今天的工作中要访问摄像机内部的一个web站点，这就涉及到jquery的ajax跨域访问的问题。我使用的是jquery1.7的版本，下面总结如下：
- 问题一：
一开始用IE调试，总是返回No Transport错误，这是因为在进行跨域访问的时候，IE8浏览器（不同的浏览器对跨域的支持不一样）不支持跨域访问，必须在ajax请求前面加上 jQuery.support.cors = true;才行。 - 问题二：跨域问题解决后，返回的xhr.statusText = "[object Error]"，并且xmlHttpReqest.readyState始终为0。
后来我更改为自己的url，可以访问，说明是跨域的问题。后来我不用jquery的ajax，用最原始的ajax在执行到open函数的时候，提示没有权限。这才知道是跨域访问没有权限的问题。
后来在项目组同事的帮助下找到了下面的解决方案：
就是通过吧url和参数发送给servlet，然后servlet再建立HttpURLConnection，把请求发送给其他的站点。当然我们的项目为了把所有发送的请求都对应一个servlet，使用的是过滤器。
first.jsp：
<!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> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> <link href="IEfile/doc/css/base.css" rel="stylesheet" type="text/css" /> <link href="IEfile/doc/css/login.css" rel="stylesheet" type="text/css" /> <script type="text/javascript" src="IEfile/doc/script/jquery-1.7.1.min.js"></script> <script type="text/javascript" src="IEfile/doc/script/jquery.cookie.js"></script> <script type="text/javascript" src="IEfile/doc/script/login.js"></script> <script type="text/javascript" src="IEfile/doc/script/common.js"></script> <script type="text/javascript" src="IEfile/doc/script/Translator.js"></script> <script type="text/javascript"> var g_lxdLogin = null; // Login.xml function DoLogin() { m_szUserPwdValue = "111";//Base64.encode("admin" + ":" + "12345"); var m_lHttp = "http://"; var m_szHostName = "localhost"; var m_lHttpPort = "8080"; var urlTest = m_lHttp + m_szHostName + ":" + m_lHttpPort + "/WebServerTest1/PSIA/Custom/SelfExt/userCheck"; alert(urlTest); $.ajax({ type: "GET", url: urlTest, async: true, timeout: 15000, beforeSend: function(xhr) { xhr.setRequestHeader("If-Modified-Since", "0"); xhr.setRequestHeader("Authorization", "Basic " + m_szUserPwdValue); }, success: function(xmlDoc, textStatus, xhr) { alert("login success"); if("200" == xmlDoc.documentElement.getElementsByTagName('statusValue')[0].childNodes[0].nodeValue) { var szUrl = decodeURI(document.URL); if(szUrl.indexOf("?page=") != -1) { var szPage = szUrl.substring(szUrl.indexOf("page=") + 5, szUrl.indexOf("¶ms=")); if(szPage.indexOf(".asp") == -1) { szPage = szPage.concat(".asp"); } var szParam = szUrl.substring(szUrl.indexOf("¶ms=") + 8, szUrl.length); $.cookie('page',szPage+"?"+szParam+"%1"); } else { $.cookie('page',null); } $.cookie('userInfo'+m_lHttpPort,m_szUserPwdValue==""?Base64.encode("anonymous:177177177177177177"):m_szUserPwdValue); window.location.href = "main.asp"; } else { if(!$('#UserName').prop("disabled")) { $('#UserName').focus(); } $('#UserName').val(''); $('#Password').val(''); alert(translator.translateNode(g_lxdLogin, 'LoginTips4')); } }, error: function(xhr, textStatus, errorThrown) { alert("login error = " + textStatus); if("timeout" == textStatus) { alert(translator.translateNode(g_lxdLogin, 'ConnectTimeoutTips')); } else { alert(translator.translateNode(g_lxdLogin, 'NetworkErrorTips')); } } }); } </script> </head> <body > <input type="button" name="b" value="TestJson" onclick="DoLogin()"/> </body> </html>
web.xml：
<!-- psia过滤器 --> <filter> <filter-name>psiaFilter</filter-name> <filter-class>com.zm.servlet.psiaFilter</filter-class> </filter> <filter-mapping> <filter-name>psiaFilter</filter-name> <url-pattern>/PSIA/*</url-pattern> </filter-mapping> <!-- 起始页面--> <welcome-file-list> <welcome-file>/IEfile/doc/page/first.jsp</welcome-file> </welcome-file-list>
psiaFilter.java：
package com.zm.servlet; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.net.HttpURLConnection; import java.net.URL; import java.net.URLConnection; import javax.servlet.*; import javax.servlet.http.*; public class psiaFilter implements javax.servlet.Filter { public void destroy() { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest req = (HttpServletRequest)(request); String uri = req.getRequestURI(); uri = uri.substring(15); String Auth = req.getHeader("Authorization"); String method = req.getMethod(); HttpServletResponse res = (HttpServletResponse)(response); //((HttpServletResponse)(response)).sendError(700, "psiaFilter" + uri + Auth); String url= "http://172.16.8.178" + uri; URL theURL = new URL(url); HttpURLConnection urlConnection = (HttpURLConnection)theURL.openConnection(); urlConnection.setReadTimeout(11); urlConnection.setRequestMethod(method); urlConnection.setRequestProperty("If-Modified-Since", "0"); urlConnection.setRequestProperty("Authorization", Auth); urlConnection.connect(); PrintWriter out = res.getWriter(); //out.println(url); InputStream in = urlConnection.getInputStream(); int c; while((c = in.read()) != -1) out.write(c); System.out.println(out.toString()); //chain.doFilter(request, response); } public void init(FilterConfig arg0) throws ServletException { } }