如何：为请求设置缓存策略
以下示例演示如何为请求设置缓存策略。 该示例输入是一个 URI，如 http://www.contoso.com/。
示例
以下代码示例创建一个缓存策略，该策略允许从缓存使用请求的资源，前提是该资源在缓存中的存在时间未超过一天。 该示例显示一条消息，指示使用的资源是否来自缓存（例如 "The response was retrieved from the cache : False."），然后显示该资源。 可以由客户端和服务器之间的任何缓存实现请求。
using System;
using System.Net;
using System.Net.Cache;
using System.IO;
namespace Examples.System.Net.Cache
{
public class CacheExample
{
public static void UseCacheForOneDay(Uri resource)
{
// Create a policy that allows items in the cache
// to be used if they have been cached one day or less.
HttpRequestCachePolicy requestPolicy =
new HttpRequestCachePolicy (HttpCacheAgeControl.MaxAge,
TimeSpan.FromDays(1));
WebRequest request = WebRequest.Create (resource);
// Set the policy for this request only.
request.CachePolicy = requestPolicy;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
// Determine whether the response was retrieved from the cache.
Console.WriteLine ("The response was retrieved from the cache : {0}.",
response.IsFromCache);
Stream s = response.GetResponseStream ();
StreamReader reader = new StreamReader (s);
// Display the requested resource.
Console.WriteLine(reader.ReadToEnd());
reader.Close ();
s.Close();
response.Close();
}
public static void Main(string[] args)
{
if (args == null || args.Length != 1)
{
Console.WriteLine ("You must specify the URI to retrieve.");
return;
}
UseCacheForOneDay (new Uri(args[0]));
}
}
}
Imports System
Imports System.Net
Imports System.Net.Cache
Imports System.IO
Namespace Examples.System.Net.Cache
Public Class CacheExample
Public Shared Sub UseCacheForOneDay(ByVal resource As Uri)
' Create a policy that allows items in the cache
' to be used if they have been cached one day or less.
Dim requestPolicy As New HttpRequestCachePolicy _
(HttpCacheAgeControl.MaxAge, TimeSpan.FromDays(1))
Dim request As WebRequest = WebRequest.Create(resource)
' Set the policy for this request only.
request.CachePolicy = requestPolicy
Dim response As HttpWebResponse = _
CType(request.GetResponse(), HttpWebResponse)
' Determine whether the response was retrieved from the cache.
Console.WriteLine("The response was retrieved from the cache : {0}.", _
response.IsFromCache)
Dim s As Stream = response.GetResponseStream()
Dim reader As New StreamReader(s)
' Display the requested resource.
Console.WriteLine(reader.ReadToEnd())
reader.Close()
s.Close()
response.Close()
End Sub
Public Shared Sub Main(ByVal args() As String)
If args Is Nothing OrElse args.Length <> 1 Then
Console.WriteLine("You must specify the URI to retrieve.")
Return
End If
UseCacheForOneDay(New Uri(args(0)))
End Sub
End Class
End Namespace
