职责链模式 - 设计模式学习

　　职责链模式(Chain of Responsibility)：使多个对象都有机会处理请求，从而避免请求的发送者和接受者之间的耦合关系。将这个对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它位置。

　　下面给出职责链模式的结构图：

　　　　


　　　　下面给出职责链模式的基本代码结构：

namespace ConsoleApplication1
{
//Handler类，定义一个处理请示的接口
abstract class Handler
{
protected Handler successor;

public void SetSuccessor(Handler successor)
{
this.successor = successor;
}

public abstract void HandleRequest(int request);
}

//ConcreteHandler1类，具体处理者类，处理它所负责的请求，可访问它的后继者，如果可处理该请求，就处理，否则将请求转发给它的后继者。
class ConcreteHandler1 : Handler
{
public override void HandleRequest(int request)
{
if (request >= 0 && request < 10)   //0到10处理此请求
{
Console.WriteLine("{0}处理请求{1}", this.GetType().Name, request);
}
else if (successor != null)
{
successor.HandleRequest(request);  //转移到下一位
}
}
}

//ConcreteHandler2类，具体处理者，当请求数在10到20之间则有权处理，否则转到下一位
class ConcreteHandler2 : Handler
{
public override void HandleRequest(int request)
{
if (request >= 10 && request < 20)
{
Console.WriteLine("{0}处理请求{1}",this.GetType().Name,request);
}
else if (successor != null)
{
successor.HandleRequest(request);
}
}
}

//ConcreteHandler3类，具体处理者，当请求数在20到30之间则有权处理，否则转到下一位
class ConcreteHandler3 : Handler
{
public override void HandleRequest(int request)
{
if (request >= 20 && request < 30)
{
Console.WriteLine("{0}处理请求{1}", this.GetType().Name, request);
}
else if (successor != null)
{
successor.HandleRequest(request);
}
}
}

class Program
{
static void Main(string[] args)
{
Handler h1 = new ConcreteHandler1();
Handler h2 = new ConcreteHandler2();
Handler h3 = new ConcreteHandler3();

h1.SetSuccessor(h2);    //设置h1的后继者，当它处理不了的时候，会将请求传给后继者
h2.SetSuccessor(h3);    //设置h2的后继者，当它处理不了的时候，会将请求传给后继者

int[] requests = { 2, 5, 14, 22, 18, 3, 27, 20 };

foreach (int request in requests)
{
h1.HandleRequest(request);　　//这样还有一个好处，只要将请求给h1，它就会自动找人搞定，不会像某某部门一样踢皮球
}

Console.ReadKey();
}
}
}

　　结果如下所示：

　　　　


　　当客户端提交一个请求，请求是沿链传递直至有一个ConcreteHandler对象负责处理它。这就使得接收者和发送者都没有对方的明确信息，且链中的对象自己也不知道链的结构。结果是职责链可简化对象的相互连接，他们仅需保持一个指向其后继的引用而不需保持它所有的候选接收者的引用。同时你也可以随时增加或修改处理一个请求的结构，增强了给对象指派职责的灵活性。

　　但是要当心，因为一个请求极有可能到了链的末端都得不到处理，或者因为没有正确配置而得不到处理。所以需要事先考虑全面。

　　下面回到《大话设计模式》中的加薪代码：

namespace ConsoleApplication1
{
//申请
class Request
{
//申请类别
private string requestType;
public string RequestType
{
get { return requestType; }
set { requestType = value; }
}

//申请内容
private string requestContent;
public string RequestContent
{
get { return requestContent; }
set { requestContent = value; }
}

//数量
private int number;
public int Number
{
get { return number; }
set { number = value; }
}
}

//管理者
abstract class Manager
{
protected string name;

//管理者的上级
protected Manager superior;

public Manager(string name)
{
this.name = name;
}

//设置管理者上级
public void SetSuperior(Manager superior)
{
this.superior = superior;
}

//申请请求
abstract public void RequestApplications(Request request);
}

//经理
class CommonManager : Manager
{
public CommonManager(string name)
: base(name)
{ }

public override void RequestApplications(Request request)
{
if (request.RequestType == "请假" && request.Number <= 2)
{
Console.WriteLine("{0}:{1}数量{2}被批准", name, request.RequestContent, request.Number);
}
else
{
if (superior != null)
{
superior.RequestApplications(request);
}
}
}
}

//总监
class Majordomo : Manager
{
public Majordomo(string name)
: base(name)
{ }

public override void RequestApplications(Request request)
{
if (request.RequestType == "请假" && request.Number <= 5)
{
Console.WriteLine("{0}:{1}数量{2}被批准", name, request.RequestContent, request.Number);
}
else
{
if (superior != null)
{
superior.RequestApplications(request);
}
}
}
}

//总经理
class GeneralManager : Manager
{
public GeneralManager(string name)
: base(name)
{ }

public override void RequestApplications(Request request)
{
if (request.RequestType == "请假")
{
Console.WriteLine("{0}:{1}数量{2}被批准", name, request.RequestContent, request.Number);
}
else if (request.RequestType == "加薪" && request.Number <= 500)
{
Console.WriteLine("{0}:{1}数量{2}被批准",name,request.RequestContent,request.Number);
}
else if (request.RequestType == "加薪" && request.Number > 500)
{
Console.WriteLine("{0}:{1}数量{2}，再说吧", name, request.RequestContent, request.Number);
}
}
}

class Program
{
static void Main(string[] args)
{
CommonManager jinli = new CommonManager("金利");
Majordomo zongjian = new Majordomo("宗剑");
GeneralManager zongjinli = new GeneralManager("钟金丽");
jinli.SetSuperior(zongjian);    //设置经理上级
zongjian.SetSuperior(zongjinli);    //设置总监上级

Request request = new Request();
request.RequestType = "请假";
request.RequestContent = "小菜请假";
request.Number = 1;
jinli.RequestApplications(request);

Request request2 = new Request();
request2.RequestType = "请假";
request2.RequestContent = "小菜请假";
request2.Number = 4;
jinli.RequestApplications(request2);

Request request3 = new Request();
request3.RequestType = "加薪";
request3.RequestContent = "小菜请求加薪";
request3.Number = 500;
jinli.RequestApplications(request3);

Request request4 = new Request();
request4.RequestType = "加薪";
request4.RequestContent = "小菜请求加薪";
request4.Number = 1000;
jinli.RequestApplications(request4);

Console.ReadKey();
}
}
}

　　结果如图所示：