Package net.sf.saxon.expr

Class ItemMappingIterator

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, LastPositionFinder, SequenceIterator, LookaheadIterator
    Direct Known Subclasses:
    MultithreadedItemMappingIterator
    public class ItemMappingIterator
extends java.lang.Object
implements SequenceIterator, LookaheadIterator, LastPositionFinder
    ItemMappingIterator applies a mapping function to each item in a sequence. The mapping function either returns a single item, or null (representing an empty sequence).

    This is a specialization of the more general MappingIterator class, for use in cases where a single input item never maps to a sequence of more than one output item.

    The Java implementation accepts a lambda expression as the mapping function (because it is a functional interface, even though not declared as such). To achieve the same effect on C# we add extra constructors that explicitly accept a lambda expression, by virtue of the fact that the expected type is a functional interface (which translates to a C# delegate)

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void close()
      Close the iterator.
      void discharge()
      Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence.
      static ItemMappingIterator filter​(SequenceIterator base, ItemFilter.Lambda filterExpression)
      Factory method designed for use when the mapping function is designed to filter the input nodes Example of usage: ItemMappingIterator.filter(base, item -> item.hasChildNodes())
      protected SequenceIterator getBaseIterator()
      Get the base (input) iterator
      int getLength()
      Get the last position (that is, the number of items in the sequence).
      protected ItemMappingFunction getMappingFunction()
      Get the mapping function (the function applied to each item in the input sequence
      boolean hasNext()
      Determine whether there are more items to come.
      boolean isOneToOne()
      Ask whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item.
      static ItemMappingIterator map​(SequenceIterator base, ItemMapper.Lambda mappingExpression)
      Factory method designed for use when the mapping function is a lambda expression Example of usage: ItemMappingIterator.map(base, item -> item.getParentNode())
      Item next()
      Get the next item in the sequence.
      void setOneToOne​(boolean oneToOne)
      Say whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item.
      boolean supportsGetLength()
      Ask whether this iterator supports use of the LastPositionFinder.getLength() method.
      boolean supportsHasNext()
      Ask whether the hasNext() method can be called.

      • Methods inherited from class java.lang.Object

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

    • Constructor Detail

      • ItemMappingIterator

        public ItemMappingIterator​(SequenceIterator base,
                           ItemMappingFunction action)
        Construct an ItemMappingIterator that will apply a specified ItemMappingFunction to each Item returned by the base iterator.
        Parameters:
        base - the base iterator
        action - the mapping function to be applied.

      • ItemMappingIterator

        public ItemMappingIterator​(SequenceIterator base,
                           ItemMappingFunction action,
                           boolean oneToOne)
        Construct an ItemMappingIterator that will apply a specified ItemMappingFunction to each Item returned by the base iterator.
        Parameters:
        base - the base iterator
        action - the mapping function to be applied
        oneToOne - true if this iterator is one-to-one

    • Method Detail

      • map

        public static ItemMappingIterator map​(SequenceIterator base,
                                      ItemMapper.Lambda mappingExpression)
        Factory method designed for use when the mapping function is a lambda expression Example of usage: ItemMappingIterator.map(base, item -> item.getParentNode())
        Parameters:
        base - iterator over the base sequence
        mappingExpression - function to be applied to items in the base sequence
        Returns:
        an iterator over the items determined by applying the mapping expression to every item in the base sequence (a flatMap operation).

      • filter

        public static ItemMappingIterator filter​(SequenceIterator base,
                                         ItemFilter.Lambda filterExpression)
        Factory method designed for use when the mapping function is designed to filter the input nodes Example of usage: ItemMappingIterator.filter(base, item -> item.hasChildNodes())
        Parameters:
        base - iterator over the base sequence
        filterExpression - predicate to be applied to items in the base sequence
        Returns:
        an iterator over the items in the base sequence that satisfy the predicate

      • setOneToOne

        public void setOneToOne​(boolean oneToOne)
        Say whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item. The default is false.
        Parameters:
        oneToOne - true if this iterator is one-to-one

      • isOneToOne

        public boolean isOneToOne()
        Ask whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item. The default is false.
        Returns:
        true if this iterator is one-to-one

      • getBaseIterator

        protected SequenceIterator getBaseIterator()
        Get the base (input) iterator
        Returns:
        the iterator over the input sequence

      • getMappingFunction

        protected ItemMappingFunction getMappingFunction()
        Get the mapping function (the function applied to each item in the input sequence
        Returns:
        the mapping function

      • supportsHasNext

        public boolean supportsHasNext()
        Description copied from interface: LookaheadIterator
        Ask whether the hasNext() method can be called. This method must be called before calling hasNext(), because some iterators implement this interface, but only support look-ahead under particular circumstances (this is usually because they delegate to another iterator)
        Specified by:
        supportsHasNext in interface LookaheadIterator
        Returns:
        true if the LookaheadIterator.hasNext() method is available

      • hasNext

        public boolean hasNext()
        Description copied from interface: LookaheadIterator
        Determine whether there are more items to come. Note that this operation is stateless and it is not necessary (or usual) to call it before calling next(). It is used only when there is an explicit need to tell if we are at the last element.

        This method must not be called unless the result of LookaheadIterator.supportsHasNext() is true.

        Specified by:
        hasNext in interface LookaheadIterator
        Returns:
        true if there are more items in the sequence

      • next

        public Item next()
        Description copied from interface: SequenceIterator
        Get the next item in the sequence. This method changes the state of the iterator.
        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.

      • 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

      • getLength

        public int getLength()
        Description copied from interface: LastPositionFinder
        Get the last position (that is, the number of items in the sequence). This method is non-destructive: it does not change the state of the iterator. The result is undefined if the next() method of the iterator has already returned null. This method must not be called unless the LastPositionFinder.supportsGetLength() has been called and has returned true.
        Specified by:
        getLength in interface LastPositionFinder
        Returns:
        the number of items in the sequence