org.apache.accumulo.core.iterators
Class TypedValueCombiner<V>

java.lang.Object
  extended by org.apache.accumulo.core.iterators.WrappingIterator
      extended by org.apache.accumulo.core.iterators.Combiner
          extended by org.apache.accumulo.core.iterators.TypedValueCombiner<V>
All Implemented Interfaces:
OptionDescriber, SortedKeyValueIterator<Key,Value>
Direct Known Subclasses:
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 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.


Nested Class Summary
static interface TypedValueCombiner.Encoder<V>
          An interface for translating from byte[] to V and back.
 
Nested classes/interfaces inherited from class org.apache.accumulo.core.iterators.Combiner
Combiner.ValueIterator
 
Nested classes/interfaces inherited from interface org.apache.accumulo.core.iterators.OptionDescriber
OptionDescriber.IteratorOptions
 
Field Summary
protected static String LOSSY
           
 
Fields inherited from class org.apache.accumulo.core.iterators.Combiner
ALL_OPTION, COLUMNS_OPTION
 
Constructor Summary
TypedValueCombiner()
           
 
Method Summary
 SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)
          Creates a deep copy of this iterator as though seek had not yet been called.
 OptionDescriber.IteratorOptions describeOptions()
          Gets an iterator options object that contains information needed to configure this iterator.
 void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env)
          Initializes the iterator.
 Value reduce(Key key, Iterator<Value> iter)
          Reduces a list of Values into a single Value.
protected  void setEncoder(String encoderClass)
          Instantiates and sets the Encoder used to translate Values to V and back.
protected  void setEncoder(TypedValueCombiner.Encoder<V> encoder)
          Sets the Encoder used to translate Values to V and back.
static void setLossyness(IteratorSetting is, boolean lossy)
          A convenience method to set the "lossy" option on a TypedValueCombiner.
static
<V> void
testEncoder(TypedValueCombiner.Encoder<V> encoder, V v)
          Tests whether v remains the same when encoded and decoded with the given encoder.
protected  void testEncoder(V v)
          Tests whether v remains the same when encoded and decoded with the current encoder.
abstract  V typedReduce(Key key, Iterator<V> iter)
          Reduces a list of V into a single V.
 boolean validateOptions(Map<String,String> options)
          Check to see if an options map contains all options required by an iterator and that the option values are in the expected formats.
 
Methods inherited from class org.apache.accumulo.core.iterators.Combiner
getTopKey, getTopValue, hasTop, next, seek, setColumns, setCombineAllColumns
 
Methods inherited from class org.apache.accumulo.core.iterators.WrappingIterator
getSource, setSource
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

LOSSY

protected static final String LOSSY
See Also:
Constant Field Values
Constructor Detail

TypedValueCombiner

public TypedValueCombiner()
Method Detail

setEncoder

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

Parameters:
encoder -

setEncoder

protected void setEncoder(String encoderClass)
Instantiates and sets the Encoder used to translate Values to V and back.

Parameters:
encoderClass -
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.

Parameters:
v -
Throws:
IllegalStateException - if an encoder has not been set.
IllegalArgumentException - if the test fails.

testEncoder

public static <V> void testEncoder(TypedValueCombiner.Encoder<V> encoder,
                                   V v)
Tests whether v remains the same when encoded and decoded with the given encoder.

Parameters:
encoder -
v -
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.

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.

init

public void init(SortedKeyValueIterator<Key,Value> source,
                 Map<String,String> options,
                 IteratorEnvironment env)
          throws IOException
Description copied from interface: SortedKeyValueIterator
Initializes the iterator. Data should not be read from the source in this method.

Specified by:
init in interface SortedKeyValueIterator<Key,Value>
Overrides:
init in class Combiner
Parameters:
source - SortedKeyValueIterator source to read data from.
options - Map map of string option names to option values.
env - IteratorEnvironment environment in which iterator is being run.
Throws:
IOException - unused.

describeOptions

public OptionDescriber.IteratorOptions describeOptions()
Description copied from interface: OptionDescriber
Gets an iterator options object that contains information needed to configure this iterator. This object will be used by the accumulo shell to prompt the user to input the appropriate information.

Specified by:
describeOptions in interface OptionDescriber
Overrides:
describeOptions in class Combiner
Returns:
an iterator options object

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.


Copyright © 2013 Apache Accumulo Project. All Rights Reserved.