Class 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.
    • 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
      • 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.

        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Specified by:
        close in interface SequenceIterator
      • discharge

        public void discharge()
        Description copied from interface: SequenceIterator
        Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence. This may require the iterator to calculate the rest of the sequence eagerly. The method is called by a client if it anticipates that it might not read the iterator to completion, but it cannot guarantee that SequenceIterator.close() will be called when no more items are needed.
        Specified by:
        discharge in interface SequenceIterator