创建一个ASP.NET MVC OutputCache ActionFilterAttribute

 

使用ASP.NET MVC 框架, 简单的指定OutputCache 指令并不能达到理想的效果. 幸好, ActionFilterAttribute让你能够在 controller action执行的前后运行代码.

让我们使用类似的方法来创建OutputCache ActionFilterAttribute

[OutputCache(Duration = 60, VaryByParam = "*", CachePolicy = CachePolicy.Server)]
public ActionResult Index()
{
    // ...
} 

我们将使用命名为CachePolicy的枚举类型来指定OutputCache 特性应怎样以及在哪里进行缓存:

public enum CachePolicy
{
    NoCache = 0,
    Client = 1,
    Server = 2,
    ClientAndServer = 3
} 

1.实现client-side缓存

事实上,这是很容易的。在view呈现前,我们将增加一些HTTP头到响应流。网页浏览器将获得这些头部,并且通过使用正确的缓存设置来回应请求。如果我们设置duration为60,浏览器将首页缓存一分钟。

using System.Web.Mvc;

namespace MVCActionFilters.Web.Models
{
    public class OutputCache:System.Web.Mvc.ActionFilterAttribute 
    {
        public int Duration { get; set; }
        public CachePolicy CachePolicy { get; set; }

        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            if (CachePolicy == CachePolicy.Client || CachePolicy == CachePolicy.ClientAndServer)
            {
                if (Duration <= 0) return;

                //用于设置特定于缓存的 HTTP 标头以及用于控制 ASP.NET 页输出缓存
                HttpCachePolicyBase cache = filterContext.HttpContext.Response.Cache;
                TimeSpan cacheDuration = TimeSpan.FromSeconds(Duration);

                cache.SetCacheability(HttpCacheability.Public);
                cache.SetExpires(DateTime.Now.Add(cacheDuration));
                cache.SetMaxAge(cacheDuration);
                cache.AppendCacheExtension("must-revalidate, proxy-revalidate");
            }
        }
    }
}

2. 实现server-side缓存

Server-side 缓存有一点难度. 首要的,在输出缓存系统中,我们将不得不准备HTTP 响应为可读的。为了这样做,我们首先保存当前的HTTP context到类的一个变量中. 然后, 我们创建一个新的httpcontext ,通过它将数据写入StringWriter,同时允许读操作可以发生:

 

existingContext = System.Web.HttpContext.Current;//保存当前的HTTP context到类的一个变量中
writer = new StringWriter();
HttpResponse response = new HttpResponse(writer);
HttpContext context = new HttpContext(existingContext.Request, response)
{
    User = existingContext.User
};
System.Web.HttpContext.Current = context; 
 
 
 

 public override void OnResultExecuting(ResultExecutingContext filterContext)
        {
            if (CachePolicy == CachePolicy.Server || CachePolicy == CachePolicy.ClientAndServer)
            {
                //获取缓存实例
                cache = filterContext.HttpContext.Cache;

                // 获取缓存数据
                object cachedData = cache.Get(GenerateKey(filterContext));
                if (cachedData != null)
                {
                    // 返回缓存数据
                    cacheHit = true;
                    filterContext.HttpContext.Response.Write(cachedData);
                    filterContext.Cancel = true;
                }
                else
                {  //重新设置缓存数据
                    existingContext = System.Web.HttpContext.Current;
                    writer = new StringWriter();
                    HttpResponse response = new HttpResponse(writer);
                    HttpContext context = new HttpContext(existingContext.Request, response)
                    {
                        User = existingContext.User
                    };
                    foreach (var key in existingContext.Items.Keys)
                    {
                        context.Items[key] = existingContext.Items[key];
                    }
                    System.Web.HttpContext.Current = context;
                }
            }
        }

利用该代码,我们能从高速缓存中检索现有项,并设置了HTTP响应能够被读取。在视图呈现之后,将数据存储在高速缓存中:

public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            // 服务器端缓存?
            if (CachePolicy == CachePolicy.Server || CachePolicy == CachePolicy.ClientAndServer)
            {
                if (!cacheHit)
                {
                    // 存储原有的context
                    System.Web.HttpContext.Current = existingContext;

                    // 返回呈现的数据
                    existingContext.Response.Write(writer.ToString());

                    //增加数据到缓存
                    cache.Add(
                        GenerateKey(filterContext),
                        writer.ToString(),
                        null,
                        DateTime.Now.AddSeconds(Duration),
                        Cache.NoSlidingExpiration,
                        CacheItemPriority.Normal,
                         null);
                }
            }
        } 
 
 

你现在注意到添加了一个VaryByParam到 OutputCache ActionFilterAttribute。当缓存server-side时,我可以通过传入的参数来改变缓存存储。这个GenerateKey方法会产生一个依赖于controller,action和VaryByParam的键。

 private string GenerateKey(ControllerContext filterContext)
        {
            StringBuilder cacheKey = new StringBuilder();

            // Controller + action
            cacheKey.Append(filterContext.Controller.GetType().FullName);
            if (filterContext.RouteData.Values.ContainsKey("action"))
            {
                cacheKey.Append("_");
                cacheKey.Append(filterContext.RouteData.Values["action"].ToString());
            }

            // Variation by parameters
            List<string> varyByParam = VaryByParam.Split(;).ToList();

            if (!string.IsNullOrEmpty(VaryByParam))
            {
                foreach (KeyValuePair<string, object> pair in filterContext.RouteData.Values)
                {
                    if (VaryByParam == "*" || varyByParam.Contains(pair.Key))
                    {
                        cacheKey.Append("_");
                        cacheKey.Append(pair.Key);
                        cacheKey.Append("=");
                        cacheKey.Append(pair.Value.ToString());
                    }
                }
            }
            return cacheKey.ToString();
        }
 
 

现在你可以增加 OutputCache attribute 到应用程序的任何一个controller 与controller action中 。

[MVCActionFilters.Web.Common.OutputCache(Duration = 20, VaryByParam = "*",CachePolicy=Common.CachePolicy.Client)]
        public string Cache()
        {
            return DateTime.Now.ToString();
        }
 
 

设置CachePolicy为Common.CachePolicy.Client时,将直接在客户端缓存中读取数据。

创建一个ASP.NET MVC OutputCache ActionFilterAttribute,古老的榕树,5-wow.com

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