Pattern Facade e Proxy
Semplifichi sottosistemi complessi con Facade e controlli l'accesso agli oggetti con il pattern Proxy.
Pattern Facade e Proxy è una lezione Clean Architecture & Design Patterns in Practice gratuita su CoddyKit. Questa è la lezione 2 di 4. Puoi leggere la lezione completa qui gratuitamente — poi esercitati direttamente nel browser con un editor di codice integrato e un tutor IA disponibile 24/7. Fa parte del percorso di apprendimento Clean Architecture & Design Patterns in Practice, e i tuoi progressi si sincronizzano tra il web e l'app CoddyKit. Il corso Clean Architecture & Design Patterns in Practice include 4 lezioni in totale.
Parti di questa lezione non sono ancora state tradotte e vengono mostrate in inglese.
Welcome to Facade & Proxy!
In this lesson, we'll dive into two powerful Structural Design Patterns: the Facade and Proxy patterns.
Structural patterns help you compose objects and classes into larger structures, making systems more flexible and efficient.
We'll learn how Facade simplifies complex systems and how Proxy controls access to objects.
Meet the Facade Pattern
Imagine a complex machine with many buttons and levers. The Facade pattern provides a simple, unified interface to a set of interfaces in a subsystem.
- It defines a higher-level interface that makes the subsystem easier to use.
- Think of it as a simplified front panel for a complicated system.
Its main goal is to reduce complexity and decouple the client from the subsystem's inner workings.
Dealing with Complexity
Without a Facade, a client might need to interact with many different classes and objects within a subsystem to perform a single task.
This leads to:
- Tight coupling: Client code becomes dependent on all subsystem components.
- Increased complexity: Clients need to know too much about the subsystem's internal structure.
- Harder maintenance: Changes in the subsystem's internal parts might break client code.
How Facade Simplifies
The Facade pattern introduces a single Facade class that wraps the complex subsystem.
The Facade class:
- Knows which subsystem classes are responsible for a request.
- Delegates client requests to the appropriate subsystem objects.
- Converts complex interactions into a simple method call.
Clients interact only with the Facade, not the individual subsystem classes.
Facade in Action: Home Theater
Let's see a simple example with a home theater system. Instead of turning on the TV, amplifier, and DVD player separately, a Facade does it all.
public class Amplifier {
public void on() { System.out.println("Amplifier On"); }
public void setDvd(DvdPlayer dvd) { System.out.println("Amplifier setting DVD"); }
public void setVolume(int volume) { System.out.println("Amplifier volume " + volume); }
public void off() { System.out.println("Amplifier Off"); }
}
public class DvdPlayer {
public void on() { System.out.println("DVD Player On"); }
public void play(String movie) { System.out.println("Playing movie: " + movie); }
public void off() { System.out.println("DVD Player Off"); }
}
public class Television {
public void on() { System.out.println("TV On"); }
public void off() { System.out.println("TV Off"); }
}
// The Facade
public class HomeTheaterFacade {
Amplifier amp;
DvdPlayer dvd;
Television tv;
public HomeTheaterFacade(Amplifier amp, DvdPlayer dvd, Television tv) {
this.amp = amp;
this.dvd = dvd;
this.tv = tv;
}
public void watchMovie(String movie) {
System.out.println("Get ready to watch a movie...");
tv.on();
amp.on();
amp.setDvd(dvd);
amp.setVolume(5);
dvd.on();
dvd.play(movie);
}
public void endMovie() {
System.out.println("Shutting down home theater...");
dvd.off();
amp.off();
tv.off();
}
}
public class Main {
public static void main(String[] args) {
Amplifier amp = new Amplifier();
DvdPlayer dvd = new DvdPlayer();
Television tv = new Television();
HomeTheaterFacade homeTheater = new HomeTheaterFacade(amp, dvd, tv);
homeTheater.watchMovie("Inception");
System.out.println("---");
homeTheater.endMovie();
}
}Why Use Facade?
The Facade pattern offers several key advantages:
- Simplifies client code: Clients don't need to learn the complex API of the subsystem.
- Decouples client from subsystem: Reduces dependencies, making the system more robust to changes.
- Improves testability: You can mock the Facade for easier testing of client code.
- Promotes layering: Helps structure a system into layers with clear responsibilities.
Introducing the Proxy Pattern
The Proxy pattern provides a surrogate or placeholder for another object to control access to it.
Think of it as a middleman. Instead of talking directly to the real object, you talk to its proxy.
The proxy can add extra logic before or after accessing the real object, like security checks, lazy loading, or logging.
Common Proxy Applications
Proxies are versatile and used in many scenarios:
- Protection Proxy: Controls access based on permissions (e.g., only authenticated users can access).
- Virtual Proxy: Creates expensive objects on demand (lazy loading), improving performance.
- Remote Proxy: Represents an object located in a different address space (e.g., network proxy for a remote service).
- Logging Proxy: Logs method calls to the real object.
Proxy in Action: Secure Access
Here's an example of a Protection Proxy. A user tries to access a sensitive database. The proxy checks if the user has admin rights first.
// Subject Interface
interface Database {
void executeQuery(String query);
}
// Real Subject
class RealDatabase implements Database {
public void executeQuery(String query) {
System.out.println("Executing query: " + query);
}
}
// Proxy
class DatabaseProxy implements Database {
private RealDatabase realDatabase;
private String userRole;
public DatabaseProxy(String userRole) {
this.userRole = userRole;
this.realDatabase = new RealDatabase(); // Create real object if needed, or lazily
}
public void executeQuery(String query) {
if (userRole.equals("ADMIN")) {
System.out.println("Proxy: Admin access granted.");
realDatabase.executeQuery(query);
} else {
System.out.println("Proxy: Access denied! Only ADMIN can execute queries.");
}
}
}
public class Main {
public static void main(String[] args) {
Database adminUser = new DatabaseProxy("ADMIN");
adminUser.executeQuery("SELECT * FROM sensitive_data");
System.out.println("---");
Database regularUser = new DatabaseProxy("USER");
regularUser.executeQuery("DELETE FROM sensitive_data");
}
}Why Use Proxy?
The Proxy pattern offers significant benefits:
- Controlled Access: Can restrict or enhance access to the real object.
- Lazy Initialization: Delays object creation until it's actually needed, saving resources.
- Remote Access Abstraction: Hides the complexities of accessing objects in different locations.
- Added Functionality: Can inject logging, caching, or security checks without modifying the real object.
Quick Check: Facade vs. Proxy
Consider a scenario where you have a complex image processing library with dozens of classes and methods. You want to provide a simple function like processImage(imageFile) to your users.
Which design pattern would be most suitable to achieve this simplification?
Facade & Proxy: Key Takeaways
We've explored two powerful structural patterns:
- The Facade pattern provides a simplified, high-level interface to a complex subsystem, making it easier to use and reducing coupling.
- The Proxy pattern provides a surrogate or placeholder for another object to control access to it, adding logic like security, lazy loading, or logging.
Both patterns enhance system structure and maintainability by managing complexity and controlling interactions between objects.
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Semplifichi sottosistemi complessi con Facade e controlli l'accesso agli oggetti con il pattern Proxy. Eserciti Clean Architecture & Design Patterns in Practice con codice pratico che esegui direttamente nel browser, e un tutor IA 24/7 risponde alle tue domande mentre lavori sulla lezione.
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Tutte le lezioni di questo corso
- Pattern Adapter e Decorator
- Pattern Facade e Proxy
- Pattern Composite e Bridge
- Pattern Flyweight per l'efficienza della memoria