com.hazelcast.query.extractor

Class ValueExtractor<T,R>

java.lang.Object

com.hazelcast.query.extractor.ValueExtractor<T,R>

Type Parameters:

T - type of the target object to extract the value from

R - type of the result object - the extracted value

public abstract class ValueExtractor<T,R>
extends Object

Common superclass for all extractors that enable the user to define custom attributes and extract their values. The extraction logic may just extract the underlying value or group, reduce or transform it.

How to use a ValueExtractor?

First, extend this class and implement the @see com.hazelcast.query.extractor.ValueExtractor#extract method. Then, define a new attribute with the above-mentioned extractor in the configuration of the map.

How to define a new custom attribute? MapAttributeConfig attributeConfig = new MapAttributeConfig(); extractorConfig.setName("currency"); extractorConfig.setExtractor("com.bank.CurrencyExtractor");

How to register the newly-defined attribute in a configuration of a Map? MapConfig mapConfig = (...); mapConfig.addMapAttributeConfig(attributeConfig); Extractors may be also defined in the XML configuration.

Please, bear in mind that an extractor may not be added after the map has been instantiated. All extractor have to be defined upfront in the map's initial configuration.

Reflection-based extraction is the default mechanism - ValueExtractors are an alternative way of getting values from objects.

See Also:

MultiResult

Constructor Summary

Constructors

Constructor and Description
ValueExtractor()

Method Summary

Methods

Modifier and Type	Method and Description
protected MultiResult<R>	createMultiResult() Factory method for the MultiResult
abstract R	extract(T target) Extracts a value from the given target object.

Methods inherited from class java.lang.Object

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

Constructor Detail

ValueExtractor

public ValueExtractor()

Method Detail

extract

public abstract R extract(T target)

Extracts a value from the given target object.

May return:

• a single 'single-value' result (not a collection)
• a single 'multi-value' result (a collection)
• multiple 'single-value' or 'multi-value' results encompassed in a MultiResult

MultiResult is an aggregate of results that is returned if the extractor returns multiple results due to a reduce operation executed on a hierarchy of values.

Parameters:

target - object to extract the value from

Returns:

extracted value

See Also:

MultiResult

createMultiResult

protected MultiResult<R> createMultiResult()

Factory method for the MultiResult

Returns:

a new instance of the MultiResult class

See Also:

MultiResult