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

namespace CacheService {    

    // 定義如何添加、獲取、刪除欲進(jìn)行緩存的對(duì)象    
    public interface ICacheStrategy {    

        // 添加對(duì)象    
        void AddItem(string key, object obj);    

        // 獲取對(duì)象    
        object GetItem(string key);    

        // 刪除對(duì)象    
        void RemoveItem(string key);    
    }    

   
    public class DefaultCacheStrategy : ICacheStrategy {    

        private Hashtable objectStore;    

        public DefaultCacheStrategy() {    
            objectStore = new Hashtable();    
        }    

        public void AddItem(string key, object obj) {    
            objectStore.Add(key, obj);    
        }    

        public object GetItem(string key) {    
            return objectStore[key];    
        }    

        public void RemoveItem(string key) {    
            objectStore.Remove(key);    
        }    
    }    
}

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

namespace CacheService {    

    // 使用樹形結(jié)構(gòu)來(lái)存儲(chǔ)對(duì)象，有別于Hashtable的平板式結(jié)構(gòu)    
    // 通過 XPath 來(lái)進(jìn)行對(duì)象獲取    
    public class Cache {    
        private XmlElement rootMap;             //  動(dòng)態(tài)構(gòu)建的 Xml文檔 的根結(jié)點(diǎn)    
        private ICacheStrategy cacheStrategy;    
        public static readonly Cache Instance = new Cache();    // 實(shí)現(xiàn)Singleton模式    
        private XmlDocument doc = new XmlDocument();    // 構(gòu)建 Xml文檔    

        // 私有構(gòu)造函數(shù)，用來(lái)實(shí)現(xiàn)Singleton模式    
        private Cache() {    

            // 這里應(yīng)用了Strategy模式。    
            // 改進(jìn)：可以將使用何種Strategy定義到app.config中，然后使用反射來(lái)動(dòng)態(tài)創(chuàng)建類型    
            cacheStrategy = new DefaultCacheStrategy();    

            // 創(chuàng)建文檔根結(jié)點(diǎn)，用于映射 實(shí)際的數(shù)據(jù)存儲(chǔ)(例如Hashtable) 和 Xml文檔    
            rootMap = doc.CreateElement("Cache");    

            // 添加根結(jié)點(diǎn)    
            doc.AppendChild(rootMap);    
        }    

        // 根據(jù) XPath 獲取對(duì)象    
        // 先根據(jù)Xpath獲得對(duì)象的Key，然后再根據(jù)Key獲取實(shí)際對(duì)象    
        public virtual object GetItem(string xpath) {    

            object obj = null;    
            xpath = PrepareXPath(xpath);    
            XmlNode node = rootMap.SelectSingleNode(xpath);    

            if (node != null) {    
                // 獲取對(duì)象的Key    
                string key = node.Attributes["key"].Value;    

                // 獲取實(shí)際對(duì)象    
                obj = cacheStrategy.GetItem(key);    
            }    
            return obj;    
        }    

   
        // 獲取一組對(duì)象，此時(shí)xpath為一個(gè)組結(jié)點(diǎn)    
        public virtual object[] GetList(string xpath) {    
            xpath = PrepareXPath(xpath);    

            XmlNode group = rootMap.SelectSingleNode(xpath);    

            // 獲取該結(jié)點(diǎn)下的所有子結(jié)點(diǎn)(使用[@key]確保子結(jié)點(diǎn)一定包含key屬性)    
            XmlNodeList results = group.SelectNodes(xpath + "/*[@key]");    

            ArrayList objects = new ArrayList();    

            string key;    

            foreach (XmlNode result in results) {    
                key = result.Attributes["key"].Value;    
                Object obj = cacheStrategy.GetItem(key);    
                objects.Add(obj);    
            }    

            return (object[])objects.ToArray(typeof(object));    
        }    

   
        // 添加對(duì)象，對(duì)象實(shí)際上還是添加到ICacheStrategy指定的存儲(chǔ)位置，    
        // 動(dòng)態(tài)創(chuàng)建的 Xml 結(jié)點(diǎn)僅保存了對(duì)象的Id(key)，用于映射兩者間的關(guān)系    
        public virtual void AddItem(string xpath, object obj) {    

            // 獲取 Xpath，例如 /Cache/BookStore/Book/Title    
            string newXpath = PrepareXPath(xpath);    

            int separator = newXpath.LastIndexOf("/");    

            // 獲取組結(jié)點(diǎn)的層疊順序 ，例如 /Cache/BookStore/Book    
            string group = newXpath.Substring(0, separator);    

            // 獲取葉結(jié)點(diǎn)名稱，例如 Title    
            string element = newXpath.Substring(separator + 1);    

            // 獲取組結(jié)點(diǎn)    
            XmlNode groupNode = rootMap.SelectSingleNode(group);    

            // 如果組結(jié)點(diǎn)不存在，創(chuàng)建之    
            if (groupNode == null) {    
                lock (this) {    
                    groupNode = CreateNode(group);    
                }    
            }    

            // 創(chuàng)建一個(gè)唯一的 key ，用來(lái)映射 Xml 和對(duì)象的主鍵    
            string key = Guid.NewGuid().ToString();    

            // 創(chuàng)建一個(gè)新結(jié)點(diǎn)    
            XmlElement objectElement = rootMap.OwnerDocument.CreateElement(element);    

            // 創(chuàng)建結(jié)點(diǎn)屬性 key    
            XmlAttribute objectAttribute = rootMap.OwnerDocument.CreateAttribute("key");    

            // 設(shè)置屬性值為 剛才生成的 Guid    
            objectAttribute.Value = key;    

            // 將屬性添加到結(jié)點(diǎn)    
            objectElement.Attributes.Append(objectAttribute);    

            // 將結(jié)點(diǎn)添加到 groupNode 下面(groupNode為Xpath的層次部分)    
            groupNode.AppendChild(objectElement);    

            // 將 key 和 對(duì)象添加到實(shí)際的存儲(chǔ)位置，比如Hashtable    
            cacheStrategy.AddItem(key, obj);    
        }    

   
        // 根據(jù) XPath 刪除對(duì)象    
        public virtual void RemoveItem(string xpath) {    

            xpath = PrepareXPath(xpath);    
            XmlNode result = rootMap.SelectSingleNode(xpath);    

            string key;         // 對(duì)象的Id     

            // 如果 result 是一個(gè)組結(jié)點(diǎn)(含有子結(jié)點(diǎn))    
            if (result.HasChildNodes) {    

                // 選擇所有包含有key屬性的的結(jié)點(diǎn)    
                XmlNodeList nodeList = result.SelectNodes("descendant::*[@key]");    

                foreach (XmlNode node in nodeList) {    

                    key = node.Attributes["key"].Value;    

                    // 從 Xml 文檔中刪除結(jié)點(diǎn)    
                    node.ParentNode.RemoveChild(node);    

                    // 從實(shí)際存儲(chǔ)中刪除結(jié)點(diǎn)    
                    cacheStrategy.RemoveItem(key);    
                }    
            } else {        // 如果 result 是一個(gè)葉結(jié)點(diǎn)(不含子結(jié)點(diǎn))    

                key = result.Attributes["key"].Value;    
                result.ParentNode.RemoveChild(result);    
                cacheStrategy.RemoveItem(key);    
            }    
        }    

   
        // 根據(jù) XPath 創(chuàng)建一個(gè)結(jié)點(diǎn)    
        private XmlNode CreateNode(string xpath) {    

            string[] xpathArray = xpath.Split('/');    
            string nodePath = "";    

            // 父節(jié)點(diǎn)初始化    
            XmlNode parentNode = (XmlNode)rootMap;      

            // 逐層深入 XPath 各層級(jí)，如果結(jié)點(diǎn)不存在則創(chuàng)建    
            // 比如 /DvdStore/Dvd/NoOneLivesForever    
            for (int i = 1; i < xpathArray.Length; i++) {    
                XmlNode node = rootMap.SelectSingleNode(nodePath + "/" + xpathArray[i]);    

                if (node == null) {    
                    XmlElement newElement = rootMap.OwnerDocument.CreateElement(xpathArray[i]); // 創(chuàng)建結(jié)點(diǎn)    
                    parentNode.AppendChild(newElement);    
                }    

                // 創(chuàng)建新路徑，更新父節(jié)點(diǎn)，進(jìn)入下一級(jí)    
                nodePath = nodePath + "/" + xpathArray[i];    
                parentNode = rootMap.SelectSingleNode(nodePath);    
            }    

            return parentNode;    
        }    

        // 構(gòu)建 XPath，使其以 /Cache 為根結(jié)點(diǎn)，并清除多于的"/"字符    
        private string PrepareXPath(string xpath) {    
            string[] xpathArray = xpath.Split('/');    
            xpath = "/Cache";       // 這里的名稱需與構(gòu)造函數(shù)中創(chuàng)建的根結(jié)點(diǎn)名稱對(duì)應(yīng)    
            foreach (string s in xpathArray) {    
                if (s != "") {    
                    xpath += "/" + s;    
                }    
            }    
            return xpath;    
        }    

    }    
}