Java设计模式之代理模式

PROXY （Object Structural） 
Purpose 
Allows for object level access control by acting as a pass through 
entity or a placeholder object. 
Use When 
1 The object being represented is external to the system. 
2 Objects need to be created on demand. 
3 Access control for the original object is required. 
4 Added functionality is required when an object is accessed. 
Example 
Ledger applications often provide a way for users to reconcile 
their bank statements with their ledger data on demand, automating 
much of the process. The actual operation of communicating 
with a third party is a relatively expensive operation that should be 
limited. By using a proxy to represent the communications object 
we can limit the number of times or the intervals the communication 
is invoked. In addition, we can wrap the complex instantiation 
of the communication object inside the proxy class, decoupling 
calling code from the implementation details. 

package javaPattern.proxy;

public interface Subject {
    public void request();
}
class RealSubject implements Subject{

    @Override
    public void request() {
        System.out.println("实际类的方法");

    }

}
class Proxy implements Subject{
    private Subject real;
    public Proxy(Subject real){
        this.real = real;
    }
    @Override
    public void request() {
        System.out.println("代理以下方法");
        real.request();

    }

}
class Client{
    public static void main(String[] args) {
        Proxy proxy = new Proxy(new RealSubject());
        proxy.request();
    }
}