用servlet进行文件的下载解决FF Cache和IE无法识别文件类型问题

为什么要用sevlet进行文件下载，而不是直接把url放在直接anchor里面：

<a href="setup.exe">download</a>

 

使用上面的方法遇到两个问题：

1.如果用户已经下载过文件，firefox会cache文件，用户再次进行下载时，会从cache里面下载，这样用户可能永远无法拿到最新的安装文件了，除非他清除浏览器的cache

 

2.尝试在url里面加入时间戳：<a href="setup.exe?time=<%=System.currentTimeMillis()">download</a>

FireFox 中问题解决，但是出现了一个新的问题：ie点击下载后，居然是未知类型的setup文件。

 

只好用个servlet下载了，对应servlet加入时间戳：

<ahref='downloadSetupApp.do?time=<%=System.currentTimeMillis()%>

 

Java文件如下：

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;


public class DownloadSetupAppAction extends BaseActionSupport {

    public static final Log sysLog = LogFactory
            .getLog(DownloadMiniAppAction.class);

    /**
     * **********************************************************************
     * This API is used to download the Setup.exe application.  Why need to
     * download the file using the servlet rather than directly add
     *  a link to the page:
     * 1.In FireFox, the file is always cached, thus the latest version
     * always download from the cache rather than from the site.  So the user
     * can not get the latest version when he has downloaded the applicaton
     *  before.
     *
     * 2.When add a time stamp to prevent cache by the browser, the IE can not
     * know the type of the application.  So user can not directly install it
     * directly
     *
     */
    public ActionForward execute(ActionMapping mapping, ActionForm actionForm,
            HttpServletRequest request, HttpServletResponse response) {
        String downloadPath = request.getScheme() + "://"
                + request.getServerName() + ":" + request.getServerPort()
                + request.getContextPath() + "/exe/setup.exe";
        response.setHeader("Pragma", "no-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0L);
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/force-download");

        OutputStream out = null;
        InputStream fileInputStream = null;
        try {
            String disHeader = "Attachment;Filename=\"setup.exe\"";
                   response.setHeader("Content-Disposition", disHeader);
                   out = response.getOutputStream();
            // transfer the file byte-by-byte to the response object
            URL url = new URL(downloadPath);
            URLConnection con = url.openConnection(); // *
            con.connect();
            fileInputStream = con.getInputStream();
            int i;
            while ((i = fileInputStream.read()) != -1) {
                out.write(i);
            }
        } catch (IOException e) {
            log.error(e, e);
        } catch(Exception e){
            log.error(e,e);
        }
        finally {
            try {
                if(fileInputStream!=null){
                    fileInputStream.close();
                }
                if(out!=null){
                    out.close();
                }
            } catch (IOException e) {
                log.error(e,e);
            }
        }
       
        return null;
    }

}