IN
- Type of objects to extract the key from.KEY
- Type of key.@Public @FunctionalInterface public interface KeySelector<IN,KEY> extends Function, Serializable
KeySelector
allows to use deterministic objects for operations such as
reduce, reduceGroup, join, coGroup, etc. If invoked multiple times on the same object,
the returned key must be the same.
The extractor takes an object and returns the deterministic key for that object.
Modifier and Type | Method and Description |
---|---|
KEY |
getKey(IN value)
User-defined function that deterministically extracts the key from an object.
|
KEY getKey(IN value) throws Exception
For example for a class:
public class Word { String word; int count; }The key extractor could return the word as a key to group all Word objects by the String they contain.
The code would look like this
public String getKey(Word w) { return w.word; }
value
- The object to get the key from.Exception
- Throwing an exception will cause the execution of the respective task to fail,
and trigger recovery or cancellation of the program.Copyright © 2014–2020 The Apache Software Foundation. All rights reserved.