本文实例讲述了Java编程实现服务器端支持断点续传的方法。分享给大家供大家参考，具体如下：
大家知道Tomcat之流对静态资源可以实现断点续传支持，但是如果是一个被控制的流，如有权限控制，或下载地址仅是个代理的时候，这时候需要自己实现断点续传的支持，小弟不才，这里提供基本断点续传[a-,-b,a-b]的简单实现，经验证，可支持迅雷7和火狐的多次断点续传。现贴出代码，大家共同分享：
Servlet
import java.io.BufferedOutputStream;import java.io.File;import java.io.IOException;import java.io.RandomAccessFile;import java.io.UnsupportedEncodingException;import java.net.URI;import java.net.URISyntaxException;import java.net.URLDecoder;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.bsteel.cloud.storage.servlet.base.BaseServlet;import com.bsteel.cloud.storage.utils.FileUtil;/** * 文件下载(支持断点续传【迅雷/快车/旋风/Firefox/Chrome】) * @author jdkleo * */public class FileIoServlet extends BaseServlet { private static final long serialVersionUID = 1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException{ download(request,response); } /** * 文件下载 * @param request * @param response * @throws UnsupportedEncodingException */ private void download(HttpServletRequest request,HttpServletResponse response) throws UnsupportedEncodingException { File downloadFile = getFile(request); long pos = FileUtil.headerSetting(downloadFile, request, response);// log.info("跳过"+pos); ServletOutputStream os = null; BufferedOutputStream out = null; RandomAccessFile raf = null; byte b[] = new byte[1024];//暂存容器 try { os = response.getOutputStream(); out = new BufferedOutputStream(os); raf = new RandomAccessFile(downloadFile, "r"); raf.seek(pos); try { int n = 0; while ((n = raf.read(b, 0, 1024)) != -1) { out.write(b, 0, n); } out.flush(); } catch(IOException ie) { } } catch (Exception e) { log.error(e.getMessage(), e); } finally { if (out != null) { try { out.close(); } catch (IOException e) { log.error(e.getMessage(), e); } } if (raf != null) { try { raf.close(); } catch (IOException e) { log.error(e.getMessage(), e); } } } } private File getFile(HttpServletRequest request) throws UnsupportedEncodingException { String uriStr = request.getParameter("uri"); if (null != uriStr){ uriStr = URLDecoder.decode(uriStr,"UTF-8"); if (uriStr.startsWith("file://")){ uriStr = uriStr.substring(7); return new File(uriStr); }else if (uriStr.startsWith("hbase://")){ try { return new File(new URI(uriStr)); } catch (URISyntaxException e) { log.error(e.getMessage(),e); } } } throw new RuntimeException("it's not a real uri"); }}Range支持
import java.io.File;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * 文件处理工具 * @author jdkleo * */public class FileUtil { /** * 断点续传支持 * @param file * @param request * @param response * @return 跳过多少字节 */ public static long headerSetting(File file,HttpServletRequest request, HttpServletResponse response) { long len = file.length();//文件长度 if ( null == request.getHeader("Range") ){ setResponse(new RangeSettings(len),file.getName(),response); return 0; } String range = request.getHeader("Range").replaceAll("bytes=", ""); RangeSettings settings = getSettings(len,range); setResponse(settings,file.getName(),response); return settings.getStart(); } private static void setResponse(RangeSettings settings,String fileName, HttpServletResponse response) { response.addHeader("Content-Disposition", "attachment; filename=/"" + IoUtil.toUtf8String(fileName) + "/""); response.setContentType( IoUtil.setContentType(fileName));// set the MIME type. if (!settings.isRange()) { response.addHeader("Content-Length", String.valueOf(settings.getTotalLength())); } else { long start = settings.getStart(); long end = settings.getEnd(); long contentLength = settings.getContentLength(); response.setStatus(javax.servlet.http.HttpServletResponse.SC_PARTIAL_CONTENT); response.addHeader("Content-Length", String.valueOf(contentLength)); String contentRange = new StringBuffer("bytes ").append(start).append("-").append(end).append("/").append(settings.getTotalLength()).toString(); response.setHeader("Content-Range", contentRange); } } private static RangeSettings getSettings(long len, String range) { long contentLength = 0; long start = 0; long end = 0; if (range.startsWith("-"))// -500，最后500个 { contentLength = Long.parseLong(range.substring(1));//要下载的量 end = len-1; start = len - contentLength; } else if (range.endsWith("-"))//从哪个开始 { start = Long.parseLong(range.replace("-", "")); end = len -1; contentLength = len - start; } else//从a到b { String[] se = range.split("-"); start = Long.parseLong(se[0]); end = Long.parseLong(se[1]); contentLength = end-start+1; } return new RangeSettings(start,end,contentLength,len); }}Range封装
public class RangeSettings{ private long start; private long end; private long contentLength; private long totalLength; private boolean range; public RangeSettings(){ super(); } public RangeSettings(long start, long end, long contentLength,long totalLength) { this.start = start; this.end = end; this.contentLength = contentLength; this.totalLength = totalLength; this.range = true; } public RangeSettings(long totalLength) { this.totalLength = totalLength; } public long getStart() { return start; } public void setStart(long start) { this.start = start; } public long getEnd() { return end; } public void setEnd(long end) { this.end = end; } public long getContentLength() { return contentLength; } public void setContentLength(long contentLength) { this.contentLength = contentLength; } public long getTotalLength() { return totalLength; } public void setTotalLength(long totalLength) { this.totalLength = totalLength; } public boolean isRange() { return range; }}IO流相关处理工具类
import java.io.InputStream;public class IoUtil { public static String setContentType(String returnFileName){ String contentType = "application/octet-stream"; if (returnFileName.lastIndexOf(".") < 0) return contentType; returnFileName = returnFileName.toLowerCase(); returnFileName = returnFileName.substring(returnFileName.lastIndexOf(".")+1); if (returnFileName.equals("html") || returnFileName.equals("htm") || returnFileName.equals("shtml")){ contentType = "text/html"; } else if (returnFileName.equals("css")){ contentType = "text/css"; } else if (returnFileName.equals("xml")){ contentType = "text/xml"; } else if (returnFileName.equals("gif")){ contentType = "image/gif"; } else if (returnFileName.equals("jpeg") || returnFileName.equals("jpg")){ contentType = "image/jpeg"; } else if (returnFileName.equals("js")){ contentType = "application/x-javascript"; } else if (returnFileName.equals("atom")){ contentType = "application/atom+xml"; } else if (returnFileName.equals("rss")){ contentType = "application/rss+xml"; } else if (returnFileName.equals("mml")){ contentType = "text/mathml"; } else if (returnFileName.equals("txt")){ contentType = "text/plain"; } else if (returnFileName.equals("jad")){ contentType = "text/vnd.sun.j2me.app-descriptor"; } else if (returnFileName.equals("wml")){ contentType = "text/vnd.wap.wml"; } else if (returnFileName.equals("htc")){ contentType = "text/x-component"; } else if (returnFileName.equals("png")){ contentType = "image/png"; } else if (returnFileName.equals("tif") || returnFileName.equals("tiff")){ contentType = "image/tiff"; } else if (returnFileName.equals("wbmp")){ contentType = "image/vnd.wap.wbmp"; } else if (returnFileName.equals("ico")){ contentType = "image/x-icon"; } else if (returnFileName.equals("jng")){ contentType = "image/x-jng"; } else if (returnFileName.equals("bmp")){ contentType = "image/x-ms-bmp"; } else if (returnFileName.equals("svg")){ contentType = "image/svg+xml"; } else if (returnFileName.equals("jar") || returnFileName.equals("var") || returnFileName.equals("ear")){ contentType = "application/java-archive"; } else if (returnFileName.equals("doc")){ contentType = "application/msword"; } else if (returnFileName.equals("pdf")){ contentType = "application/pdf"; } else if (returnFileName.equals("rtf")){ contentType = "application/rtf"; } else if (returnFileName.equals("xls")){ contentType = "application/vnd.ms-excel"; } else if (returnFileName.equals("ppt")){ contentType = "application/vnd.ms-powerpoint"; } else if (returnFileName.equals("7z")){ contentType = "application/x-7z-compressed"; } else if (returnFileName.equals("rar")){ contentType = "application/x-rar-compressed"; } else if (returnFileName.equals("swf")){ contentType = "application/x-shockwave-flash"; } else if (returnFileName.equals("rpm")){ contentType = "application/x-redhat-package-manager"; } else if (returnFileName.equals("der") || returnFileName.equals("pem") || returnFileName.equals("crt")){ contentType = "application/x-x509-ca-cert"; } else if (returnFileName.equals("xhtml")){ contentType = "application/xhtml+xml"; } else if (returnFileName.equals("zip")){ contentType = "application/zip"; } else if (returnFileName.equals("mid") || returnFileName.equals("midi") || returnFileName.equals("kar")){ contentType = "audio/midi"; } else if (returnFileName.equals("mp3")){ contentType = "audio/mpeg"; } else if (returnFileName.equals("ogg")){ contentType = "audio/ogg"; } else if (returnFileName.equals("m4a")){ contentType = "audio/x-m4a"; } else if (returnFileName.equals("ra")){ contentType = "audio/x-realaudio"; } else if (returnFileName.equals("3gpp") || returnFileName.equals("3gp")){ contentType = "video/3gpp"; } else if (returnFileName.equals("mp4") ){ contentType = "video/mp4"; } else if (returnFileName.equals("mpeg") || returnFileName.equals("mpg") ){ contentType = "video/mpeg"; } else if (returnFileName.equals("mov")){ contentType = "video/quicktime"; } else if (returnFileName.equals("flv")){ contentType = "video/x-flv"; } else if (returnFileName.equals("m4v")){ contentType = "video/x-m4v"; } else if (returnFileName.equals("mng")){ contentType = "video/x-mng"; } else if (returnFileName.equals("asx") || returnFileName.equals("asf")){ contentType = "video/x-ms-asf"; } else if (returnFileName.equals("wmv")){ contentType = "video/x-ms-wmv"; } else if (returnFileName.equals("avi")){ contentType = "video/x-msvideo"; } return contentType; } // UTF8转码 public static String toUtf8String(String s) { StringBuffer sb = new StringBuffer(); int len = s.toCharArray().length; for (int i = 0; i < len; i++) { char c = s.charAt(i); if (c >= 0 && c <= 255) { sb.append(c); } else { byte[] b; try { b = Character.toString(c).getBytes("utf-8"); } catch (Exception ex) { System.out.println(ex); b = new byte[0]; } for (int j = 0; j < b.length; j++) { int k = b[j]; if (k < 0) k += 256; sb.append("%" + Integer.toHexString(k).toUpperCase()); } } } String s_utf8 = sb.toString(); sb.delete(0, sb.length()); sb.setLength(0); sb = null; return s_utf8; } public static InputStream skipFully(InputStream in,long howMany)throws Exception{ long remainning = howMany; long len = 0; while(remainning>0){ len = in.skip(len); remainning -= len; } return in; }}注有些类比如IoUtil方法来自于CSDN的网友总结，另外此类还不支持多Range配置如[a-b,c-d,-e]等。
希望本文所述对大家Java程序设计有所帮助。