使文件下载的自定义连接支持 FlashGet 的断点续传多线程链接下载! JSP/Servlet 实现!

<%
/*
文件名可存为: Download.jsp
HTTP 协议的请求与响应的会话过程可通过使用 FlashGet 下载 Http:// 连接的过程监视:
蓝色部分为: 客户端请求
紫色部分为: 服务器端响应
如图:
http://blog.csdn.net/images/blog_csdn_net/playyuer/30110/o_FlashGet.gif
或参阅,后面的 FlashGet 会话列表:

*/
//你可以使用你服务器上的文件及其路径
String s = "I://SetupRes//Sun//j2re-1_4_2_05-windows-i586-p.exe";
//String s = "e://tree.mdb";

//经测试 RandomAccessFile 也可以实现,有兴趣可将注释去掉,并注释掉 FileInputStream 版本的语句
//java.io.RandomAccessFile raf = new java.io.RandomAccessFile(s,"r");

java.io.File f = new java.io.File(s);
java.io.FileInputStream fis = new java.io.FileInputStream(f);

response.reset();

response.setHeader("Server", "[e-mail] ");

//告诉客户端允许断点续传多线程连接下载
//响应的格式是:
//Accept-Ranges: bytes
response.setHeader("Accept-Ranges", "bytes");

long p = 0;
long l = 0;
//l = raf.length();
l = f.length();

//如果是第一次下,还没有断点续传,状态是默认的 200,无需显式设置
//响应的格式是:
//HTTP/1.1 200 OK

if (request.getHeader("Range") != null) //客户端请求的下载的文件块的开始字节
{
//如果是下载文件的范围而不是全部,向客户端声明支持并开始文件块下载
//要设置状态
//响应的格式是:
//HTTP/1.1 206 Partial Content
response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT);//206

//从请求中得到开始的字节
//请求的格式是:
//Range: bytes=[文件块的开始字节]-
p = Long.parseLong(request.getHeader("Range").replaceAll("bytes=","").replaceAll("-",""));
}

//下载的文件(或块)长度
//响应的格式是:
//Content-Length: [文件的总大小] - [客户端请求的下载的文件块的开始字节]
response.setHeader("Content-Length", new Long(l - p).toString());

if (p != 0)
{
//不是从最开始下载,
//响应的格式是:
//Content-Range: bytes [文件块的开始字节]-[文件的总大小 - 1]/[文件的总大小]
response.setHeader("Content-Range","bytes " + new Long(p).toString() + "-" + new Long(l -1).toString() + "/" + new Long(l).toString());
}

//response.setHeader("Connection", "Close"); //如果有此句话不能用 IE 直接下载

//使客户端直接下载
//响应的格式是:
//Content-Type: application/octet-stream
response.setContentType("application/octet-stream");

//为客户端下载指定默认的下载文件名称
//响应的格式是:
//Content-Disposition: attachment;filename="[文件名]"
//response.setHeader("Content-Disposition", "attachment;filename=/"" + s.substring(s.lastIndexOf("//") + 1) + "/""); //经测试 RandomAccessFile 也可以实现,有兴趣可将注释去掉,并注释掉 FileInputStream 版本的语句
response.setHeader("Content-Disposition", "attachment;filename=/"" + f.getName() + "/"");

//raf.seek(p);
fis.skip(p);

byte[] b = new byte[1024];
int i;

//while ( (i = raf.read(b)) != -1 ) //经测试 RandomAccessFile 也可以实现,有兴趣可将注释去掉,并注释掉 FileInputStream 版本的语句
while ( (i = fis.read(b)) != -1 )
{
response.getOutputStream().write(b,0,i);
}
//raf.close();//经测试 RandomAccessFile 也可以实现,有兴趣可将注释去掉,并注释掉 FileInputStream 版本的语句
fis.close();
%>

==========================================================================

在 FlashGet 中
一组第一次直接下载,还没有断点续传 HTTP 会话过程:
客户端请求:
Mon Aug 02 05:46:36 2004 正在连接 download2.flashfxp.com:80
Mon Aug 02 05:46:36 2004 正在连接 download2.flashfxp.com [IP=66.98.228.125:80]
Mon Aug 02 05:46:37 2004 已连接.
Mon Aug 02 05:46:37 2004 GET /zip/FlashFXP_30_Setup.exe HTTP/1.1
Mon Aug 02 05:46:37 2004 Host: download2.flashfxp.com
Mon Aug 02 05:46:37 2004 Accept: */*
Mon Aug 02 05:46:37 2004 Referer: http://playyuer.microshaoft.com
Mon Aug 02 05:46:37 2004 User-Agent: Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)
Mon Aug 02 05:46:37 2004 Pragma: no-cache
Mon Aug 02 05:46:37 2004 Cache-Control: no-cache
Mon Aug 02 05:46:37 2004 Authorization: Basic MGRheTpjY2ZfZG93bmxvYWQ=
Mon Aug 02 05:46:37 2004 Connection: close

服务器端响应:
Mon Aug 02 05:46:37 2004 HTTP/1.1 200 OK
Mon Aug 02 05:46:37 2004 Date: Sun, 01 Aug 2004 21:46:29 GMT
Mon Aug 02 05:46:37 2004 Server: Apache/1.3.27 (Unix) (Red-Hat/Linux) mod_fastcgi/2.2.12 mod_gzip/1.3.19.1a mod_jk/1.2.0 mod_perl/1.26 PHP/4.3.3 FrontPage/5.0.2 mod_ssl/2.8.12 OpenSSL/0.9.6b
Mon Aug 02 05:46:37 2004 Last-Modified: Fri, 30 Jul 2004 18:41:18 GMT
Mon Aug 02 05:46:37 2004 ETag: "4f80fa-1ecf20-410a964e"
Mon Aug 02 05:46:37 2004 Accept-Ranges: bytes
Mon Aug 02 05:46:37 2004 Content-Length: 2019104
Mon Aug 02 05:46:37 2004 Connection: close
Mon Aug 02 05:46:37 2004 Content-Type: application/octet-stream

一组断点续传的 HTTP 会话过程:
客户端请求:
Mon Aug 02 05:27:05 2004 正在连接 download2.flashfxp.com:80
Mon Aug 02 05:27:05 2004 正在连接 download2.flashfxp.com [IP=66.98.228.125:80]
Mon Aug 02 05:27:05 2004 已连接.
Mon Aug 02 05:27:05 2004 GET /zip/FlashFXP_30_Setup.exe HTTP/1.1
Mon Aug 02 05:27:05 2004 Host: download2.flashfxp.com
Mon Aug 02 05:27:05 2004 Accept: */*
Mon Aug 02 05:27:05 2004 Referer: http://playyuer.microshaoft.com
Mon Aug 02 05:27:05 2004 User-Agent: Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)
Mon Aug 02 05:27:05 2004 Range: bytes=191621-
Mon Aug 02 05:27:05 2004 Pragma: no-cache
Mon Aug 02 05:27:05 2004 Cache-Control: no-cache
Mon Aug 02 05:27:05 2004 Authorization: Basic MGRheTpjY2ZfZG93bmxvYWQ=
Mon Aug 02 05:27:05 2004 Connection: close

服务器端响应:
Mon Aug 02 05:27:06 2004 HTTP/1.1 206 Partial Content
Mon Aug 02 05:27:06 2004 Date: Sun, 01 Aug 2004 21:26:57 GMT
Mon Aug 02 05:27:06 2004 Server: Apache/1.3.27 (Unix) (Red-Hat/Linux) mod_fastcgi/2.2.12 mod_gzip/1.3.19.1a mod_jk/1.2.0 mod_perl/1.26 PHP/4.3.3 FrontPage/5.0.2 mod_ssl/2.8.12 OpenSSL/0.9.6b
Mon Aug 02 05:27:06 2004 Last-Modified: Fri, 30 Jul 2004 18:41:18 GMT
Mon Aug 02 05:27:06 2004 ETag: "4f80fa-1ecf20-410a964e"
Mon Aug 02 05:27:06 2004 Accept-Ranges: bytes
Mon Aug 02 05:27:06 2004 Content-Length: 1827483
Mon Aug 02 05:27:06 2004 Content-Range: bytes 191621-2019103/2019104
Mon Aug 02 05:27:06 2004 Connection: close
Mon Aug 02 05:27:06 2004 Content-Type: application/octet-stream