Class FilterIterator

  • All Implemented Interfaces:, java.lang.AutoCloseable, SequenceIterator

    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.
    • Constructor Detail

      • FilterIterator

        public FilterIterator​(SequenceIterator base,
                              Expression filter,
                              XPathContext context)
        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
        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
        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.
        the next item that matches the predicate
        XPathException - if a dynamic error occurs
      • matches

        protected boolean matches()
                           throws XPathException
        Determine whether the context item matches the filter predicate
        true if the context item matches
        XPathException - if an error occurs evaluating the match
      • 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 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
        Specified by:
        close in interface SequenceIterator