1、XMLHttpRequest升级版已经实现了跨域请求。不过需要在后台设置:header("Access-Control-Allow-Origin:http://www.a.com");表示某个域下允许跨域访问。
2、IE：需要使用XDomainRequest()。同样需要在后台设置：response.addHeader("Access-Control-Allow-Origin","*");
3、如果后台语言为java的话，需要自己写一个CrossDomainFilter，在过滤器中设置跨域访问，否则上传不成功。
下面以一个ajax文件上传的例子来说明跨域问题：
前台代码：
1 <!DOCTYPE html>
2 <html>
3 <head>
4 <meta charset="UTF-8">
5 <title></title>
6 </head>
7 <body>
8 <form action="" method="post" onsubmit="return false;">
9 <input type="file" name="myFile" id="myFile" value=""/>
10 <input type="button" id="btn" value="上传" /><br />
11 </form>
12 <progress id="progress" max="100" value="0" style="margin-top:10px;"></progress>
13 </body>
14 </html>
15 <script type="text/javascript">
16 window.onload = function(){
17 var oBtn = document.getElementById("btn");
18 var oFile = document.getElementById("myFile");
19 var oProgress = document.getElementById("progress");
20 oBtn.onclick = function(){
21 if(oFile.files.length <=0)return;
22 //TODO:这里假定只是单文件上传
23 var formData = new FormData();
24 formData.append("file",oFile.files[0]);
25
26 var xhr = new XMLHttpRequest();
27 xhr.upload.onprogress = function(ev){
28 ev = ev || window.event;
29 if(ev.lengthComputable)oProgress.value = parseInt(ev.loaded/ev.total*100);
30 }
31 xhr.upload.onload = function(){
32 oProgress.value = 100;
33 }
34 xhr.open("POST","http://127.0.0.1:8080/ajax5.do",true);
35 xhr.send(formData);
36 }
37
38 }
39 </script>
后台代码：
1 package com.sgepit.ajax;
2
3 import java.io.File;
4 import java.io.IOException;
5 import java.util.List;
6 import java.util.UUID;
7
8 import javax.servlet.ServletException;
9 import javax.servlet.annotation.WebServlet;
10 import javax.servlet.http.HttpServlet;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13 import javax.servlet.http.HttpSessionContext;
14
15 import org.apache.commons.fileupload.FileItem;
16 import org.apache.commons.fileupload.disk.DiskFileItemFactory;
17 import org.apache.commons.fileupload.servlet.ServletFileUpload;
18
19
20 /**
21 * @author tengri
22 *文件上传
23 */
24 @SuppressWarnings("all")
25 @WebServlet("/ajax5.do")
26 public class Ajax5 extends HttpServlet {
27
28 @Override
29 protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
30 this.doPost(req, resp);
31 }
32
33 @Override
34 protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
35 DiskFileItemFactory factory = new DiskFileItemFactory();
36 factory.setSizeThreshold(2014 * 1024);
37 factory.setRepository(new File("D:/uploadTemp"));
38 ServletFileUpload upload = new ServletFileUpload(factory);
39 resp.setCharacterEncoding("utf-8");
40 try {
41 List<FileItem> items = upload.parseRequest(req);
42 for(FileItem item : items){
43 if(!item.isFormField()){
44 //文件名
45 String fileName = item.getName();
46 System.out.println(new String(fileName.getBytes(),"utf-8"));
47 fileName = new String(fileName.getBytes(),"utf-8");
48 //检查文件格式
49 String fileEnd = fileName.substring(fileName.lastIndexOf(".")+1).toLowerCase();
50 //真实上传路径
51 StringBuffer sbRealPath = new StringBuffer();
52 sbRealPath.append("D:/uploadFile/").append(fileName);
53 File file = new File(sbRealPath.toString());
54 item.write(file);
55 }
56 }
57 } catch (Exception e) {
58 e.printStackTrace();
59 }
60 }
61
62 }
过滤器：
package com.sgepit.ajax;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;
/**
* @author tengri
*跨域filter
*/
public class CrossDomainFilter implements Filter{
public void destroy() {
}
public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
throws IOException, ServletException {
HttpServletResponse res = (HttpServletResponse) resp;
//这里最好不要写通配符，如果允许多个域请求数据的话，可以直接用逗号隔开："http://www.baidu.com,http://google.com"
res.setHeader("Access-Control-Allow-Origin", "*");
res.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS");
res.setHeader("Access-Control-Allow-Headers", "Content-Type, Authorization, Accept,X-Requested-With");
chain.doFilter(req, resp);
}
public void init(FilterConfig arg0) throws ServletException {
}
}
web.xml配置过滤器：
1 <filter> 2 <filter-name>myFilter</filter-name> 3 <filter-class>com.sgepit.ajax.CrossDomainFilter</filter-class> 4 </filter> 5 <filter-mapping> 6 <filter-name>myFilter</filter-name> 7 <url-pattern>/*</url-pattern> 8 </filter-mapping>