filter predicate
- true if the context item matches
XPathException- if an error occurs evaluating the match
public static boolean testPredicateValue(SequenceIterator iterator, long position, Expression filter) throws XPathException
public void close()Description copied from interface:
SequenceIteratorClose 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
$varis passed to a user-written function, the function may access
$varonly; we have no way of knowing whether further items will be read. For this reason, any
SequenceIteratorthat holds resources which need to be closed should use the
Cleaner, and resources held by a
SequenceIteratorshould be registered with the
Cleaner; if the
SequenceIteratoris then garbage-collected without being closed, the
Cleanerwill ensure that the underlying resources are closed. (An example of a
SequenceIteratorthat uses this mechanism is the