JQuery Ajax通过Handler访问外部XML数据的代码

JQuery Ajax通过Handler访问外部XML数据的代码_jquery

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Freigeben： 2016-05-16 18:25:55

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JQuery的使用非常简单，我们只需要从其官方网站上下载一个脚本文件并引用到页面上即可，然后你就可以在你的脚本代码中任意使用JQuery提供的对象和功能了。
　　在JQuery中使用Ajax方法异步获取服务器资源非常简单，读者可以参考其官方网站上提供的例子http://api.jquery.com/category/ajax/。当然，作为客户端脚本，JQuery也会遇到跨域访问资源的问题，什么是跨域访问呢？简单来说就是脚本所要访问的资源属于网站外部的资源，脚本所在的位置和资源所在的位置不在同一区域。默认情况下，浏览器是不允许直接进行资源的跨域访问的，除非客户端浏览器有设置，否则访问会失败。在这种情况下，我们一般都会采用在服务器端使用handler来解决，就是说在脚本和资源之间建立一个桥梁，让脚本访问本站点内的handler，通过handler去访问外部资源。这个是非常普遍的做法，而且操作起来也非常简单，因为会经常使用到，所以在此记录一下，方便日后使用！
　　首先需要在网站中创建一个handler，在Visual Studio中新建一个Generic Handler文件，拷贝下面的代码：

复制代码代码如下:

 
 
namespace WebApplication1 
{ 
using System; 
using System.IO; 
using System.Net; 
using System.Text; 
using System.Web; 
using System.Collections.Generic; 
using System.Linq; 
///  
/// Asynchronous HTTP handler for rendering external xml source. 
///  
public class Stock : System.Web.IHttpAsyncHandler 
{ 
private static readonly SafeList safeList = new SafeList(); 
private HttpContext context; 
private WebRequest request; 
///  
/// Gets a value indicating whether the HTTP handler is reusable. 
///  
public bool IsReusable 
{ 
get { return false; } 
} 
///  
/// Verify that the external RSS feed is hosted by a server on the safe list 
/// before making an asynchronous HTTP request for it. 
///  
public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData) 
{ 
var u = context.Request.QueryString["u"]; 
var uri = new Uri(u); 
if (safeList.IsSafe(uri.DnsSafeHost)) 
{ 
this.context = context; 
this.request = HttpWebRequest.Create(uri); 
return this.request.BeginGetResponse(cb, extraData); 
} 
else 
{ 
throw new HttpException(204, "No content"); 
} 
} 
///  
/// Render the response from the asynchronous HTTP request for the RSS feed 
/// using the response's Expires and Last-Modified headers when caching. 
///  
public void EndProcessRequest(IAsyncResult result) 
{ 
string expiresHeader; 
string lastModifiedHeader; 
string rss; 
using (var response = this.request.EndGetResponse(result)) 
{ 
expiresHeader = response.Headers["Expires"]; 
lastModifiedHeader = response.Headers["Last-Modified"]; 
using (var stream = response.GetResponseStream()) 
using (var reader = new StreamReader(stream, true)) 
{ 
rss = reader.ReadToEnd(); 
} 
} 
var output = this.context.Response; 
output.ContentEncoding = Encoding.UTF8; 
output.ContentType = "text/xml;"; // "application/rss+xml; charset=utf-8"; 
output.Write(rss); 
var cache = output.Cache; 
cache.VaryByParams["u"] = true; 
DateTime expires; 
var hasExpires = DateTime.TryParse(expiresHeader, out expires); 
DateTime lastModified; 
var hasLastModified = DateTime.TryParse(lastModifiedHeader, out lastModified); 
cache.SetCacheability(HttpCacheability.Public); 
cache.SetOmitVaryStar(true); 
cache.SetSlidingExpiration(false); 
cache.SetValidUntilExpires(true); 
DateTime expireBy = DateTime.Now.AddHours(1); 
if (hasExpires && expires.CompareTo(expireBy) { 
cache.SetExpires(expires); 
} 
else 
{ 
cache.SetExpires(expireBy); 
} 
if (hasLastModified) 
{ 
cache.SetLastModified(lastModified); 
} 
} 
///  
/// Do not process requests synchronously. 
///  
public void ProcessRequest(HttpContext context) 
{ 
throw new InvalidOperationException(); 
} 
} 
///  
/// Methods for matching hostnames to a list of safe hosts. 
///  
public class SafeList 
{ 
///  
/// Hard-coded list of safe hosts. 
///  
private static readonly IEnumerable hostnames = new string[] 
{ 
"cnblogs.com", 
"msn.com", 
"163.com", 
"csdn.com" 
}; 
///  
/// Prefix each safe hostname with a period. 
///  
private static readonly IEnumerable dottedHostnames = 
from hostname in hostnames 
select string.Concat(".", hostname); 
///  
/// Tests if the  matches exactly or ends with a 
/// hostname from the safe host list. 
///  
/// Hostname to test 
/// True if the hostname matches 
public bool IsSafe(string hostname) 
{ 
return MatchesHostname(hostname) || MatchesDottedHostname(hostname); 
} 
///  
/// Tests if the  ends with a hostname from the 
/// safe host list. 
///  
/// Hostname to test 
/// True if the hostname matches 
private static bool MatchesDottedHostname(string hostname) 
{ 
return dottedHostnames.Any(host => hostname.EndsWith(host, StringComparison.InvariantCultureIgnoreCase)); 
} 
///  
/// Tests if the  matches exactly with a hostname 
/// from the safe host list. 
///  
/// Hostname to test 
/// True if the hostname matches 
private static bool MatchesHostname(string hostname) 
{ 
return hostnames.Contains(hostname, StringComparer.InvariantCultureIgnoreCase); 
} 
} 
} 