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asp.net SAF 中緩存服務(wù)的實(shí)現(xiàn)第5/5頁

更新時(shí)間：2008年08月08日 21:28:49 作者：

對(duì)緩存的興趣源于張子陽寫的一篇文章《SAF 中緩存服務(wù)的實(shí)現(xiàn)》中的一個(gè)例子：

全部代碼：
ICacheStrategy.cs

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);     
        }     
    }     
}

Cache.cs

復(fù)制代碼代碼如下:

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)來存儲(chǔ)對(duì)象，有別于Hashtable的平板式結(jié)構(gòu)     
    // 通過 XPath 來進(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;     
        }     

    }     
} 