Package org.apache.accumulo.core.iterators

Class TypedValueCombiner<V>

  • All Implemented Interfaces:
    OptionDescriber, SortedKeyValueIterator<Key,​Value>, YieldingKeyValueIterator<Key,​Value>
    Direct Known Subclasses:
    BigDecimalCombiner, LongCombiner, SummingArrayCombiner
    public abstract class TypedValueCombiner<V>
extends Combiner
    A Combiner that decodes each Value to type V before reducing, then encodes the result of typedReduce back to Value. Subclasses must implement a typedReduce method: public V typedReduce(Key key, Iterator<V> iter); This typedReduce method will be passed the most recent Key and an iterator over the Values (translated to Vs) for all non-deleted versions of that Key. Subclasses may implement a switch on the "type" variable to choose an Encoder in their init method.

    • Constructor Detail

      • TypedValueCombiner

        public TypedValueCombiner()

    • Method Detail

      • setEncoder

        protected void setEncoder​(Encoder<V> encoder)
        Sets the Encoder<V> used to translate Values to V and back.

      • setEncoder

        protected void setEncoder​(String encoderClass)
        Instantiates and sets the Encoder<V> used to translate Values to V and back.
        Throws:
        IllegalArgumentException - if ClassNotFoundException, InstantiationException, or IllegalAccessException occurs

      • testEncoder

        protected void testEncoder​(V v)
        Tests whether v remains the same when encoded and decoded with the current encoder.
        Throws:
        IllegalStateException - if an encoder has not been set.
        IllegalArgumentException - if the test fails.

      • testEncoder

        public static <V> void testEncoder​(Encoder<V> encoder,
                                   V v)
        Tests whether v remains the same when encoded and decoded with the given encoder.
        Throws:
        IllegalArgumentException - if the test fails.

      • deepCopy

        public SortedKeyValueIterator<Key,​Value> deepCopy​(IteratorEnvironment env)
        Description copied from interface: SortedKeyValueIterator
        Creates a deep copy of this iterator as though seek had not yet been called. init should be called on an iterator before deepCopy is called. init should not need to be called on the copy that is returned by deepCopy; that is, when necessary init should be called in the deepCopy method on the iterator it returns. The behavior is unspecified if init is called after deepCopy either on the original or the copy. A proper implementation would call deepCopy on the source.
        Specified by:
        deepCopy in interface SortedKeyValueIterator<Key,​Value>
        Overrides:
        deepCopy in class Combiner
        Parameters:
        env - IteratorEnvironment environment in which iterator is being run.
        Returns:
        SortedKeyValueIterator a copy of this iterator (with the same source and settings).

      • reduce

        public Value reduce​(Key key,
                    Iterator<Value> iter)
        Description copied from class: Combiner
        Reduces a list of Values into a single Value.
        Specified by:
        reduce in class Combiner
        Parameters:
        key - The most recent version of the Key being reduced.
        iter - An iterator over the Values for different versions of the key.
        Returns:
        The combined Value.

      • validateOptions

        public boolean validateOptions​(Map<String,​String> options)
        Description copied from interface: OptionDescriber
        Check to see if an options map contains all options required by an iterator and that the option values are in the expected formats.
        Specified by:
        validateOptions in interface OptionDescriber
        Overrides:
        validateOptions in class Combiner
        Parameters:
        options - a map of option names to option values
        Returns:
        true if options are valid, false otherwise (IllegalArgumentException preferred)

      • setLossyness

        public static void setLossyness​(IteratorSetting is,
                                boolean lossy)
        A convenience method to set the "lossy" option on a TypedValueCombiner. If true, the combiner will ignore any values which fail to decode. Otherwise, the combiner will throw an error which will interrupt the action (and prevent potential data loss). False is the default behavior.
        Parameters:
        is - iterator settings object to configure
        lossy - if true the combiner will ignored values which fail to decode; otherwise error.

      • typedReduce

        public abstract V typedReduce​(Key key,
                              Iterator<V> iter)
        Reduces a list of V into a single V.
        Parameters:
        key - The most recent version of the Key being reduced.
        iter - An iterator over the V for different versions of the key.
        Returns:
        The combined V.