Design Pattern - Proxy（Java）
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Definition
Provide a surrogate or placeholder for another object to control access to it.
Participants
The classes and/or objects participating in this pattern are:
- Proxy (MathProxy)
- Maintains a reference that lets the proxy access the real subject. Proxy may refer to a Subject if the RealSubject and Subject interfaces are the same.
- Provides an interface identical to Subject's so that a proxy can be substituted for the real subject.
- Controls access to the real subject and may be responsible for creating and deleting it.
- Other responsibilites depend on the kind of proxy:
- Remote proxies are responsible for encoding a request and its arguments and for sending the encoded request to the real subject in a different address space.
- Virtual proxies may cache additional information about the real subject so that they can postpone accessing it. For example, the ImageProxy from the Motivation caches the real images's extent.
- Protection proxies check that the caller has the access permissions required to perform a request.
- Subject (IMath)
- Defines the common interface for RealSubject and Proxy so that a Proxy can be used anywhere a RealSubject is expected.
- RealSubject (Math)
- Defines the real object that the proxy represents.
Sample Code in Java
This structural code demonstrates the Proxy pattern which provides a representative object (proxy) that controls access to another similar object.
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.sample;
/**
* Startup class for Structural Proxy Design Pattern.
*
* @author Chimomo
*/
class Program {
/**
* Entry point into console application.
*
* @param args The arguments
*/
public static void main(String[] args) {
// Create proxy and request a service.
Proxy proxy = new Proxy();
proxy.request();
}
}
/*
Output:
Called RealSubject.request()
*/
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.sample;
/**
* The 'Proxy' class.
*
* @author Chimomo
*/
class Proxy extends Subject {
// The real subject.
private RealSubject realSubject;
/**
* Request.
*/
@Override
public void request() {
// Use 'lazy initialization'.
if (this.realSubject == null) {
this.realSubject = new RealSubject();
}
this.realSubject.request();
}
}
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.sample;
/**
* The 'RealSubject' class.
*
* @author Chimomo
*/
class RealSubject extends Subject {
/**
* Request.
*/
@Override
public void request() {
System.out.println("Called RealSubject.request()");
}
}
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.sample;
/**
* The 'Subject' abstract class.
*
* @author Chimomo
*/
abstract class Subject {
/**
* Request.
*/
public abstract void request();
}
This real-world code demonstrates the Proxy pattern for a Math object represented by a MathProxy object.
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.realworld;
/**
* The 'Subject' interface.
*
* @author Chimomo
*/
public interface IMath {
/**
* Add.
*
* @param x The x
* @param y The y
* @return The sum of x and y
*/
double add(double x, double y);
/**
* Sub.
*
* @param x The x
* @param y The y
* @return The difference of x and y
*/
double sub(double x, double y);
/**
* Mul.
*
* @param x The x
* @param y The y
* @return The product of x and y
*/
double mul(double x, double y);
/**
* Div.
*
* @param x The x
* @param y The y
* @return The quotient of x and y
*/
double div(double x, double y);
}
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.realworld;
/**
* The 'RealSubject' class.
*
* @author Chimomo
*/
class Math implements IMath {
/**
* Add.
*
* @param x The x
* @param y The y
* @return The sum of x and y
*/
@Override
public double add(double x, double y) {
return x + y;
}
/**
* Sub.
*
* @param x The x
* @param y The y
* @return The difference of x and y
*/
@Override
public double sub(double x, double y) {
return x - y;
}
/**
* Mul.
*
* @param x The x
* @param y The y
* @return The product of x and y
*/
@Override
public double mul(double x, double y) {
return x * y;
}
/**
* Div.
*
* @param x The x
* @param y The y
* @return The quotient of x and y
*/
@Override
public double div(double x, double y) {
return x / y;
}
}
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.realworld;
/**
* The 'Proxy Object' class.
*
* @author Chimomo
*/
class MathProxy implements IMath {
// The math.
private Math math = new Math();
/**
* Add.
*
* @param x The x
* @param y The y
* @return The sum of x and y
*/
@Override
public double add(double x, double y) {
return this.math.add(x, y);
}
/**
* Sub.
*
* @param x The x
* @param y The y
* @return The difference of x and y
*/
@Override
public double sub(double x, double y) {
return this.math.sub(x, y);
}
/**
* Mul.
*
* @param x The x
* @param y The y
* @return The product of x and y
*/
@Override
public double mul(double x, double y) {
return this.math.mul(x, y);
}
/**
* Div.
*
* @param x The x
* @param y The y
* @return The quotient of x and y
*/
@Override
public double div(double x, double y) {
return this.math.div(x, y);
}
}
/*
* Chimomo's Blog: https://blog.csdn.net/chimomo/
*/
package chimomo.learning.java.designpattern.proxy.realworld;
/**
* Startup class for Real-World Proxy Design Pattern.
*
* @author Chimomo
*/
class Program {
/**
* Entry point into console application.
*
* @param args The arguments
*/
public static void main(String[] args) {
// Create math proxy.
MathProxy proxy = new MathProxy();
// Do the math.
System.out.println("4 + 2 = " + proxy.add(4, 2));
System.out.println("4 - 2 = " + proxy.sub(4, 2));
System.out.println("4 * 2 = " + proxy.mul(4, 2));
System.out.println("4 / 2 = " + proxy.div(4, 2));
}
}
/*
Output:
4 + 2 = 6.0
4 - 2 = 2.0
4 * 2 = 8.0
4 / 2 = 2.0
*/
标签：Java,Chimomo,Pattern,param,Design,proxy,double,return,chimomo 来源： https://blog.csdn.net/chimomo/article/details/80988300