用Java实现HTTP断点续传功能

1、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.ms-powerpoint, */*Acc

2、ept-Language: zh-cnAccept-Encoding: gzip, deflateUser-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0Connection: 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/"02ca57e173c11:95b"Content-

3、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/g

4、if, 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/"02ca57e173c11:95b"Content-Type=applic

5、ation/octet-streamServer=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

6、能。代码如下:URL url = new URL("HttpURLConnection httpConnection = (HttpURLConnectionurl.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 i

7、nput = httpConnection.getInputStream(;从输入流中取出的字节流就是down.zip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

8、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,然后写到文件中while(nRead=input.read(b,0,1024 > 0oSavedFile.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

9、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。Utility.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

10、nEndPos; /结束位置FileSplitterFetch fileSplitterFetch; /子线程对象long nFileLength; /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.createTe

11、mpFile ("zhong","1111",new File(bean.getSFilePath(; tmpFile = new File(bean.getSFilePath(+File.separator + bean.getSFileName(+".info" if(tmpFile.exists (bFirst = false;read_nPos(;elsenStartPos = new longbean.getNSplitter(;nEndPos = new longbean.getNSplitter(;public void

12、 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(bFirstnFileLength = getFileSize(;if(nFileLength = -1System.err.println("File Length is not known!"else if(nFileLength = -2System.err.println("File is not access!"elsefor(int i=0;i<nStartPos.length;i+nStar

13、tPosi = (long(i*(nFileLength/nStartPos.length;for(int i=0;i<nEndPos.length-1;i+nEndPosi = nStartPosi+1;nEndPosnEndPos.length-1 = nFileLength;/启动子线程fileSplitterFetch = new FileSplitterFetchnStartPos.length;for(int i=0;i<nStartPos.length;i+fileSplitterFetchi = new FileSplitterFetch(siteInfoBean.

14、getSSiteURL(,siteInfoBean.getSFilePath( + File.separator + siteInfoBean.getSFileName(,nStartPosi,nEndPosi,i;Utility.log("Thread " + i + " , nStartPos = " + nStartPosi + ", nEndPos = " + nEndPosi; fileSplitterFetchi.start(;/ fileSplitterFetchnPos.length-1 = new FileSplit

15、terFetch(siteInfoBean.getSSiteURL(, siteInfoBean.getSFilePath( + File.separator + siteInfoBean.getSFileName(,nPosnPos.length-1,nFileLength,nPos.length-1;/ Utility.log("Thread " + (nPos.length-1 + " , nStartPos = " + nPosnPos.length-1 + ", nEndPos = " + nFileLength;/ fil

16、eSplitterFetchnPos.length-1.start(;/等待子线程结束/int count = 0;/是否结束while循环boolean breakWhile = false;while(!bStopwrite_nPos(;Utility.sleep(500;breakWhile = true;for(int i=0;i<nStartPos.length;i+if(!fileSplitterFetchi.bDownOverbreakWhile = false;break;if(breakWhilebreak;/count+;/if(count>4/ siteSto

17、p(;System.err.println("文件下载结束!"catch(Exception ee.printStackTrace (;/获得文件长度public long getFileSize(int nFileLength = -1;tryURL url = new URL(siteInfoBean.getSSiteURL(;HttpURLConnection httpConnection = (HttpURLConnectionurl.openConnection (; httpConnection.setRequestProperty("User-Age

18、nt","NetFox"int responseCode=httpConnection.getResponseCode(;if(responseCode>=400processErrorCode(responseCode;return -2; /-2 represent access is errorString sHeader;for(int i=1;i+/DataInputStream in = new DataInputStream(httpConnection.getInputStream (;/Utility.log(in.readLine(;sH

19、eader=httpConnection.getHeaderFieldKey(i;if(sHeader!=nullif(sHeader.equals("Content-Length"nFileLength = Integer.parseInt(httpConnection.getHeaderField(sHeader;break;elsebreak;catch(IOException ee.printStackTrace (;catch(Exception ee.printStackTrace (;Utility.log(nFileLength;return nFileLe

20、ngth;/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(nPosi;output.writeLong(fileSplitterFetchi.nStartPos;output.writeLong(fileSplitterFetchi.nEndPos;output.clos

21、e(;catch(IOException ee.printStackTrace (;catch(Exception ee.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 FileInputStream(tmpFile; int nCount = input.readInt(;nStartPos = new longnCount;nEndPos = new longnCount;for(int i=0;i<nStartPo

22、s.length;i+nStartPosi = input.readLong(;nEndPosi = input.readLong(;input.close(;catch(IOException ee.printStackTrace (;catch(Exception ee.printStackTrace (;private void processErrorCode(int nErrorCodeSystem.err.println("Error Code : " + nErrorCode;/停止文件下载public void siteStop(bStop = true;f

23、or(int i=0;i<nStartPos.length;i+fileSplitterFetchi.splitterStop(;/*FileSplitterFetch.java*/package NetFox;import java.io.*;import .*;public class FileSplitterFetch extends Thread String sURL; /File URLlong nStartPos; /File Snippet Start Positionlong nEndPos; /File Snippet End Positionint nThreadI

24、D; /Thread's IDboolean bDownOver = false; /Downing is overboolean bStop = false; /Stop identicalFileAccessI fileAccessI = null; /File Access interfacepublic FileSplitterFetch(String sURL,String sName,long nStart,long nEnd,int id throws IOExceptionthis.sURL = sURL;this.nStartPos = nStart;this.nEn

25、dPos = nEnd;nThreadID = id;fileAccessI = new FileAccessI(sName,nStartPos;public void run(while(nStartPos < nEndPos && !bStoptryURL url = new URL(sURL;HttpURLConnection httpConnection = (HttpURLConnectionurl.openConnection (; httpConnection.setRequestProperty("User-Agent","N

26、etFox"String sProperty = "bytes="+nStartPos+"-"httpConnection.setRequestProperty("RANGE",sProperty;Utility.log(sProperty;InputStream input = httpConnection.getInputStream(;/logResponseHead(httpConnection;byte b = new byte1024;int nRead;while(nRead=input.read(b,0,10

27、24 > 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 =

28、fileAccessI.write (b,0,nRead;catch(Exception ee.printStackTrace (;/打印回应的头信息public void logResponseHead(HttpURLConnection confor(int i=1;i+String header=con.getHeaderFieldKey(i;if(header!=null/responseHeaders.put(header,httpConnection.getHeaderField(header;Utility.log(header+" : "+con.getHe

29、aderField(header;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 nPo

30、s throws IOException oSavedFile = new RandomAccessFile(sName,"rw"this.nPos = nPos;oSavedFile.seek(nPos;public synchronized int write(byte b,int nStart,int nLenint n = -1;tryoSavedFile.write(b,nStart,nLen;n = nLen;catch(IOException ee.printStackTrace (;本资料由-大学生创业|创业|创业网 return n; /* *SiteIn

31、foBean.java */ package NetFox; public class SiteInfoBean private String sSiteURL; /Site's URL private String sFilePath; /Saved File's Path private String sFileName; /Saved File's Name private int nSplitter; /Count of Splited Downloading File public SiteInfoBean( /default value of nSplitt

32、er is 5 this("","","",5; public SiteInfoBean(String sURL,String sPath,String sName,int nSpiltter sSiteURL= sURL; sFilePath = sPath; sFileName = sName; this.nSplitter = nSpiltter; public String getSSiteURL( return sSiteURL; public void setSSiteURL(String value sSiteURL =

33、 value; 在线代理|网页代理|代理网页| 减肥药排行榜|淘宝最好的减肥药|什么减肥药效果最好|减肥瘦身药| 本资料由-大学生创业|创业|创业网 public String getSFilePath( return sFilePath; public void setSFilePath(String value sFilePath = value; public String getSFileName( return sFileName; public void setSFileName(String value sFileName = value; public int getNSplitte