二十四种设计模式：责任链模式(Chain of Responsibility Pattern)

责任链模式(Chain of Responsibility Pattern)

介绍
为解除请求的发送者和接收者之间耦合，而使多个对象都有机会处理这个请求。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。

示例
有一个Message实体类，某个类对它的操作有Insert()方法。现在要求根据插入信息的字符长度，让不同的对象去处理，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。

　　MessageModel

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.ChainOfResponsibility
{
    /// <summary>
    /// Message实体类
    /// </summary>
    public class MessageModel
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="msg">Message内容</param>
        /// <param name="pt">Message发布时间</param>
        public MessageModel(string msg, DateTime pt)
        {
            this._message = msg;
            this._publishTime = pt;
        }

        private string _message;
        /// <summary>
        /// Message内容
        /// </summary>
        public string Message
        {
            get { return _message; }
            set { _message = value; }
        }

        private DateTime _publishTime;
        /// <summary>
        /// Message发布时间
        /// </summary>
        public DateTime PublishTime
        {
            get { return _publishTime; }
            set { _publishTime = value; }
        }
    }
}

　　SqlMessage

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.ChainOfResponsibility
{
    /// <summary>
    /// Sql方式操作Message
    /// </summary>
    public class SqlMessage
    {
        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns></returns>
        public bool Insert(MessageModel mm)
        {
            // 代码略
            return true;
        }
    }
}

　　AbstractExecutor

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.ChainOfResponsibility
{
    /// <summary>
    /// 抽象处理者(Handler)角色
    /// </summary>
    public abstract class AbstractExecutor
    {
        /// <summary>
        /// 抽象处理者(Handler)角色
        /// </summary>
        protected AbstractExecutor _executor;

        /// <summary>
        /// 设置责任链的上一级对象
        /// </summary>
        /// <param name="executor"></param>
        public void SetSuccessor(AbstractExecutor executor)
        {
            this._executor = executor;
        }

        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns>执行者；内容；时间</returns>
        public abstract string Insert(MessageModel mm);
    }
}

　　Employee

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.ChainOfResponsibility
{
    /// <summary>
    /// 具体处理者(ConcreteHandler)角色
    /// </summary>
    public class Employee : AbstractExecutor
    {
        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns>执行者；内容；时间</returns>
        public override string Insert(MessageModel mm)
        {
            string rtn = "";

            // 插入的信息字符数小于5
            if (mm.Message.Length < 5)
            {
                SqlMessage m = new SqlMessage();

                if (m.Insert(mm))
                {
                    rtn = "执行者：雇员" + " 内容：" + mm.Message + " 时间：" + mm.PublishTime.ToString();
                }
            }
            // 否则让上级去执行
            else if (base._executor != null)
            {
                rtn = _executor.Insert(mm);
            }

            return rtn;
        }
    }
}

　　Leader

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.ChainOfResponsibility
{
    /// <summary>
    /// 抽象处理者(Handler)角色
    /// </summary>
    public class Leader : AbstractExecutor
    {
        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns>执行者；内容；时间</returns>
        public override string Insert(MessageModel mm)
        {
            string rtn = "";

            // 插入的信息字符数小于10
            if (mm.Message.Length < 10)
            {
                SqlMessage m = new SqlMessage();

                if (m.Insert(mm))
                {
                    rtn = "执行者：主管" + " 内容：" + mm.Message + " 时间：" + mm.PublishTime.ToString();
                }
            }
            // 否则让上级去执行
            else if (base._executor != null)
            {
                rtn = _executor.Insert(mm);
            }

            return rtn;
        }
    }
}

　　Manager

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.ChainOfResponsibility
{
    /// <summary>
    /// 抽象处理者(Handler)角色
    /// </summary>
    public class Manager : AbstractExecutor
    {
        /// <summary>
        /// 插入Message
        /// </summary>
        /// <param name="mm">Message实体对象</param>
        /// <returns>执行者；内容；时间</returns>
        public override string Insert(MessageModel mm)
        {
            string rtn = "";

            // 插入的信息字符数小于15
            if (mm.Message.Length < 15)
            {
                SqlMessage m = new SqlMessage();

                if (m.Insert(mm))
                {
                    rtn = "执行者：经理" + " 内容：" + mm.Message + " 时间：" + mm.PublishTime.ToString();
                }
            }
            else
            {
                rtn = "你所插入的Message不符合要求";
            }

            return rtn;
        }
    }
}

　　Client

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using Pattern.ChainOfResponsibility;

public partial class ChainOfResponsibility : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        AbstractExecutor employee = new Employee();
        AbstractExecutor leader = new Leader();
        AbstractExecutor manager = new Manager();
        employee.SetSuccessor(leader);
        leader.SetSuccessor(manager);

        Response.Write(employee.Insert(new MessageModel("abcd", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(employee.Insert(new MessageModel("abcdefgh", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(employee.Insert(new MessageModel("abcdefghigkl", DateTime.Now)));
        Response.Write("<br />");
        Response.Write(employee.Insert(new MessageModel("abcdefghigklmnop", DateTime.Now)));
    }
}

　　运行结果
　　执行者：雇员 内容：abcd 时间：2007-4-22 20:04:41
　　执行者：主管 内容：abcdefgh 时间：2007-4-22 20:04:41
　　执行者：经理 内容：abcdefghigkl 时间：2007-4-22 20:04:41
　　你所插入的Message不符合要求