很多情况下需要用到缓存，合理利用缓存一方面可以提高程序的响应速度，同时可以减少对特定资源访问的压力。为了避免每次请求都去访问后台的
资源（例如数据库），一般会考虑将一些更新不是很频繁的、可以重用的数据，通过一定的方式临时地保存起来，后续的请求根据情况可以直接访问这
些保存起来的数据，这种机制就是所谓的缓存机制。
.net 4.0的缓存功能主要由三部分组成：system.runtime.caching，system.web.caching.cache和output cache。
memorycache：这个是在.net 4.0中新增的缓存框架，namespace:system.runtime.caching ，assembly:system.runtime.caching.dll。
system.web.caching.cache：这个是在.net 2.0开始就一直存在的缓存对象，一般主要用在web中，当然也可以用于winform里面，不过要引用
system.web.dll。
output cache：这个是在asp.net里面使用的。在asp.net 4.0之前，都是直接使用system.web.caching.cache来缓存html片段。在asp.net 4.0
中对它进行了重新设计，提供了一个outputcacheprovider供开发人员进行扩展，但是它默认情况下，仍然使用system.web.caching.cache来做做缓存。
下面演示memorycache的简单使用：
1、添加一个类，命名为confighelper，代码如下：
/// <summary>
/// 配置帮助类
/// </summary>
class confighelper
{
/// <summary>
/// 获取管理配置文件对象
/// </summary>
/// <param name="configpath">指定要管理的配置文件路径，如果为空或不存在，则为管理程序集默认的配置文件路径。</param>
/// <returns></returns>
private static configuration getconfiguration(string configpath = null)
{
if (!string.isnullorempty(configpath) && file.exists(configpath))
{
execonfigurationfilemap map = new execonfigurationfilemap
{
execonfigfilename = configpath
};
return configurationmanager.openmappedexeconfiguration(map, configurationuserlevel.none);
}
else
{
return configurationmanager.openexeconfiguration(configurationuserlevel.none);
}
}
/// <summary>
/// 获取指定配置文件+配置名称的配置项的值
/// </summary>
public static string getappsettingvalue(string key, string defaultvalue = null, string configpath = null)
{
var config = getconfiguration(configpath);
var appsetting = config.appsettings.settings[key];
return appsetting.value;
}
/// <summary>
/// 获取所有配置值
/// </summary>
public static dictionary<string, string> getappsettingvalues(string configpath = null)
{
dictionary<string, string> settingdic = new dictionary<string, string>();
var config = getconfiguration(configpath);
var settings = config.appsettings.settings;
foreach (string key in settings.allkeys)
{
settingdic[key] = settings[key].tostring();
}
return settingdic;
}
/// <summary>
/// 设置配置值（存在则更新，不存在则新增。）
/// </summary>
public static void setappsettingvalue(string key, string value, string configpath = null)
{
var config = getconfiguration(configpath);
var setting = config.appsettings.settings[key];
if (setting == null)
{
config.appsettings.settings.add(key, value);
}
else
{
setting.value = value;
}
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("appsettings");
}
/// <summary>
/// 设置多个配置值（存在则更新，不存在则新增）
/// </summary>
public static void setappsettingvalues(ienumerable<keyvaluepair<string, string>> settingvalues, string configpath = null)
{
var config = getconfiguration(configpath);
foreach (var item in settingvalues)
{
var setting = config.appsettings.settings[item.key];
if (setting == null)
{
config.appsettings.settings.add(item.key, item.value);
}
else
{
setting.value = item.value;
}
}
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("appsettings");
}
/// <summary>
/// 删除配置值
/// </summary>
public static void removeappsetting(string key, string configpath = null)
{
var config = getconfiguration(configpath);
config.appsettings.settings.remove(key);
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("appsettings");
}
/// <summary>
/// 删除多个配置值
/// </summary>
public static void removeappsettings(string configpath = null, params string[] keys)
{
var config = getconfiguration(configpath);
if (keys != null)
{
foreach (string key in keys)
{
config.appsettings.settings.remove(key);
}
}
else
{
config.appsettings.settings.clear();
}
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("appsettings");
}
/// <summary>
/// 获取连接字符串
/// </summary>
public static string getconnectionstring(string name, string defaultconnstring = null, string configpath = null)
{
var config = getconfiguration(configpath);
var connstringsettings = config.connectionstrings.connectionstrings[name];
if (connstringsettings == null)
{
return defaultconnstring;
}
return connstringsettings.connectionstring;
}
/// <summary>
/// 获取指定配置文件+连接名称的连接字符串配置项
/// </summary>
public static connectionstringsettings getconnectionstringsetting(string name, string configpath = null)
{
var config = getconfiguration(configpath);
var connstringsettings = config.connectionstrings.connectionstrings[name];
return connstringsettings;
}
/// <summary>
/// 获取所有的连接字符串配置项
/// </summary>
public static dictionary<string, connectionstringsettings> getconnectionstringsettings(string configpath = null)
{
var config = getconfiguration(configpath);
var connstringsettingdic = new dictionary<string, connectionstringsettings>();
var connstringsettings = configurationmanager.connectionstrings;
foreach (connectionstringsettings item in connstringsettings)
{
connstringsettingdic[item.name] = item;
}
return connstringsettingdic;
}
/// <summary>
/// 设置连接字符串的值（存在则更新，不存在则新增。）
/// </summary>
public static void setconnectionstring(string name, string connstring, string provider, string configpath = null)
{
var config = getconfiguration(configpath);
connectionstringsettings connstringsettings = config.connectionstrings.connectionstrings[name];
if (connstringsettings != null)
{
connstringsettings.connectionstring = connstring;
connstringsettings.providername = provider;
}
else
{
connstringsettings = new connectionstringsettings(name, connstring, provider);
config.connectionstrings.connectionstrings.add(connstringsettings);
}
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("connectionstrings");
}
/// <summary>
/// 设置多个连接字符串的值（存在则更新，不存在则新增。）
/// </summary>
public static void setconnectionstrings(ienumerable<connectionstringsettings> connstringsettings, string configpath = null)
{
var config = getconfiguration(configpath);
foreach (var item in connstringsettings)
{
connectionstringsettings connstringsetting = config.connectionstrings.connectionstrings[item.name];
if (connstringsetting != null)
{
connstringsetting.connectionstring = item.connectionstring;
connstringsetting.providername = item.providername;
}
else
{
config.connectionstrings.connectionstrings.add(item);
}
}
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("connectionstrings");
}
/// <summary>
/// 删除连接字符串配置项
/// </summary>
public static void removeconnectionstring(string name, string configpath = null)
{
var config = getconfiguration(configpath);
config.connectionstrings.connectionstrings.remove(name);
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("connectionstrings");
}
/// <summary>
/// 删除多个连接字符串配置项
/// </summary>
public static void removeconnectionstrings(string configpath = null, params string[] names)
{
var config = getconfiguration(configpath);
if (names != null)
{
foreach (string name in names)
{
config.connectionstrings.connectionstrings.remove(name);
}
}
else
{
config.connectionstrings.connectionstrings.clear();
}
config.save(configurationsavemode.modified);
configurationmanager.refreshsection("connectionstrings");
}
}
2、添加一个类，命名为memorycachehelper（注意需引用system.runtime.caching.dll），代码如下：
/// <summary>
/// 内存缓存帮助类，支持绝对过期时间、滑动过期时间、文件依赖三种缓存方式。
/// </summary>
class memorycachehelper
{
private static readonly object _locker1 = new object(), _locker2 = new object();
/// <summary>
/// 取缓存项，如果不存在则返回空。
/// </summary>
/// <typeparam name="t"></typeparam>
/// <param name="key"></param>
/// <returns></returns>
public static t getcacheitem<t>(string key)
{
try
{
return (t)memorycache.default[key];
}
catch
{
return default(t);
}
}
/// <summary>
/// 是否包含指定键的缓存项
/// </summary>
/// <param name="key"></param>
/// <returns></returns>
public static bool contains(string key)
{
return memorycache.default.contains(key);
}
/// <summary>
/// 取缓存项，如果不存在则新增缓存项。
/// </summary>
/// <typeparam name="t"></typeparam>
/// <param name="key"></param>
/// <param name="cachepopulate"></param>
/// <param name="slidingexpiration"></param>
/// <param name="absoluteexpiration"></param>
/// <returns></returns>
public static t getoraddcacheitem<t>(string key, func<t> cachepopulate, timespan? slidingexpiration = null, datetime? absoluteexpiration = null)
{
if (string.isnullorwhitespace(key)) throw new argumentexception("invalid cache key");
if (cachepopulate == null) throw new argumentnullexception("cachepopulate");
if (slidingexpiration == null && absoluteexpiration == null) throw new argumentexception("either a sliding expiration or absolute must be provided");
if (memorycache.default[key] == null)
{
lock (_locker1)
{
if (memorycache.default[key] == null)
{
t cachevalue = cachepopulate();
if (!typeof(t).isvaluetype && cachevalue == null) //如果是引用类型且为null则不存缓存
{
return cachevalue;
}
var item = new cacheitem(key, cachevalue);
var policy = createpolicy(slidingexpiration, absoluteexpiration);
memorycache.default.add(item, policy);
}
}
}
return (t)memorycache.default[key];
}
/// <summary>
/// 取缓存项，如果不存在则新增缓存项。
/// </summary>
/// <typeparam name="t"></typeparam>
/// <param name="key"></param>
/// <param name="cachepopulate"></param>
/// <param name="dependencyfilepath"></param>
/// <returns></returns>
public static t getoraddcacheitem<t>(string key, func<t> cachepopulate, string dependencyfilepath)
{
if (string.isnullorwhitespace(key)) throw new argumentexception("invalid cache key");
if (cachepopulate == null) throw new argumentnullexception("cachepopulate");
if (memorycache.default[key] == null)
{
lock (_locker2)
{
if (memorycache.default[key] == null)
{
t cachevalue = cachepopulate();
if (!typeof(t).isvaluetype && cachevalue == null) //如果是引用类型且为null则不存缓存
{
return cachevalue;
}
var item = new cacheitem(key, cachevalue);
var policy = createpolicy(dependencyfilepath);
memorycache.default.add(item, policy);
}
}
}
return (t)memorycache.default[key];
}
/// <summary>
/// 指定缓存项的一组逐出和过期详细信息
/// </summary>
/// <param name="slidingexpiration"></param>
/// <param name="absoluteexpiration"></param>
/// <returns></returns>
private static cacheitempolicy createpolicy(timespan? slidingexpiration, datetime? absoluteexpiration)
{
var policy = new cacheitempolicy();
if (absoluteexpiration.hasvalue)
{
policy.absoluteexpiration = absoluteexpiration.value;
}
else if (slidingexpiration.hasvalue)
{
policy.slidingexpiration = slidingexpiration.value;
}
policy.priority = cacheitempriority.default;
return policy;
}
/// <summary>
/// 指定缓存项的一组逐出和过期详细信息
/// </summary>
/// <param name="filepath"></param>
/// <returns></returns>
private static cacheitempolicy createpolicy(string filepath)
{
cacheitempolicy policy = new cacheitempolicy();
policy.changemonitors.add(new hostfilechangemonitor(new list<string>() { filepath }));
policy.priority = cacheitempriority.default;
return policy;
}
/// <summary>
/// 移除指定键的缓存项
/// </summary>
/// <param name="key"></param>
public static void removecacheitem(string key)
{
if (contains(key))
{
memorycache.default.remove(key);
}
}
}
3、添加一个winform窗体，命名为main，并添加一个按钮。
4、配置app.config：
<?xml version="1.0" encoding="utf-8" ?> <configuration> <startup> <supportedruntime version="v4.0" sku=".netframework,version=v4.6.1" /> </startup> <connectionstrings> <add name ="connstring" connectionstring="server=.;database=db_test;uid=sa;pwd=********;" /> </connectionstrings> </configuration>
5、main窗体代码如下：
private void button1_click(object sender, eventargs e)
{
int times1 = 0, times2 = 0;
for (int i = 0; i < 10; i++)
{
if (memorycachehelper.contains("connstring"))
{
times1++;
}
else
{
times2++;
string connstr = memorycachehelper.getoraddcacheitem("connstring", () =>
{
return confighelper.getconnectionstring("connstring", null);
}, application.startuppath + @"\app.config");
}
}
messagebox.show($"内存缓存读取次数：{times1}，非内存缓存读取次数：{times2}", "提示", messageboxbuttons.ok, messageboxicon.information);
}
6、运行结果如下：
参考自：
黄山市民网：https://www.huangshanshimin.com/
