JQuery的使用非常簡單，我們只需要從其官方網站上下載一個腳本文件並引用到頁面上即可，然後你就可以在你的腳本代碼中任意使用JQuery提供的對象和功能了。
在JQuery中使用Ajax方法異步獲取服務器資源非常簡單，讀者可以參考其官方網站上提供的例子http://api.jquery.com/category/ajax/。當然，作為客戶端腳本，JQuery也會遇到跨域訪問資源的問題，什麼是跨域訪問呢？簡單來說就是腳本所要訪問的資源屬於網站外部的資源，腳本所在的位置和資源所在的位置不在同一區域。默認情況下，浏覽器是不允許直接進行資源的跨域訪問的，除非客戶端浏覽器有設置，否則訪問會失敗。在這種情況下，我們一般都會采用在服務器端使用handler來解決，就是說在腳本和資源之間建立一個橋梁，讓腳本訪問本站點內的handler，通過handler去訪問外部資源。這個是非常普遍的做法，而且操作起來也非常簡單，因為會經常使用到，所以在此記錄一下，方便日後使用！
首先需要在網站中創建一個handler，在Visual Studio中新建一個Generic Handler文件，拷貝下面的代碼：
代碼如下:
<%@ WebHandler Language="C#" Class="WebApplication1.Stock" %>
namespace WebApplication1
{
using System;
using System.IO;
using System.Net;
using System.Text;
using System.Web;
using System.Collections.Generic;
using System.Linq;
/// <summary>
/// Asynchronous HTTP handler for rendering external xml source.
/// </summary>
public class Stock : System.Web.IHttpAsyncHandler
{
private static readonly SafeList safeList = new SafeList();
private HttpContext context;
private WebRequest request;
/// <summary>
/// Gets a value indicating whether the HTTP handler is reusable.
/// </summary>
public bool IsReusable
{
get { return false; }
}
/// <summary>
/// Verify that the external RSS feed is hosted by a server on the safe list
/// before making an asynchronous HTTP request for it.
/// </summary>
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");
}
}
/// <summary>
/// Render the response from the asynchronous HTTP request for the RSS feed
/// using the response's Expires and Last-Modified headers when caching.
/// </summary>
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) <= 0)
{
cache.SetExpires(expires);
}
else
{
cache.SetExpires(expireBy);
}
if (hasLastModified)
{
cache.SetLastModified(lastModified);
}
}
/// <summary>
/// Do not process requests synchronously.
/// </summary>
public void ProcessRequest(HttpContext context)
{
throw new InvalidOperationException();
}
}
/// <summary>
/// Methods for matching hostnames to a list of safe hosts.
/// </summary>
public class SafeList
{
/// <summary>
/// Hard-coded list of safe hosts.
/// </summary>
private static readonly IEnumerable<string> hostnames = new string[]
{
"cnblogs.com",
"msn.com",
"163.com",
"csdn.com"
};
/// <summary>
/// Prefix each safe hostname with a period.
/// </summary>
private static readonly IEnumerable<string> dottedHostnames =
from hostname in hostnames
select string.Concat(".", hostname);
/// <summary>
/// Tests if the <paramref name="hostname" /> matches exactly or ends with a
/// hostname from the safe host list.
/// </summary>
/// <param name="hostname">Hostname to test</param>
/// <returns>True if the hostname matches</returns>
public bool IsSafe(string hostname)
{
return MatchesHostname(hostname) || MatchesDottedHostname(hostname);
}
/// <summary>
/// Tests if the <paramref name="hostname" /> ends with a hostname from the
/// safe host list.
/// </summary>
/// <param name="hostname">Hostname to test</param>
/// <returns>True if the hostname matches</returns>
private static bool MatchesDottedHostname(string hostname)
{
return dottedHostnames.Any(host => hostname.EndsWith(host, StringComparison.InvariantCultureIgnoreCase));
}
/// <summary>
/// Tests if the <paramref name="hostname" /> matches exactly with a hostname
/// from the safe host list.
/// </summary>
/// <param name="hostname">Hostname to test</param>
/// <returns>True if the hostname matches</returns>
private static bool MatchesHostname(string hostname)
{
return hostnames.Contains(hostname, StringComparer.InvariantCultureIgnoreCase);
}
}
}
我給出的例子中是想通過Ajax異步取得msn站點上微軟的股票信息，其外部資源地址為http://money.service.msn.com/StockQuotes.aspx?symbols=msft，我們在頁面上這樣使用JQuery api通過Handler來訪問數據：
代碼如下:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript" src="jquery-1.3.2.min.js"></script>
</head>
<body>
<div id="con">
<span id="loader">loading...</span>
</div>
<script type="text/javascript">
function getData() {
$("#loader").ajaxStart(function() {
$(this).show();
});
$("#loader").ajaxComplete(function() {
$(this).hide();
});
$.ajax({
type: "GET",
url: "Stock.ashx?u=http://money.service.msn.com/StockQuotes.aspx?symbols=msft",
dataType: "xml",
success: function(data) {
var last = "";
var change = "";
var percentchange = "";
var volume = "";
var cap = "";
var yearhigh = "";
var yearlow = "";
$(data).find('ticker').each(function() {
last = $(this).attr('last');
change = $(this).attr('change');
percentchange = $(this).attr('percentchange');
volume = $(this).attr('volume');
cap = $(this).attr('marketcap');
yearhigh = $(this).attr('yearhigh');
yearlow = $(this).attr('yearlow');
document.getElementById('con').innerHTML = '<span>name:' + last + ' high:' + volume + ' low:' + cap + '</span>';
})
}
});
}
$(window).load(getData);
</script>
</body>
</html>
下面是實現的結果：
name:25.8 high:67,502,221 low:$226,107,039,514
Handler的寫法基本都大同小異，因此可以寫成一個通用的例子，以後如遇到在腳本中需要跨域訪問資源時便可以直接使用！代碼記錄於此，方便查閱。