Flyweight

Intenção

Usar compartilhamento para apoiar eficientemente grandes quantidades de objetos de granularidade fina.

Vantagens

O gerenciamento do pool de objetos Request é centralizado no factory. Assim, se surgir uma nova subclasse concreta de Request, não é necessário garantir uma única instância nessa nova classe, pois isto já é feito no gerenciamento dentro do pool.
Simplicidade no gerenciamento das únicas instâncias.

Desvantagens

O gerenciamento do pool gera uma complexidade a mais na implementação.

Exemplos

Exemplo #1

Seja um processador de requisições (Request Processor) cuja responsabilidade é receber uma requisição e processá-la sobre a camada de objetos de negócio (Product, Customer) do domínio (domain model). Um objeto Request é criado para representar a requisição, encapsulando sua lógica de execução. Assim, para cada requisição, o correspondente objeto Request deve ser criado para executá-la. Como não é necessário armazenar o histórico de execução das requisições, é possível ter todos os objetos Request sem estado intrínseco específico da requisição, e compartilhar objetos Request entre requisições do mesmo tipo, diminuindo o overhead de criação e gerenciamento destes objetos, que podem ser muitos. Para tal, valores específicos da requisição precisam ser modelados como estado extrínseco do objeto Request, sendo passados como parâmetros. A classe RequestFactory contém um pool de gerenciamento de objetos Request. Esses objetos são criados sob demanda no primeiro acesso.

Diagrama de Classe

Participantes

Flyweight (Request)

Declara uma interface através da qual flyweights podem receber e atuar sobre estados extrínsecos.

ConcreteFlyweight (EditProductRequest, EditCustomerRequest)

Implementa a interface de Flyweight e acrescenta armazenamento para estados intrínsecos, se houver.

FlyweightFactory (RequestFactory)

Cria e gerencia objetos flyweights e garante que eles sejam compartilhados apropriadamente.

Client (RequestProcessor)

Mantém referências para os flyweights, neste caso, referências transientes durante o processamento das requisições.

Código

CommerceFlyweight/.classpath

CommerceFlyweight/.project



	CommerceFlyweight
	
	
	
	
		
			org.eclipse.jdt.core.javabuilder
			
			
		
	
	
		org.eclipse.jdt.core.javanature

CommerceFlyweight/.settings/

CommerceFlyweight/.settings/org.eclipse.jdt.core.prefs

eclipse.preferences.version=1
org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
org.eclipse.jdt.core.compiler.codegen.targetPlatform=11
org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
org.eclipse.jdt.core.compiler.compliance=11
org.eclipse.jdt.core.compiler.debug.lineNumber=generate
org.eclipse.jdt.core.compiler.debug.localVariable=generate
org.eclipse.jdt.core.compiler.debug.sourceFile=generate
org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
org.eclipse.jdt.core.compiler.problem.enablePreviewFeatures=disabled
org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
org.eclipse.jdt.core.compiler.problem.reportPreviewFeatures=warning
org.eclipse.jdt.core.compiler.release=enabled
org.eclipse.jdt.core.compiler.source=11

CommerceFlyweight/bin/br/uff/commerce/domain/customer/Customer.class

����71(br/uff/commerce/domain/customer/Customerjava/lang/ObjectidJnameLjava/lang/String;(JLjava/lang/String;)VCode

	()V	
setName(Ljava/lang/String;)VLineNumberTableLocalVariableTablethis*Lbr/uff/commerce/domain/customer/Customer;getId()JgetName()Ljava/lang/String;	
 "!java/lang/String#trim
 %&'isEmpty()Z)"java/lang/IllegalArgumentException+Name is mandatory.
(-	
StackMapTable
SourceFile
Customer.java!	
Y*�*�*-��
	 /*��/*��h+�
+��$�
�(Y*�,�*+��.	/0

CommerceFlyweight/bin/br/uff/commerce/domain/customer/CustomerRepository.class

����7"2br/uff/commerce/domain/customer/CustomerRepositoryjava/lang/ObjectsoleInstance4Lbr/uff/commerce/domain/customer/CustomerRepository;()VCode	LineNumberTableLocalVariableTablegetSoleInstance6()Lbr/uff/commerce/domain/customer/CustomerRepository;

StackMapTable
thisinsert-(Lbr/uff/commerce/domain/customer/Customer;)Vproduct*Lbr/uff/commerce/domain/customer/Customer;removeupdatefindById-(J)Lbr/uff/commerce/domain/customer/Customer;idJ
SourceFileCustomerRepository.java!
	%�
�

		E�
�
�Y��
�
�
	3*��

	5�
	5�!
	5�&
	6�+
 !

CommerceFlyweight/bin/br/uff/commerce/domain/customer/EditCustomerRequest.class

����7`3br/uff/commerce/domain/customer/EditCustomerRequestjava/lang/Objectbr/uff/commerce/request/RequestNAMELjava/lang/String;
ConstantValueeditCustomer()VCode

LineNumberTableLocalVariableTablethis5Lbr/uff/commerce/domain/customer/EditCustomerRequest;execute(Ljava/util/Map;)V
Exceptions(br/uff/commerce/request/RequestException	Signature8(Ljava/util/Map;)V
customerId! 
java/util/Map"#get&(Ljava/lang/Object;)Ljava/lang/Object;%java/lang/Long
')(2br/uff/commerce/domain/customer/CustomerRepository*+getSoleInstance6()Lbr/uff/commerce/domain/customer/CustomerRepository;
$-./	longValue()J
'123findById-(J)Lbr/uff/commerce/domain/customer/Customer;5java/lang/StringBuilder7Customer with id 
49:(Ljava/lang/String;)V
4<=>append-(Ljava/lang/Object;)Ljava/lang/StringBuilder;@ not found.
4B=C-(Ljava/lang/String;)Ljava/lang/StringBuilder;
4EFGtoString()Ljava/lang/String;
9JnameLjava/lang/String
NPO(br/uff/commerce/domain/customer/CustomerQ:setName
'STUupdate-(Lbr/uff/commerce/domain/customer/Customer;)V
parametersLjava/util/Map;Ljava/lang/Long;subject*Lbr/uff/commerce/domain/customer/Customer;LocalVariableTypeTable5Ljava/util/Map;
StackMapTable
SourceFileEditCustomerRequest.java!	

/*���O+��$M�&,�,�0N-� �Y�4Y6�8,�;?�A�D�H�-+I��K�M�&-�R�*
(48GN!*OOVWCX8YZ[OV\]�8$N^_

CommerceFlyweight/bin/br/uff/commerce/domain/product/EditProductRequest.class

����7`1br/uff/commerce/domain/product/EditProductRequestjava/lang/Objectbr/uff/commerce/request/RequestNAMELjava/lang/String;
ConstantValueeditProduct()VCode

LineNumberTableLocalVariableTablethis3Lbr/uff/commerce/domain/product/EditProductRequest;execute(Ljava/util/Map;)V
Exceptions(br/uff/commerce/request/RequestException	Signature8(Ljava/util/Map;)V	productId! 
java/util/Map"#get&(Ljava/lang/Object;)Ljava/lang/Object;%java/lang/Long
')(0br/uff/commerce/domain/product/ProductRepository*+getSoleInstance4()Lbr/uff/commerce/domain/product/ProductRepository;
$-./	longValue()J
'123findById+(J)Lbr/uff/commerce/domain/product/Product;5java/lang/StringBuilder7Product with id 
49:(Ljava/lang/String;)V
4<=>append-(Ljava/lang/Object;)Ljava/lang/StringBuilder;@ not found.
4B=C-(Ljava/lang/String;)Ljava/lang/StringBuilder;
4EFGtoString()Ljava/lang/String;
9JnameLjava/lang/String
NPO&br/uff/commerce/domain/product/ProductQ:setName
'STUupdate+(Lbr/uff/commerce/domain/product/Product;)V
parametersLjava/util/Map;Ljava/lang/Long;subject(Lbr/uff/commerce/domain/product/Product;LocalVariableTypeTable5Ljava/util/Map;
StackMapTable
SourceFileEditProductRequest.java!	

/*���O+��$M�&,�,�0N-� �Y�4Y6�8,�;?�A�D�H�-+I��K�M�&-�R�*
(48GN!*OOVWCX8YZ[OV\]�8$N^_

CommerceFlyweight/bin/br/uff/commerce/domain/product/Product.class

����71&br/uff/commerce/domain/product/Productjava/lang/ObjectidJnameLjava/lang/String;(JLjava/lang/String;)VCode

	()V	
setName(Ljava/lang/String;)VLineNumberTableLocalVariableTablethis(Lbr/uff/commerce/domain/product/Product;getId()JgetName()Ljava/lang/String;	
 "!java/lang/String#trim
 %&'isEmpty()Z)"java/lang/IllegalArgumentException+Name is mandatory.
(-	
StackMapTable
SourceFileProduct.java!	
Y*�*�*-��
	 /*��/*��h+�
+��$�
�(Y*�,�*+��.	/0

CommerceFlyweight/bin/br/uff/commerce/domain/product/ProductRepository.class

����7"0br/uff/commerce/domain/product/ProductRepositoryjava/lang/ObjectsoleInstance2Lbr/uff/commerce/domain/product/ProductRepository;()VCode	LineNumberTableLocalVariableTablegetSoleInstance4()Lbr/uff/commerce/domain/product/ProductRepository;

StackMapTable
thisinsert+(Lbr/uff/commerce/domain/product/Product;)Vproduct(Lbr/uff/commerce/domain/product/Product;removeupdatefindById+(J)Lbr/uff/commerce/domain/product/Product;idJ
SourceFileProductRepository.java!
	%�
�

		E�
�
�Y��
�
�
	3*��

	5�
	5�!
	5�&
	6�+
 !

CommerceFlyweight/bin/br/uff/commerce/request/Request.class

����7br/uff/commerce/request/Requestjava/lang/Objectexecute(Ljava/util/Map;)V
Exceptions	(br/uff/commerce/request/RequestException	Signature8(Ljava/util/Map;)V
SourceFileRequest.java

CommerceFlyweight/bin/br/uff/commerce/request/RequestException.class

����7(br/uff/commerce/request/RequestExceptionjava/lang/ExceptionserialVersionUIDJ
ConstantValue()VCode

LineNumberTableLocalVariableTablethis*Lbr/uff/commerce/request/RequestException;(Ljava/lang/String;)V

messageLjava/lang/String;
SourceFileRequestException.java!
3*�
�

>*+��

CommerceFlyweight/bin/br/uff/commerce/requestprocessing/RequestFactory.class

����7^0br/uff/commerce/requestprocessing/RequestFactoryjava/lang/ObjectsoleInstance2Lbr/uff/commerce/requestprocessing/RequestFactory;poolLjava/util/Map;	SignatureDLjava/util/Map;()VCode	LineNumberTableLocalVariableTablegetSoleInstance4()Lbr/uff/commerce/requestprocessing/RequestFactory;

StackMapTable
java/util/HashMap
	this
createRequest5(Ljava/lang/String;)Lbr/uff/commerce/request/Request;
"$#java/lang/String%&trim()Ljava/lang/String;
"()*isEmpty()Z,"java/lang/IllegalArgumentException.Request name is mandatory.
+01(Ljava/lang/String;)V354
java/util/Map67get&(Ljava/lang/Object;)Ljava/lang/Object;9br/uff/commerce/request/Request;editProduct
"=>?equals(Ljava/lang/Object;)ZA1br/uff/commerce/domain/product/EditProductRequest
@DeditCustomerF3br/uff/commerce/domain/customer/EditCustomerRequest
EIjava/lang/StringBuilderKRequest object not found for 
H0
HNOPappend-(Ljava/lang/String;)Ljava/lang/StringBuilder;
HRS&toString3UVWput8(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;requestNameLjava/lang/String;result!Lbr/uff/commerce/request/Request;
SourceFileRequestFactory.java!
	

%��	
E��
�Y����
B*�*�Y��� 
�x+�
+�!�'�
�+Y-�/�*�+�2�8M,�O+:�<��@Y�BM�/+C�<��EY�GM��+Y�HYJ�L+�M�Q�/�*�+,�TW,�6
#$&&(**3+>,G-R/V0f/j2v6 xxXY&RZ[
	�%8\]

CommerceFlyweight/bin/br/uff/commerce/requestprocessing/RequestProcessor.class

����7:2br/uff/commerce/requestprocessing/RequestProcessorjava/lang/ObjectsoleInstance4Lbr/uff/commerce/requestprocessing/RequestProcessor;factory2Lbr/uff/commerce/requestprocessing/RequestFactory;()VCode	
LineNumberTableLocalVariableTablegetSoleInstance6()Lbr/uff/commerce/requestprocessing/RequestProcessor;


StackMapTable

0br/uff/commerce/requestprocessing/RequestFactory4()Lbr/uff/commerce/requestprocessing/RequestFactory;	thisprocess$(Ljava/lang/String;Ljava/util/Map;)V
Exceptions#(br/uff/commerce/request/RequestException	SignatureJ(Ljava/lang/String;Ljava/util/Map;)V
'()
createRequest5(Ljava/lang/String;)Lbr/uff/commerce/request/Request;+-,br/uff/commerce/request/Request./execute(Ljava/util/Map;)VrequestNameLjava/lang/String;
parametersLjava/util/Map;request!Lbr/uff/commerce/request/Request;LocalVariableTypeTable5Ljava/util/Map;
SourceFileRequestProcessor.java!
	
%��	E��
�Y����
>*�*��� !"$%s*�+�&N-,�*�"	#$*0123	4562789

CommerceFlyweight/src/br/uff/commerce/domain/customer/Customer.java

package br.uff.commerce.domain.customer;

public class Customer
{
	private long id;
	private String name;
	
	public Customer(long id, String name)
	{
		this.id = id;
		this.setName(name);
	}
	
	public long getId()
	{
		return this.id;
	}
	
	public String getName()
	{
		return this.name;
	}
	
	public final void setName(String name)
	{
		if (name == null || name.trim().isEmpty())
			throw new IllegalArgumentException("Name is mandatory.");
		
		this.name = name;
	}	

}

CommerceFlyweight/src/br/uff/commerce/domain/customer/CustomerRepository.java

package br.uff.commerce.domain.customer;

/**
 * Reposit�rio (persist�ncia) de Cliente
 * Singleton
 *
 */
public class CustomerRepository
{
	private static CustomerRepository soleInstance = null;
	
	public static CustomerRepository getSoleInstance()
	{
		if (CustomerRepository.soleInstance == null)
			CustomerRepository.soleInstance = new CustomerRepository();
		
		return CustomerRepository.soleInstance;
	}
	
	private CustomerRepository()
	{
		
	}
	
	public void insert(Customer product)
	{
		//insere novo cliente
	}
	
	public void remove(Customer product)
	{
		//remove cliente
	}
	
	public void update(Customer product)
	{
	   //atualiza cliente	
	}
	
	public Customer findById(long id)
	{
		//busca e retorna cliente pelo respectivo id
		return null;
	}
}

CommerceFlyweight/src/br/uff/commerce/domain/customer/EditCustomerRequest.java

package br.uff.commerce.domain.customer;

import java.util.Map;

import br.uff.commerce.request.Request;
import br.uff.commerce.request.RequestException;

/**
 * Concrete Flyweight
 *
 */
public class EditCustomerRequest implements Request
{
	public final static String NAME = "editCustomer";

	@Override
	public void execute(Map parameters) throws RequestException
	{
		
		Long customerId = (Long) parameters.get("customerId");
		
		Customer subject = 
				CustomerRepository.getSoleInstance().findById(customerId);
		
		if (subject == null)
			throw new RequestException("Customer with id "+ 
		                                customerId +" not found.");
			
		subject.setName((String) parameters.get("name"));
		
		CustomerRepository.getSoleInstance().update(subject);
		
	}

}

CommerceFlyweight/src/br/uff/commerce/domain/product/EditProductRequest.java

package br.uff.commerce.domain.product;

import java.util.Map;

import br.uff.commerce.request.Request;
import br.uff.commerce.request.RequestException;

/**
 * Concrete Flyweight
 *
 */
public class EditProductRequest implements Request
{
	public final static String NAME = "editProduct";

	@Override
	public void execute(Map parameters) throws RequestException
	{
		
		Long productId = (Long) parameters.get("productId");
		
		Product subject = 
				ProductRepository.getSoleInstance().findById(productId);
		
		if (subject == null)
			throw new RequestException("Product with id "+ 
		                                productId +" not found.");
			
		subject.setName((String) parameters.get("name"));
		
		ProductRepository.getSoleInstance().update(subject);
		
	}

}

CommerceFlyweight/src/br/uff/commerce/domain/product/Product.java

package br.uff.commerce.domain.product;

public class Product
{
	private long id;
	private String name;
	
	public Product(long id, String name)
	{
		this.id = id;
		this.setName(name);
	}
	
	public long getId()
	{
		return this.id;
	}
	
	public String getName()
	{
		return this.name;
	}
	
	public final void setName(String name)
	{
		if (name == null || name.trim().isEmpty())
			throw new IllegalArgumentException("Name is mandatory.");
		
		this.name = name;
	}	

}

CommerceFlyweight/src/br/uff/commerce/domain/product/ProductRepository.java

package br.uff.commerce.domain.product;

/**
 * Reposit�rio (persist�ncia) de Produto
 * Singleton
 *
 */
public class ProductRepository
{
	private static ProductRepository soleInstance = null;
	
	public static ProductRepository getSoleInstance()
	{
		if (ProductRepository.soleInstance == null)
			ProductRepository.soleInstance = new ProductRepository();
		
		return ProductRepository.soleInstance;
	}
	
	private ProductRepository()
	{
		
	}
	
	public void insert(Product product)
	{
		//insere novo produto
	}
	
	public void remove(Product product)
	{
		//remove produto
	}
	
	public void update(Product product)
	{
	   //atualiza produto	
	}
	
	public Product findById(long id)
	{
		//busca e retorna produto pelo respectivo id
		return null;
	}
}

CommerceFlyweight/src/br/uff/commerce/request/Request.java

package br.uff.commerce.request;

import java.util.Map;

/**
 * Flyweight
 *
 */
public interface Request
{
	public void execute(Map parameters) throws RequestException;
}

CommerceFlyweight/src/br/uff/commerce/request/RequestException.java

package br.uff.commerce.request;

/**
 * Indica algum problema na execu��o de uma requisi��o.
 *
 */
public class RequestException extends Exception
{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	public RequestException()
	{
		super();
		
	}

	public RequestException(String message)
	{
		super(message);
		
	}

}

CommerceFlyweight/src/br/uff/commerce/requestprocessing/RequestFactory.java

package br.uff.commerce.requestprocessing;

import java.util.HashMap;
import java.util.Map;

import br.uff.commerce.domain.customer.EditCustomerRequest;
import br.uff.commerce.domain.product.EditProductRequest;
import br.uff.commerce.request.Request;

/**
 * Factory parametrizado e Singleton.
 *
 */
public class RequestFactory
{
	private static RequestFactory soleInstance = null;
	
	public static RequestFactory getSoleInstance()
	{
		if (RequestFactory.soleInstance == null)
			RequestFactory.soleInstance = new RequestFactory();
		
		return RequestFactory.soleInstance;
	}
	
	private Map pool;
	
	private RequestFactory() 
	{
		this.pool = new HashMap();
	}
	
	public Request createRequest(String requestName)
	{
		if (requestName == null || requestName.trim().isEmpty())
			throw new IllegalArgumentException("Request name is mandatory.");
		
		Request result = this.pool.get(requestName);
		
		if (result == null)
		{
			if (requestName.equals(EditProductRequest.NAME))
				result = new EditProductRequest();
			else if (requestName.equals(EditCustomerRequest.NAME))
				result = new EditCustomerRequest();
			else 
				throw new IllegalArgumentException(
						"Request object not found for "+ requestName);
			
			this.pool.put(requestName, result);
			
		}
		
		return result;
	}
	
}

CommerceFlyweight/src/br/uff/commerce/requestprocessing/RequestProcessor.java

package br.uff.commerce.requestprocessing;

import java.util.Map;

import br.uff.commerce.request.Request;
import br.uff.commerce.request.RequestException;

/**
 * Singleton
 *
 */
public class RequestProcessor
{
	private static RequestProcessor soleInstance = null;
	
	public static RequestProcessor getSoleInstance()
	{
		if (RequestProcessor.soleInstance == null)
			RequestProcessor.soleInstance = new RequestProcessor();
		
		return RequestProcessor.soleInstance;
	}
	
	private RequestFactory factory;
	
	private RequestProcessor()
	{
		this.factory = RequestFactory.getSoleInstance();
	}
	
	public void process(String requestName, Map parameters) 
			throws RequestException
	{
		Request request = this.factory.createRequest(requestName);
		request.execute(parameters);
	}
	
}

Clique aqui para fazer o download do código completo de implementação deste Design Pattern.

Padrões Relacionados

Este Padrão pode ser usado para resolver os seguintes problemas:

Como reutilizar instâncias para diminuir o overhead na criação ou gerenciamento de objetos?