职责链设计模式解析-优快云博客

一. 简述

为了避免请求的发送者和接收者之间的耦合关系，使多个接受对象都有机会处理请求。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。通俗一点说就是，当客户提交一个请求时，从第一个对象开始，链中收到请求的对象要么亲自处理它，要么转发给链中的下一个候选者。提交请求的对象并不知道哪一个对象将会处理它。当然职责链中也可能没有可以处理该请求的对象，这种情况是允许发生的。

属于行为型模式。

二. 组成

抽象处理者(Handler)角色：定义出一个处理请求的接口。如果需要，接口可以定义出一个方法，以设定和返回对下家的引用。这个角色通常由一个抽象类或接口实现。
具体处理者(ConcreteHandler)角色：具体处理者接到请求后，可以选择将请求处理掉，或者将请求传给下家。由于具体处理者持有对下家的引用，因此，如果需要，具体处理者可以访问下家。

三. UML类图

四. 基本代码

public interface Handler {
	public void handleRequest(Request request);
}

public class HandlerStudent implements Handler {
	// 下一个Handler对象
	private Handler nextSuccessor;
	
	public HandlerStudent(Handler nextSuccessor) {
	   this.nextSuccessor = nextSuccessor;
	}
	
	public void handleRequest(Request request) {
	   // 处理 StudentRequest
	   if (request.getType().equalsIgnoreCase("StudentRequest")) {
	   		System.out.println("HandlerStudent begin to response StudentRequest;");
	    	request.execute();
	   }
	   // 把请求传递给其它受理者
	   else {
		    if (this.nextSuccessor != null) {
		     		nextSuccessor.handleRequest(request);
		    } else {
		     	System.out.println("request[" + request.getType() + "] has not handler to deal!");
		    }
	   }
	}
}

public class HandlerSchoolmaster implements Handler {
	// 下一个Handler对象
	private Handler nextSuccessor;
	
	public HandlerSchoolmaster(Handler nextSuccessor) {
	   this.nextSuccessor = nextSuccessor;
	}
	
	public void handleRequest(Request request) {
	   // 处理 SchoolmasterRequest
	   if (request.getType().equalsIgnoreCase("SchoolmasterRequest")) {
		    System.out.println("HandlerSchoolmaster begin to response StudentRequest;");
		    request.execute();
	   } else {		// 把请求传递给其它受理者
		    if (this.nextSuccessor != null) {
		     		nextSuccessor.handleRequest(request);
		    } else {
		     		System.out.println("request[" + request.getType() + "] has not handler to deal!");
		    }
	   }
	}
}

public class HandlerTeacher implements Handler {
	// 下一个Handler对象
	private Handler nextSuccessor;
	
	public HandlerTeacher(Handler nextSuccessor) {
	   this.nextSuccessor = nextSuccessor;
	}
	
	public void handleRequest(Request request) {
	   if (request.getType().equalsIgnoreCase("TeacherRequest")) {
		    System.out.println("HandlerTeacher begin to response StudentRequest;");
		    request.execute();
	   } else {		// 把请求传递给其它受理者
		    if (this.nextSuccessor != null) {
		     		nextSuccessor.handleRequest(request);
		    } else {
		     		System.out.println("request[" + request.getType() + "] has not handler to deal!");
		    }
	   }
	}
}

//以下是提出请求的类
/*请求类接口*/
public interface Request {
	// 请求类型
	public String getType();
	
	// 执行任务
	public void execute();
}

public class RequestPresident implements Request {
	public void execute() {
	   System.out.println("[RequestPresident] :\t Presidents request has been accepted!");
	}
	
	public String getType() {
	   return "PresidentRequest";
	}
}

public class RequestSchoolmaster implements Request {
	public void execute() {
	   System.out.println("[RequestSchoolmaster] :\t Schoolmasters request has been accepted!");
	}
	
	public String getType() {
	   return "SchoolmasterRequest";
	}
}

public class RequestStudent implements Request {
	public void execute() {
	   System.out.println("[RequestStudent] :\t Students request has been accepted!");
	}
	
	public String getType() {
	   return "StudentRequest";
	}
}

public class RequestTeacher implements Request {
	public void execute() {
	   System.out.println("[RequestTeacher] :\t Teachers request has been accepted!");
	}
	
	public String getType() {
	   return "TeacherRequest";
	}
}

//客户端
public class TestCoR {
	public static void main(String[] args) {
	   // 这就是生成的一条职责链
	   //个人认为关键在这里
	   Handler handler = new HandlerTeacher(new HandlerStudent(new HandlerSchoolmaster(null)));
	
	   Request studentReq = new RequestStudent();
	   Request teacherReq = new RequestTeacher();
	   Request schoolmasterReq = new RequestSchoolmaster();
	   Request presidentReq = new RequestPresident();
	
	   // 传入student request
	   handler.handleRequest(studentReq);
	   System.out.println("-----------");
	   // 传入teacher request
	   handler.handleRequest(teacherReq);
	   System.out.println("-----------");
	   // 传入schoolmaster request
	   handler.handleRequest(schoolmasterReq);
	   System.out.println("-----------");
	   // 传入president request
	   handler.handleRequest(presidentReq);
	   System.out.println("-----------");
	}
}