定义：使用多个类而不是一个去传递请求，可以很大程度上降低请求的发出者与接受者之间的耦合。多个类成链式，去接受请求，在请求的接受者接受之前传递请求。
UML图：
类：
Handler: 定义处理请求的接口
ConcreteHandler:1:处理请求
2:获取下一个链接者
3:如果这个类可以处理请求，处理；否则传递给下一个链接者。
Client: 初始化请求，发送请求。
用C#写的小例子：
using System;
namespace DoFactory.GangOfFour.Chain.Structural
{
/// <summary>
/// 责任链设计模式
/// </summary>
class MainApp
{
/// <summary>
/// 程序入口点
/// </summary>
static void Main()
{
// 新建责任链
Handler h1 = new ConcreteHandler1();
Handler h2 = new ConcreteHandler2();
Handler h3 = new ConcreteHandler3();
h1.SetSuccessor(h2);
h2.SetSuccessor(h3);
// 初始化请求
int[] requests = { 2, 5, 14, 22, 18, 3, 27, 20 };
foreach (int request in requests)
{
h1.HandleRequest(request);
}
// 等待
Console.ReadKey();
}
}
/// <summary>
/// 'Handler'接口或抽象类
/// </summary>
abstract class Handler
{
protected Handler successor;
public void SetSuccessor(Handler successor)
{
this.successor = successor;
}
public abstract void HandleRequest(int request);
}
/// <summary>
///'ConcreteHandler1' 类
/// </summary>
class ConcreteHandler1 : Handler
{
public override void HandleRequest(int request)
{
if (request >= 0 && request < 10)
{
Console.WriteLine("{0} handled request {1}",
this.GetType().Name, request);
}
else if (successor != null)
{
successor.HandleRequest(request);
}
}
}
/// <summary>
/// The 'ConcreteHandler2' class
/// </summary>
class ConcreteHandler2 : Handler
{
public override void HandleRequest(int request)
{
if (request >= 10 && request < 20)
{
Console.WriteLine("{0} handled request {1}",
this.GetType().Name, request);
}
else if (successor != null)
{
successor.HandleRequest(request);
}
}
}
/// <summary>
/// The 'ConcreteHandler3' class
/// </summary>
class ConcreteHandler3 : Handler
{
public override void HandleRequest(int request)
{
if (request >= 20 && request < 30)
{
Console.WriteLine("{0} handled request {1}",
this.GetType().Name, request);
}
else if (successor != null)
{
successor.HandleRequest(request);
}
}
}
}
现实点的例子
using System;
namespace DoFactory.GangOfFour.Chain.RealWorld
{
/// <summary>
/// MainApp startup class for Real-World
/// Chain of Responsibility Design Pattern.
/// </summary>
class MainApp
{
/// <summary>
/// Entry point into console application.
/// </summary>
static void Main()
{
// Setup Chain of Responsibility
Approver larry = new Director();
Approver sam = new VicePresident();
Approver tammy = new President();
larry.SetSuccessor(sam);
sam.SetSuccessor(tammy);
// Generate and process purchase requests
Purchase p = new Purchase(2034, 350.00, "Assets");
larry.ProcessRequest(p);
p = new Purchase(2035, 32590.10, "Project X");
larry.ProcessRequest(p);
p = new Purchase(2036, 122100.00, "Project Y");
larry.ProcessRequest(p);
// Wait for user
Console.ReadKey();
}
}
/// <summary>
/// The 'Handler' abstract class
/// </summary>
abstract class Approver
{
protected Approver successor;
public void SetSuccessor(Approver successor)
{
this.successor = successor;
}
public abstract void ProcessRequest(Purchase purchase);
}
/// <summary>
/// The 'ConcreteHandler' class
/// </summary>
class Director : Approver
{
public override void ProcessRequest(Purchase purchase)
{
if (purchase.Amount < 10000.0)
{
Console.WriteLine("{0} approved request# {1}",
this.GetType().Name, purchase.Number);
}
else if (successor != null)
{
successor.ProcessRequest(purchase);
}
}
}
/// <summary>
/// The 'ConcreteHandler' class
/// </summary>
class VicePresident : Approver
{
public override void ProcessRequest(Purchase purchase)
{
if (purchase.Amount < 25000.0)
{
Console.WriteLine("{0} approved request# {1}",
this.GetType().Name, purchase.Number);
}
else if (successor != null)
{
successor.ProcessRequest(purchase);
}
}
}
/// <summary>
/// The 'ConcreteHandler' class
/// </summary>
class President : Approver
{
public override void ProcessRequest(Purchase purchase)
{
if (purchase.Amount < 100000.0)
{
Console.WriteLine("{0} approved request# {1}",
this.GetType().Name, purchase.Number);
}
else
{
Console.WriteLine(
"Request# {0} requires an executive meeting!",
purchase.Number);
}
}
}
/// <summary>
/// Class holding request details
/// </summary>
class Purchase
{
private int _number;
private double _amount;
private string _purpose;
// Constructor
public Purchase(int number, double amount, string purpose)
{
this._number = number;
this._amount = amount;
this._purpose = purpose;
}
// Gets or sets purchase number
public int Number
{
get { return _number; }
set { _number = value; }
}
// Gets or sets purchase amount
public double Amount
{
get { return _amount; }
set { _amount = value; }
}
// Gets or sets purchase purpose
public string Purpose
{
get { return _purpose; }
set { _purpose = value; }
}
}
}