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복잡한 과정을 간단하게 제공

Intent

Facade is a structural design pattern that provides a simplified interface to a library, a framework, or any other complex set of classes.

Implementation

Applicablity

복잡한 Subsystem의 인터페이스를 제한하고 싶을때

Subsystem을 계층 구조로 나타내고 싶을때

Examples

javax.faces.context.ExternalContext uses ServletContext, HttpSession, HttpServletRequest, HttpServletResponse and others inside.

Code Exampl


package oodesign.design.structural.facade.subsystem;

class HelpSystem01 {

    public HelpSystem01(){
        System.out.println("call constructor: "+getClass().getSimpleName());
    }

    public void proc(){
        System.out.println("call proc: "+getClass().getSimpleName());
    }
}

class HelpSystem02 {

    public HelpSystem02(){
        System.out.println("call constructor: "+getClass().getSimpleName());
    }

    public void proc(){
        System.out.println("call proc: "+getClass().getSimpleName());
    }
}

class HelpSystem03 {

    public HelpSystem03(){
        System.out.println("call constructor: "+getClass().getSimpleName());
    }

    public void proc(){
        System.out.println("call proc: "+getClass().getSimpleName());
    }
}


package oodesign.design.structural.facade.subsystem;

public class Facade {

    private HelpSystem01 helpSystem01;
    private HelpSystem02 helpSystem02;
    private HelpSystem03 helpSystem03;

    public Facade(){
        helpSystem01 = new HelpSystem01();
        helpSystem02 = new HelpSystem02();
        helpSystem03 = new HelpSystem03();
    }

    public void proc(){
        helpSystem01.proc();
        helpSystem02.proc();
        helpSystem03.proc();
    }
}


package oodesign.design.structural.facade;

public class Main {

    public static void main(String[] args) {
        new Facade().proc();
    }
}

Facade 가 package-private으로 정의된 HelpSystemN 클래스에 대한 입구를 제공해줌

Specific problems

Facade는 일반적으로 Singleton 으로 제공되는것이 좋다.

Facade Pattern