跳轉到內容

代理

Edit links
25% developed
來自華夏公益教科書，開放書籍，共建世界

原型 計算機科學設計模式
代理 		單例
目錄

控制對物件的訪問。

該示例首先建立了一個介面，模式在該介面上建立類。此介面僅包含一個用於顯示影像的方法，稱為displayImage()，該方法必須由所有實現它的類進行編碼。

代理類ProxyImage執行在與真實影像類本身不同的系統上，並且可以在那裡代表真實的影像RealImage。影像資訊從磁碟訪問。使用代理模式，ProxyImage的程式碼避免了多次載入影像，並以節省記憶體的方式從另一個系統訪問影像。

C# 實現
interface ICar
{
    void DriveCar() ;
}

// Real Object
public class Car : ICar
{
    public void DriveCar()
    {
        Console.WriteLine("Car has been driven!");
    }
}

// Proxy Object
public class ProxyCar : ICar
{
    private Driver driver;
    private ICar realCar;

    public ProxyCar(Driver driver)
    {
        this.driver = driver;
        this.realCar = new Car();
    }

    public void DriveCar()
    {
        if (driver.Age < 16)
            Console.WriteLine("Sorry, the driver is too young to drive.");
        else
            this.realCar.DriveCar();
     }
}

public class Driver
{
    public int Age { get; set; }

    public Driver(int age)
    {
        this.Age = age;
    }
}

// How to use above Proxy class?
private void btnProxy_Click(object sender, EventArgs e)
{
    ICar car = new ProxyCar(new Driver(15));
    car.DriveCar();

    car = new ProxyCar(new Driver(25));
    car.DriveCar();
}

輸出

Sorry, the driver is too young to drive.
Car has been driven!

注意

  • 代理可以向客戶端隱藏有關真實物件的資訊。
  • 代理可以執行最佳化，例如按需載入。
  • 代理可以執行額外的維護工作，例如審計任務。
  • 代理設計模式也被稱為替身設計模式。

另一個例子

using System;

namespace Proxy
{
    class Program
    {
        interface IImage
        {
            void Display();
        }

        class RealImage : IImage
        {
            public RealImage(string fileName)
            {
                FileName = fileName;
                LoadFromFile();
            }

            private void LoadFromFile()
            {
                Console.WriteLine("Loading " + FileName);
            }

            public String FileName { get; private set; }

            public void Display()
            {
                Console.WriteLine("Displaying " + FileName);
            }
        }

        class ProxyImage : IImage
        {
            public ProxyImage(string fileName)
            {
                FileName = fileName;
            }

            public String FileName { get; private set; }

            private IImage image;

            public void Display()
            {
                if (image == null)
                    image = new RealImage(FileName);
                image.Display();
            }
        }

        static void Main(string[] args)
        {
            IImage image = new ProxyImage("HiRes_Image");
            for (int i = 0; i < 10; i++)
                image.Display();
        }
    }
}

程式的輸出是

Loading HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
Displaying HiRes_Image
C++ 實現
#include <iostream>
#include <memory>

class ICar {
 public:
  virtual ~ICar() { std::cout << "ICar destructor!\n"; }

  virtual void DriveCar() = 0;
};

class Car : public ICar {
 public:
  void DriveCar() override { std::cout << "Car has been driven!\n"; }
};

class ProxyCar : public ICar {
 public:
  ProxyCar(int driver_age) : driver_age_(driver_age) {}

  void DriveCar() override {
    if (driver_age_ > 16) {
      real_car_->DriveCar();
    } else {
      std::cout << "Sorry, the driver is too young to drive.\n";
    }
  }

 private:
  std::unique_ptr<ICar> real_car_ = std::make_unique<Car>();
  int driver_age_;
};

int main() {
  std::unique_ptr<ICar> car = std::make_unique<ProxyCar>(16);
  car->DriveCar();

  car = std::make_unique<ProxyCar>(25);
  car->DriveCar();
}
Crystal 實現
abstract class AbstractCar
  abstract def drive
end

class Car < AbstractCar
  def drive
    puts "Car has been driven!"
  end
end

class Driver
  getter age : Int32

  def initialize(@age)
  end
end

class ProxyCar < AbstractCar
  private getter driver : Driver
  private getter real_car : AbstractCar

  def initialize(@driver)
    @real_car = Car.new
  end

  def drive
    if driver.age <= 16
      puts "Sorry, the driver is too young to drive."
    else
      @real_car.drive
    end
  end
end

# Program
driver = Driver.new(16)
car = ProxyCar.new(driver)
car.drive

driver = Driver.new(25)
car = ProxyCar.new(driver)
car.drive

輸出

Sorry, the driver is too young to drive.
Car has been driven!
Delphi 實現
// Proxy Design pattern
unit DesignPattern.Proxy;

interface

type
    // Car Interface
    ICar = interface
      procedure DriveCar;
    end;

    // TCar class, implementing ICar
    TCar = Class(TInterfacedObject, ICar)
      class function New: ICar;
      procedure DriveCar;
    End;

    // Driver Interface
    IDriver = interface
      function Age: Integer;
    end;

    // TDriver Class, implementing IDriver
    TDriver = Class(TInterfacedObject, IDriver)
    private
      FAge: Integer;
    public
      constructor Create(Age: Integer); Overload;
      class function New(Age: Integer): IDriver;
      function Age: Integer;
    End;

    // Proxy Object
    TProxyCar = Class(TInterfacedObject, ICar)
    private
      FDriver: IDriver;
      FRealCar: ICar;
    public
      constructor Create(Driver: IDriver); Overload;
      class function New(Driver: IDriver): ICar;
      procedure DriveCar;
    End;

implementation

{ TCar Implementation }

class function TCar.New: ICar;
begin
     Result := Create;
end;

procedure TCar.DriveCar;
begin
     WriteLn('Car has been driven!');
end;

{ TDriver Implementation }

constructor TDriver.Create(Age: Integer);
begin
     inherited Create;
     FAge := Age;
end;

class function TDriver.New(Age: Integer): IDriver;
begin
     Result := Create(Age);
end;

function TDriver.Age: Integer;
begin
     Result := FAge;
end;

{ TProxyCar Implementation }

constructor TProxyCar.Create(Driver: IDriver);
begin
     inherited Create;
     Self.FDriver  := Driver;
     Self.FRealCar := TCar.Create AS ICar;
end;

class function TProxyCar.New(Driver: IDriver): ICar;
begin
     Result := Create(Driver);
end;

procedure TProxyCar.DriveCar;
begin
     if (FDriver.Age <= 16)
        then WriteLn('Sorry, the driver is too young to drive.')
        else FRealCar.DriveCar();
end;

end.

用法

program Project1;
{$APPTYPE Console}
uses
    DesignPattern.Proxy in 'DesignPattern.Proxy.pas';
begin
     TProxyCar.New(TDriver.New(16)).DriveCar;
     TProxyCar.New(TDriver.New(25)).DriveCar;
end.

輸出

Sorry, the driver is too young to drive.
Car has been driven!
Java 實現

以下 Java 示例說明了“虛擬代理”模式。ProxyImage類用於訪問遠端方法。

該示例首先建立了一個介面，模式在該介面上建立類。此介面僅包含一個用於顯示影像的方法，稱為displayImage()，該方法必須由所有實現它的類進行編碼。

代理類ProxyImage執行在與真實影像類本身不同的系統上，並且可以在那裡代表真實的影像RealImage。影像資訊從磁碟訪問。使用代理模式，ProxyImage的程式碼避免了多次載入影像，並以節省記憶體的方式從另一個系統訪問影像。此示例中演示的延遲載入不是代理模式的一部分，而僅僅是使用代理所帶來的優勢。

interface Image {
    public void displayImage();
}

// On System A
class RealImage implements Image {
    private final String filename;

    /**
     * Constructor
     * @param filename
     */
    public RealImage(String filename) {
        this.filename = filename;
        loadImageFromDisk();
    }

    /**
     * Loads the image from the disk
     */
    private void loadImageFromDisk() {
        System.out.println("Loading   " + filename);
    }

    /**
     * Displays the image
     */
    public void displayImage() {
        System.out.println("Displaying " + filename);
    }
}

// On System B
class ProxyImage implements Image {
    private final String filename;
    private RealImage image;
    
    /**
     * Constructor
     * @param filename
     */
    public ProxyImage(String filename) {
        this.filename = filename;
    }

    /**
     * Displays the image
     */
    public void displayImage() {
        if (image == null) {
           image = new RealImage(filename);
        }
        image.displayImage();
    }
}

class ProxyExample {
   /**
    * Test method
    */
   public static void main(final String[] arguments) {
        Image image1 = new ProxyImage("HiRes_10MB_Photo1");
        Image image2 = new ProxyImage("HiRes_10MB_Photo2");

        image1.displayImage(); // loading necessary
        image1.displayImage(); // loading unnecessary
        image2.displayImage(); // loading necessary
        image2.displayImage(); // loading unnecessary
        image1.displayImage(); // loading unnecessary
    }
}

輸出

Loading   HiRes_10MB_Photo1
Displaying HiRes_10MB_Photo1
Displaying HiRes_10MB_Photo1
Loading   HiRes_10MB_Photo2
Displaying HiRes_10MB_Photo2
Displaying HiRes_10MB_Photo2
Displaying HiRes_10MB_Photo1
JavaScript 實現
// Driver class
class Driver {
  constructor (age) {
    this.age = age
  }
}

// Car class
class Car {
  drive () {
    console.log('Car has been driven!')
  }
}

// Proxy car class
class ProxyCar {
  constructor (driver) {
    this.car = new Car()
    this.driver = driver
  }

  drive () {
    if (this.driver.age <= 16) {
      console.log('Sorry, the driver is too young to drive.')
    } else {
      this.car.drive()
    }
  }
}

// Run program
const driver = new Driver(16)
const car = new ProxyCar(driver)
car.drive()

const driver2 = new Driver(25)
const car2 = new ProxyCar(driver2)
car2.drive()

輸出

Sorry, the driver is too young to drive.
Car has been driven!

更高階的代理涉及Proxy物件，該物件可以攔截和重新定義基本操作，例如訪問屬性。在這種情況下，處理程式函式有時被稱為陷阱。[1]

PHP 實現
<?php 

interface Image
{
    public function displayImage();
}

// On System A
class RealImage implements Image
{
    private string $filename = null;

    public function __construct(string $filename)
    {
        $this->filename = $filename;
        $this->loadImageFromDisk();
    }

    /**
     * Loads the image from the disk
     */
    private function loadImageFromDisk()
    {
        echo "Loading {$this->filename}" . \PHP_EOL;
    }

    /**
     * Displays the image
     */
    public function displayImage()
    {
    	echo "Displaying {$this->filename}" . \PHP_EOL;
    }
}

// On System B
class ProxyImage implements Image
{
    private ?Image $image = null;
    private string $filename = null;

    public function __construct(string $filename)
    {
        $this->filename = $filename;
    }

    /**
     * Displays the image
     */
    public function displayImage()
    {
        if ($this->image === null) {
           $this->image = new RealImage($this->filename);
        }
        $this->image->displayImage();
    }
}


$image1 = new ProxyImage("HiRes_10MB_Photo1");
$image2 = new ProxyImage("HiRes_10MB_Photo2");

$image1->displayImage(); // Loading necessary
$image1->displayImage(); // Loading unnecessary
$image2->displayImage(); // Loading necessary
$image2->displayImage(); // Loading unnecessary
$image1->displayImage(); // Loading unnecessary

輸出

Loading HiRes_10MB_Photo1 
Displaying HiRes_10MB_Photo1 
Displaying HiRes_10MB_Photo1 
Loading HiRes_10MB_Photo2 
Displaying HiRes_10MB_Photo2 
Displaying HiRes_10MB_Photo2 
Displaying HiRes_10MB_Photo1
Python 實現
"""
Proxy pattern example.
"""
from abc import ABCMeta, abstractmethod


NOT_IMPLEMENTED = "You should implement this."


class AbstractCar:
    __metaclass__ = ABCMeta

    @abstractmethod
    def drive(self):
        raise NotImplementedError(NOT_IMPLEMENTED)


class Car(AbstractCar):
    def drive(self) -> None:
        print("Car has been driven!")


class Driver:
    def __init__(self, age: int) -> None:
        self.age = age


class ProxyCar(AbstractCar):
    def __init__(self, driver) -> None:
        self.car = Car()
        self.driver = driver

    def drive(self) -> None:
        if self.driver.age <= 16:
            print("Sorry, the driver is too young to drive.")
        else:
            self.car.drive()


driver = Driver(16)
car = ProxyCar(driver)
car.drive()

driver = Driver(25)
car = ProxyCar(driver)
car.drive()

輸出

Sorry, the driver is too young to drive.
Car has been driven!
Rust 實現
trait ICar {
    fn drive(&self);
}

struct Car {}

impl ICar for Car {
    fn drive(&self) {
        println!("Car has been driven!");
    }
}

impl Car {
    fn new() -> Car {
        Car {}
    }
}

struct ProxyCar<'a> {
    real_car: &'a ICar,
    driver_age: i32,
}

impl<'a> ICar for ProxyCar<'a> {
    fn drive(&self) {
        if self.driver_age > 16 {
            self.real_car.drive();
        } else {
            println!("Sorry, the driver is too young to drive.")
        }
    }
}

impl<'a> ProxyCar<'a> {
    fn new(driver_age: i32, other_car: &'a ICar) -> ProxyCar {
        ProxyCar {
            real_car: other_car,
            driver_age: driver_age,
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    
    #[test]
    fn test_underage() {
        let car = Car::new();
        let proxy_car = ProxyCar::new(16, &car);
        proxy_car.drive();
    }

    #[test]
    fn test_can_drive() {
        let car = Car::new();
        let proxy_car = ProxyCar::new(17, &car);
        proxy_car.drive();
    }
}

輸出

Sorry, the car is to young for you to drive.
Car has been driven!


Clipboard

待辦事項
新增更多說明。


原型 計算機科學設計模式
代理 		單例


您對本頁有任何問題嗎？
在這裡提問


在本圖書上建立新頁面


  1. ↑ "Proxy - JavaScript | MDN". developer.mozilla.org. Retrieved 21 January 2022.
檢索自 "https://wikibook.tw/w/index.php?title=Computer_Science_Design_Patterns/Proxy&oldid=4326071"
華夏公益教科書