远程下载

有针性的下载，实现strust文件下载，action控制如下：

/*
 * Generated by MyEclipse Struts
 * Template path: templates/java/JavaClass.vtl
 */
package org.topxp.struts;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.net.URLEncoder;

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

import org.apache.commons.io.IOUtils;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.actions.DispatchAction;

/** 
 * MyEclipse Struts
 * Creation date: 10-01-2007
 * 
 * XDoclet definition:
 * @struts.action
 * @struts.action-forward name="index" path="/resources/index.jsp"
 */
public class DownloadServerAction extends DispatchAction {

	@Override
	protected ActionForward unspecified(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception {
		
		//读取资源，并提供下载
		DownloadServerActionForm df = (DownloadServerActionForm)form;
		File root = new File("/");
		if(df.getName() != null && !df.getName().equals("")){
			root = new File(df.getName());
		}
		
		request.setAttribute("path", root.getPath());
		
		//提供下载
		if(root.isFile()){
			  java.io.File f = root;
			  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
			  String downloadname = URLEncoder.encode(f.getName());
			  response.setHeader("Content-Disposition", "attachment;filename=\"" + downloadname + "\"");

			  //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();
			
			
			
			
			
			
			return null;
		}else{
			File[] files = root.listFiles();
			if(root.getParentFile() != null){
				String parentPath = root.getParentFile().getPath();
				request.setAttribute("parent", parentPath);
			}else{
				request.setAttribute("parent", root.getPath());
			}
			
			request.setAttribute("files", files);
		}
		
		return mapping.findForward("index");
	}



}

jsp读取资源如下：

<%@ page language="java" contentType="text/html; charset=GB18030"
    pageEncoding="GB18030"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GB18030">
<title>Insert title here</title>
</head>
<body>
${path } 【<a href="resources.do?name=${parent }">返回</a>】
<hr>
<c:forEach items="${files}" var="file">
	<a href="resources.do?name=${file.path }">${file.name }</a> <br>
</c:forEach>
</body>
</html>