用Java实现HTTP断点续传功能.docx

1、用Java实现HTTP断点续传功能用Java实现HTTP断点续传功能.2007年06月25日 星期一 16:13(一)断点续传的原理其实断点续传的原理很简单，就是在Http的请求上和一般的下载有所不同而已。打个比方，浏览器请求服务器上的一个文时，所发出的请求如下：假设服务器域名为，文件名为down.zip。GET /down.zip HTTP/1.1Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/msword, application/vnd.m

2、s-powerpoint, */*Accept-Language: zh-cnAccept-Encoding: gzip, deflateUser-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)Connection: Keep-Alive服务器收到请求后，按要求寻找请求的文件，提取文件的信息，然后返回给浏览器，返回信息如下200Content-Length=106786028Accept-Ranges=bytesDate=Mon, 30 Apr 2001 12:56:11 GMTETag=W/02ca57e173c11:95

3、bContent-Type=application/octet-streamServer=Microsoft-IIS/5.0Last-Modified=Mon, 30 Apr 2001 12:56:11 GMT所谓断点续传，也就是要从文件已经下载的地方开始继续下载。所以在客户端浏览器传给Web服务器的时候要多加一条信息-从哪里开始。下面是用自己编的一个浏览器来传递请求信息给Web服务器，要求从2000070字节开始。GET /down.zip HTTP/1.0User-Agent: NetFoxRANGE: bytes=2000070-Accept: text/html, image/gif,

4、 image/jpeg, *; q=.2, */*; q=.2仔细看一下就会发现多了一行RANGE: bytes=2000070-这一行的意思就是告诉服务器down.zip这个文件从2000070字节开始传，前面的字节不用传了。服务器收到这个请求以后，返回的信息如下：206Content-Length=106786028Content-Range=bytes 2000070-106786027/106786028Date=Mon, 30 Apr 2001 12:55:20 GMTETag=W/02ca57e173c11:95bContent-Type=application/octet-str

5、eamServer=Microsoft-IIS/5.0Last-Modified=Mon, 30 Apr 2001 12:55:20 GMT和前面服务器返回的信息比较一下，就会发现增加了一行：Content-Range=bytes 2000070-106786027/106786028返回的代码也改为206了，而不再是200了。知道了以上原理，就可以进行断点续传的编程了。(二)Java实现断点续传的关键几点 (1)用什么方法实现提交RANGE: bytes=2000070-。当然用最原始的Socket是肯定能完成的，不过那样太费事了，其实Java的net包中提供了这种功能。代码如下：URL u

6、rl = new URL(HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection();/设置User-AgenthttpConnection.setRequestProperty(User-Agent,NetFox);/设置断点续传的开始位置httpConnection.setRequestProperty(RANGE,bytes=2000070);/获得输入流InputStream input = httpConnection.getInputStream();从输入流中取出的字节流就是down.zip

7、文件从2000070开始的字节流。大家看，其实断点续传用Java实现起来还是很简单的吧。接下来要做的事就是怎么保存获得的流到文件中去了。保存文件采用的方法。我采用的是IO包中的RandAccessFile类。操作相当简单，假设从2000070处开始保存文件，代码如下：RandomAccess oSavedFile = new RandomAccessFile(down.zip,rw);long nPos = 2000070;/定位文件指针到nPos位置oSavedFile.seek(nPos);byte b = new byte1024;int nRead;/从输入流中读入字节流，然后写到文件

8、中while(nRead=input.read(b,0,1024) > 0)oSavedFile.write(b,0,nRead);怎么样，也很简单吧。接下来要做的就是整合成一个完整的程序了。包括一系列的线程控制等等。(三)断点续传内核的实现主要用了6个类，包括一个测试类。SiteFileFetch.java负责整个文件的抓取，控制内部线程(FileSplitterFetch类)。FileSplitterFetch.java负责部分文件的抓取。FileAccess.java负责文件的存储。SiteInfoBean.java要抓取的文件的信息，如文件保存的目录，名字，抓取文件的URL等。U

9、tility.java工具类，放一些简单的方法。TestMethod.java测试类。下面是源程序： /*SiteFileFetch.java*/package NetFox;import java.io.*;import .*;public class SiteFileFetch extends Thread SiteInfoBean siteInfoBean = null; /文件信息Beanlong nStartPos; /开始位置long nEndPos; /结束位置FileSplitterFetch fileSplitterFetch; /子线程对象long nFileLength;

10、 /文件长度boolean bFirst = true; /是否第一次取文件boolean bStop = false; /停止标志File tmpFile; /文件下载的临时信息DataOutputStream output; /输出到文件的输出流public SiteFileFetch(SiteInfoBean bean) throws IOExceptionsiteInfoBean = bean;/tmpFile = File.createTempFile (zhong,1111,new File(bean.getSFilePath();tmpFile = new File(bean.g

11、etSFilePath()+File.separator + bean.getSFileName()+.info);if(tmpFile.exists ()bFirst = false;read_nPos();elsenStartPos = new longbean.getNSplitter();nEndPos = new longbean.getNSplitter();public void run()/获得文件长度/分割文件/实例FileSplitterFetch/启动FileSplitterFetch线程/等待子线程返回tryif(bFirst)nFileLength = getFile

12、Size();if(nFileLength = -1)System.err.println(File Length is not known!);else if(nFileLength = -2)System.err.println(File is not access!);elsefor(int i=0;i<nStartPos.length;i+)nStartPosi = (long)(i*(nFileLength/nStartPos.length);for(int i=0;i<nEndPos.length-1;i+)nEndPosi = nStartPosi+1;nEndPos

13、nEndPos.length-1 = nFileLength;/启动子线程fileSplitterFetch = new FileSplitterFetchnStartPos.length;for(int i=0;i<nStartPos.length;i+)fileSplitterFetchi = new FileSplitterFetch(siteInfoBean.getSSiteURL(),siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(),nStartPosi,nEndPosi,i);

14、Utility.log(Thread + i + , nStartPos = + nStartPosi + , nEndPos = + nEndPosi);fileSplitterFetchi.start();/ fileSplitterFetchnPos.length-1 = new FileSplitterFetch(siteInfoBean.getSSiteURL(),siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(),nPosnPos.length-1,nFileLength,nPos.l

15、ength-1);/ Utility.log(Thread + (nPos.length-1) + , nStartPos = + nPosnPos.length-1 + ,nEndPos = + nFileLength);/ fileSplitterFetchnPos.length-1.start();/等待子线程结束/int count = 0;/是否结束while循环boolean breakWhile = false;while(!bStop)write_nPos();Utility.sleep(500);breakWhile = true;for(int i=0;i<nStar

16、tPos.length;i+)if(!fileSplitterFetchi.bDownOver)breakWhile = false;break;if(breakWhile)break;/count+;/if(count>4)/ siteStop();System.err.println(文件下载结束！);catch(Exception e)e.printStackTrace ();/获得文件长度public long getFileSize()int nFileLength = -1;tryURL url = new URL(siteInfoBean.getSSiteURL();Htt

17、pURLConnection httpConnection = (HttpURLConnection)url.openConnection ();httpConnection.setRequestProperty(User-Agent,NetFox);int responseCode=httpConnection.getResponseCode();if(responseCode>=400)processErrorCode(responseCode);return -2; /-2 represent access is errorString sHeader;for(int i=1;i+

18、)/DataInputStream in = new DataInputStream(httpConnection.getInputStream ();/Utility.log(in.readLine();sHeader=httpConnection.getHeaderFieldKey(i);if(sHeader!=null)if(sHeader.equals(Content-Length)nFileLength = Integer.parseInt(httpConnection.getHeaderField(sHeader);break;elsebreak;catch(IOException

19、 e)e.printStackTrace ();catch(Exception e)e.printStackTrace ();Utility.log(nFileLength);return nFileLength;/保存下载信息（文件指针位置）private void write_nPos()tryoutput = new DataOutputStream(new FileOutputStream(tmpFile);output.writeInt(nStartPos.length);for(int i=0;i<nStartPos.length;i+)/ output.writeLong(

20、nPosi);output.writeLong(fileSplitterFetchi.nStartPos);output.writeLong(fileSplitterFetchi.nEndPos);output.close();catch(IOException e)e.printStackTrace ();catch(Exception e)e.printStackTrace ();/读取保存的下载信息（文件指针位置）private void read_nPos()tryDataInputStream input = new DataInputStream(new FileInputStre

21、am(tmpFile);int nCount = input.readInt();nStartPos = new longnCount;nEndPos = new longnCount;for(int i=0;i<nStartPos.length;i+)nStartPosi = input.readLong();nEndPosi = input.readLong();input.close();catch(IOException e)e.printStackTrace ();catch(Exception e)e.printStackTrace ();private void proce

22、ssErrorCode(int nErrorCode)System.err.println(Error Code : + nErrorCode);/停止文件下载public void siteStop()bStop = true;for(int i=0;i<nStartPos.length;i+)fileSplitterFetchi.splitterStop();/*FileSplitterFetch.java*/package NetFox;import java.io.*;import .*;public class FileSplitterFetch extends Thread

23、String sURL; /File URLlong nStartPos; /File Snippet Start Positionlong nEndPos; /File Snippet End Positionint nThreadID; /Threads IDboolean bDownOver = false; /Downing is overboolean bStop = false; /Stop identicalFileAccessI fileAccessI = null; /File Access interfacepublic FileSplitterFetch(String s

24、URL,String sName,long nStart,long nEnd,int id) throws IOExceptionthis.sURL = sURL;this.nStartPos = nStart;this.nEndPos = nEnd;nThreadID = id;fileAccessI = new FileAccessI(sName,nStartPos);public void run()while(nStartPos < nEndPos & !bStop)tryURL url = new URL(sURL);HttpURLConnection httpConnecti

25、on = (HttpURLConnection)url.openConnection ();httpConnection.setRequestProperty(User-Agent,NetFox);String sProperty = bytes=+nStartPos+-;httpConnection.setRequestProperty(RANGE,sProperty);Utility.log(sProperty);InputStream input = httpConnection.getInputStream();/logResponseHead(httpConnection);byte

26、 b = new byte1024;int nRead;while(nRead=input.read(b,0,1024) > 0 & nStartPos < nEndPos & !bStop)nStartPos += fileAccessI.write(b,0,nRead);/if(nThreadID = 1)/ Utility.log(nStartPos = + nStartPos + , nEndPos = + nEndPos);Utility.log(Thread + nThreadID + is over!);bDownOver = true;/nPos = fileAcc

27、essI.write (b,0,nRead);catch(Exception e)e.printStackTrace ();/打印回应的头信息public void logResponseHead(HttpURLConnection con)for(int i=1;i+)String header=con.getHeaderFieldKey(i);if(header!=null)/responseHeaders.put(header,httpConnection.getHeaderField(header);Utility.log(header+ : +con.getHeaderField(h

28、eader);elsebreak;public void splitterStop()bStop = true;/*FileAccess.java*/package NetFox;import java.io.*;public class FileAccessI implements SerializableRandomAccessFile oSavedFile;long nPos;public FileAccessI() throws IOExceptionthis(,0);public FileAccessI(String sName,long nPos) throws IOExcepti

29、onoSavedFile = new RandomAccessFile(sName,rw);this.nPos = nPos;oSavedFile.seek(nPos);public synchronized int write(byte b,int nStart,int nLen)int n = -1;tryoSavedFile.write(b,nStart,nLen);n = nLen;catch(IOException e)e.printStackTrace ();return n;/*SiteInfoBean.java*/package NetFox;public class SiteInfoBean private String sSiteURL; /Sites URLprivate String sFilePath; /Saved Files Pathprivate String sFi