设计模式&委派模式（Delegate Pattern）

Delegate Pattern
委派模式（Delegate Patter n）又叫做委托模式，是一种面向对象的设计模式，允许对象组合实现与继承相同的代码重用。它的基本作用就是负责任务的调度和分发，也可以理解为是一种特殊的静态代理，但是代理模式注重的是代理的过程，而委派模式注重的是结果。委派模式属于行为模式，不属于（GOF）23种设计模式。

委托的模式涉及到两个参与者：

Deleg ato r（委托者）

Delegate（被委托者）

委托模式示例

public class RealPrinter {// 被委托者
	void print() {
		System.out.print("something");
	}
}
public class Printer {// 委托者

	RealPrinter p = new RealPrinter(); // 创建一个被委托者

	void print() {
		p.print(); // delegation
	}
}
public class MainTest {

	public static void main(String[] args) {
		Printer printer = new Printer();
        printer.print();//something
	}
}

public interface BusinessService {
    void doProcessing();
}

public class EJBService implements BusinessService{
 
    public void doProcessing() {
        System.out.println("Processing task by invoking EJB Service");
    }
 
}

public class JMSService implements BusinessService{
 
    public void doProcessing() {
        System.out.println("Processing task by invoking JMS Service");
    }
 
}

public class BusinessLookUp {
    public BusinessService getBusinessService(String serviceType){
        if (serviceType.equalsIgnoreCase("EJB")){
            return new EJBService();
        } else {
            return new JMSService();    
        }
    }
}

public class BusinessDelegate {
    private BusinessLookUp lookupService = new BusinessLookUp();
    private BusinessService businessService;
    private String serviceType;
    
    public void setServiceType(String serviceType) {
        this.serviceType = serviceType;
    }
    
    public void doTask(){
        businessService = lookupService.getBusinessService(serviceType);
        businessService.doProcessing();
    }
    
}

public class Client {
    BusinessDelegate businessDelegate;
    public Client(BusinessDelegate businessDelegate){
        this.businessDelegate = businessDelegate;
    }
    
    public void doTask(){
        businessDelegate.doTask();
    }
}