Facade Pattern
The Facade Pattern is used to consolidate numerous complicated objects and function calls in a single interface. It does not necessarily encapsulate the objects behind the facade, as it commonly allows the client to work directly with the object.
UML Example
Code Examples
Java
C++
C# .NET
Design Pattern in C# (via Data & Object Factory)]
// Facade pattern -- Structural example
using System;
namespace DoFactory.GangOfFour.Facade.Structural
{
// Mainapp test application
class MainApp
{
public static void Main()
{
Facade facade = new Facade();
facade.MethodA();
facade.MethodB();
// Wait for user
Console.Read();
}
}
// "Subsystem ClassA"
class SubSystemOne
{
public void MethodOne()
{
Console.WriteLine(" SubSystemOne Method");
}
}
// Subsystem ClassB"
class SubSystemTwo
{
public void MethodTwo()
{
Console.WriteLine(" SubSystemTwo Method");
}
}
// Subsystem ClassC"
class SubSystemThree
{
public void MethodThree()
{
Console.WriteLine(" SubSystemThree Method");
}
}
// Subsystem ClassD"
class SubSystemFour
{
public void MethodFour()
{
Console.WriteLine(" SubSystemFour Method");
}
}
// "Facade"
class Facade
{
SubSystemOne one;
SubSystemTwo two;
SubSystemThree three;
SubSystemFour four;
public Facade()
{
one = new SubSystemOne();
two = new SubSystemTwo();
three = new SubSystemThree();
four = new SubSystemFour();
}
public void MethodA()
{
Console.WriteLine("\nMethodA() ---- ");
one.MethodOne();
two.MethodTwo();
four.MethodFour();
}
public void MethodB()
{
Console.WriteLine("\nMethodB() ---- ");
two.MethodTwo();
three.MethodThree();
}
}
}
Open Source Applications
Apache Excalibur
Excalibur Facade Class Code (via Google! Code Search)
/**
* A facade to the modularized *LoggerManager building system.
* Add methods here to create LoggerManagers to your preference.
*
* @author <a href="mailto:dev@nospamavalon.apache.org">Avalon Development Team</a>
* @version CVS $Revision: 1.3 $ $Date: 2004/03/10 13:54:50 $
* @since 4.0
*/
public class Facade
{
/**
* Assemble a new LoggerManager running on top of LogKit
* configured from a configuration file logging to a supplied
* logger as a fallback.
* Use this method as a sample showing how to assemble your
* own LoggerManager running on top of LogKit flavour.
*/
public static LoggerManager createLogKitConfigurable(
final String prefix, final String switchTo )
{
final org.apache.log.Hierarchy hierarchy = new Hierarchy();
final LoggerManager bare = new LogKitAdapter( hierarchy );
final LoggerManager decorated = applyDecorators( bare, prefix, switchTo );
final LoggerManagerTee tee = new LoggerManagerTee( decorated );
tee.addTee( new LogKitLoggerHelper( hierarchy ) );
tee.addTee( new LogKitConfHelper( hierarchy ) );
tee.makeReadOnly();
return tee;
}
/**
* Assemble LoggerManager for Log4J system configured
* via a configuration file. All the logging errors
* will go to System.err however.
*/
public static LoggerManager createLog4JConfigurable(
final String prefix, final String switchTo )
{
final LoggerManager bare = new Log4JConfAdapter();
final LoggerManager decorated = applyDecorators( bare, prefix, switchTo );
return decorated;
}
private static LoggerManager applyDecorators( LoggerManager target,
final String prefix, final String switchTo )
{
if ( switchTo != null )
{
target = new LogToSelfDecorator( target, switchTo );
}
if ( prefix != null && prefix.length() > 0 )
{
target = new PrefixDecorator( target, prefix );
}
target = new CachingDecorator( target );
return target;
}
}
Apache Tomcat
Excalibur Facade Class Code (via Google! Code Search)/*
* Copyright 1999-2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*/
package org.apache.coyote.tomcat4;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Map;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletInputStream;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import org.apache.catalina.connector.RequestFacade;
/**
* Facade class that wraps a Coyote request object.
* All methods are delegated to the wrapped request.
*
* @author Craig R. McClanahan
* @author Remy Maucherat
* @version $Revision: 299222 $ $Date: 2004-02-24 04:02:18 -0500 (Tue, 24 Feb 2004) $
*/
public class CoyoteRequestFacade
extends RequestFacade
implements HttpServletRequest {
// ----------------------------------------------------------- Constructors
/**
* Construct a wrapper for the specified request.
* @param request The request to be wrapped
*/
public CoyoteRequestFacade(CoyoteRequest request) {
super(request);
this.request = request;
}
// ----------------------------------------------------- Instance Variables
/**
* The wrapped request.
*/
protected CoyoteRequest request = null;
// --------------------------------------------------------- Public Methods
/**
* Clear facade.
*/
public void clear() {
request = null;
}
// ------------------------------------------------- ServletRequest Methods
public Object getAttribute(String name) {
return request.getAttribute(name);
}
public Enumeration getAttributeNames() {
return request.getAttributeNames();
}
public String getCharacterEncoding() {
return request.getCharacterEncoding();
}
public void setCharacterEncoding(String env)
throws java.io.UnsupportedEncodingException {
request.setCharacterEncoding(env);
}
public int getContentLength() {
return request.getContentLength();
}
public String getContentType() {
return request.getContentType();
}
public ServletInputStream getInputStream()
throws IOException {
return request.getInputStream();
}
public String getParameter(String name) {
return request.getParameter(name);
}
public Enumeration getParameterNames() {
return request.getParameterNames();
}
public String[] getParameterValues(String name) {
return request.getParameterValues(name);
}
public Map getParameterMap() {
return request.getParameterMap();
}
public String getProtocol() {
return request.getProtocol();
}
public String getScheme() {
return request.getScheme();
}
public String getServerName() {
return request.getServerName();
}
public int getServerPort() {
return request.getServerPort();
}
public BufferedReader getReader()
throws IOException {
return request.getReader();
}
public String getRemoteAddr() {
return request.getRemoteAddr();
}
public String getRemoteHost() {
return request.getRemoteHost();
}
public void setAttribute(String name, Object o) {
request.setAttribute(name, o);
}
public void removeAttribute(String name) {
request.removeAttribute(name);
}
public Locale getLocale() {
return request.getLocale();
}
public Enumeration getLocales() {
return request.getLocales();
}
public boolean isSecure() {
return request.isSecure();
}
public RequestDispatcher getRequestDispatcher(String path) {
// TODO : Facade !!
return request.getRequestDispatcher(path);
}
public String getRealPath(String path) {
return request.getRealPath(path);
}
public String getAuthType() {
return request.getAuthType();
}
public Cookie[] getCookies() {
return request.getCookies();
}
public long getDateHeader(String name) {
return request.getDateHeader(name);
}
public String getHeader(String name) {
return request.getHeader(name);
}
public Enumeration getHeaders(String name) {
return request.getHeaders(name);
}
public Enumeration getHeaderNames() {
return request.getHeaderNames();
}
public int getIntHeader(String name) {
return request.getIntHeader(name);
}
public String getMethod() {
return request.getMethod();
}
public String getPathInfo() {
return request.getPathInfo();
}
public String getPathTranslated() {
return request.getPathTranslated();
}
public String getContextPath() {
return request.getContextPath();
}
public String getQueryString() {
return request.getQueryString();
}
public String getRemoteUser() {
return request.getRemoteUser();
}
public boolean isUserInRole(String role) {
return request.isUserInRole(role);
}
public java.security.Principal getUserPrincipal() {
return request.getUserPrincipal();
}
public String getRequestedSessionId() {
return request.getRequestedSessionId();
}
public String getRequestURI() {
return request.getRequestURI();
}
public StringBuffer getRequestURL() {
return request.getRequestURL();
}
public String getServletPath() {
return request.getServletPath();
}
public HttpSession getSession(boolean create) {
return request.getSession(create);
}
public HttpSession getSession() {
return getSession(true);
}
public boolean isRequestedSessionIdValid() {
return request.isRequestedSessionIdValid();
}
public boolean isRequestedSessionIdFromCookie() {
return request.isRequestedSessionIdFromCookie();
}
public boolean isRequestedSessionIdFromURL() {
return request.isRequestedSessionIdFromURL();
}
public boolean isRequestedSessionIdFromUrl() {
return request.isRequestedSessionIdFromURL();
}
}