org.apache.nifi.attribute.expression.language.evaluation

Class EvaluatorState

java.lang.Object

org.apache.nifi.attribute.expression.language.evaluation.EvaluatorState

public class EvaluatorState
extends Object

A storage mechanism for Evaluators to stash & retrieve state. While most Evaluators are stateless, some must maintain state, for instance to iterate over many Attributes. By stashing that state and retrieving it from this EvaluatorState instead of using member variables, Evaluators are able to be kept both threadsafe and in-and-of-themselves stateless, which means that new Evaluators need not be created for each iteration of the function.

Field Summary

Fields

Modifier and Type	Field and Description
private Map<Evaluator<?>,Object>	statePerEvaluator

Constructor Summary

Constructors

Constructor and Description
EvaluatorState()

Method Summary

Modifier and Type	Method and Description
<T> T	getState(Evaluator<?> evaluator, Class<T> clazz) Fetches state for the given evaluator, casting it into the given type
void	putState(Evaluator<?> evaluator, Object state) Updates state for the given Evaluator

Methods inherited from class java.lang.Object

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

Field Detail

statePerEvaluator

private final Map<Evaluator<?>,Object> statePerEvaluator

Constructor Detail

EvaluatorState

public EvaluatorState()

Method Detail

getState

public <T> T getState(Evaluator<?> evaluator,
                      Class<T> clazz)

Fetches state for the given evaluator, casting it into the given type

Type Parameters:

T - type Type of the value

Parameters:

evaluator - the Evaluator to retrieve state for

clazz - the Class to which the value should be cast

Returns:

the state for the given Evaluator, or null if no state has been stored

putState

public void putState(Evaluator<?> evaluator,
                     Object state)

Updates state for the given Evaluator

Parameters:

evaluator - the Evaluator to store state for

state - the state to store