http断点续传java_用Java实现断点续传参考(HTTP)

断点续传的原理

其实断点续传的原理很简单&＃xff0c;就是在 Http 的请求上和一般的下载有所不同而已。        打个比方&＃xff0c;浏览器请求服务器上的一个文时&＃xff0c;所发出的请求如下&＃xff1a;        假设服务器域名为 wwww.sjtu.edu.cn&＃xff0c;文件名为 down.zip。 GET /down.zip HTTP/1.1         Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-         excel, application/msword, application/vnd.ms-powerpoint, */*         Accept-Language: zh-cn         Accept-Encoding: gzip, deflate         User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)         Connection: Keep-Alive

服务器收到请求后&＃xff0c;按要求寻找请求的文件&＃xff0c;提取文件的信息&＃xff0c;然后返回给浏览器&＃xff0c;返回信息如下&＃xff1a;

200         Content-Length&＃61;106786028         Accept-Ranges&＃61;bytes         Date&＃61;Mon, 30 Apr 2001 12:56:11 GMT         ETag&＃61;W/"02ca57e173c11:95b"        Content-Type&＃61;application/octet-stream         Server&＃61;Microsoft-IIS/5.0         Last-Modified&＃61;Mon, 30 Apr 2001 12:56:11 GMT

所谓断点续传&＃xff0c;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&＃xff0c;要求从 2000070 字节开始。        GET /down.zip HTTP/1.0         User-Agent: NetFox         RANGE: bytes&＃61;2000070-         Accept: text/html, image/gif, image/jpeg, *; q&＃61;.2, */*; q&＃61;.2

仔细看一下就会发现多了一行 RANGE: bytes&＃61;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&＃xff0c;前面的字节不用传了。        服务器收到这个请求以后&＃xff0c;返回的信息如下&＃xff1a;        206         Content-Length&＃61;106786028         Content-Range&＃61;bytes 2000070-106786027/106786028         Date&＃61;Mon, 30 Apr 2001 12:55:20 GMT         ETag&＃61;W/"02ca57e173c11:95b"        Content-Type&＃61;application/octet-stream         Server&＃61;Microsoft-IIS/5.0         Last-Modified&＃61;Mon, 30 Apr 2001 12:55:20 GMT

和前面服务器返回的信息比较一下&＃xff0c;就会发现增加了一行&＃xff1a;        Content-Range&＃61;bytes 2000070-106786027/106786028         返回的代码也改为 206 了&＃xff0c;而不再是 200 了。

知道了以上原理&＃xff0c;就可以进行断点续传的编程了。

Java 实现断点续传的关键几点

(1) 用什么方法实现提交 RANGE: bytes&＃61;2000070-。          当然用最原始的 Socket 是肯定能完成的&＃xff0c;不过那样太费事了&＃xff0c;其实 Java 的 net 包中提供了这种功能。代码如下&＃xff1a;

URL url &＃61; new URL("http://www.sjtu.edu.cn/down.zip");           HttpURLConnection httpConnection &＃61;  (HttpURLConnection)url.openConnection();

// 设置 User-Agent           httpConnection.setRequestProperty("User-Agent","NetFox");           // 设置断点续传的开始位置          httpConnection.setRequestProperty("RANGE","bytes&＃61;2000070");           // 获得输入流          InputStream input &＃61; 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&＃xff0c;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&＃xff0c;假设从 2000070 处开始保存文件&＃xff0c;代码如下&＃xff1a;          RandomAccess oSavedFile &＃61; new  RandomAccessFile("down.zip","rw");           long nPos &＃61; 2000070;           // 定位文件指针到 nPos 位置          oSavedFile.seek(nPos);           byte[] b &＃61; new byte[1024];           int nRead;           // 从输入流中读入字节流&＃xff0c;然后写到文件中          while((nRead&＃61;input.read(b,0,1024)) > 0)           {           oSavedFile.write(b,0,nRead);           }

怎么样&＃xff0c;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。

断点续传内核的实现

主要用了 6 个类&＃xff0c;包括一个测试类。        SiteFileFetch.java 负责整个文件的抓取&＃xff0c;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&＃xff0c;如文件保存的目录&＃xff0c;名字&＃xff0c;抓取文件的 URL 等。        Utility.java 工具类&＃xff0c;放一些简单的方法。        TestMethod.java 测试类。

下面是源程序&＃xff1a;

/*/*

* SiteFileFetch.java*/package NetFox;

import java.io.*;

import java.net.*;public classSiteFileFetch extends Thread {

SiteInfoBean siteInfoBean&＃61; null; //文件信息 Bean

long[] nStartPos; //开始位置

long[] nEndPos; //结束位置

FileSplitterFetch[] fileSplitterFetch; //子线程对象

long nFileLength; //文件长度

boolean bFirst &＃61; true; //是否第一次取文件

boolean bStop &＃61; 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

publicSiteFileFetch(SiteInfoBean bean) throws IOException

{

siteInfoBean&＃61;bean;//tmpFile &＃61; File.createTempFile ("zhong","1111",new File(bean.getSFilePath()));

tmpFile &＃61; new File(bean.getSFilePath()&＃43;File.separator &＃43; bean.getSFileName()&＃43;".info");if(tmpFile.exists ())

{

bFirst&＃61; false;

read_nPos();

}else{

nStartPos&＃61; new long[bean.getNSplitter()];

nEndPos&＃61; new long[bean.getNSplitter()];

}

}public voidrun()

{//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

try{if(bFirst)

{

nFileLength&＃61;getFileSize();if(nFileLength &＃61;&＃61; -1)

{

System.err.println("File Length is not known!");

}else if(nFileLength &＃61;&＃61; -2)

{

System.err.println("File is not access!");

}else{for(int i&＃61;0;i

{

nStartPos[i]&＃61; (long)(i*(nFileLength/nStartPos.length));

}for(int i&＃61;0;i

{

nEndPos[i]&＃61; nStartPos[i&＃43;1];

}

nEndPos[nEndPos.length-1] &＃61;nFileLength;

}

}//启动子线程

fileSplitterFetch &＃61; newFileSplitterFetch[nStartPos.length];for(int i&＃61;0;i

{

fileSplitterFetch[i]&＃61; newFileSplitterFetch(siteInfoBean.getSSiteURL(),

siteInfoBean.getSFilePath()&＃43; File.separator &＃43;siteInfoBean.getSFileName(),

nStartPos[i],nEndPos[i],i);

Utility.log("Thread" &＃43; i &＃43; ", nStartPos &＃61;" &＃43; nStartPos[i] &＃43; ", nEndPos &＃61;"

&＃43;nEndPos[i]);

fileSplitterFetch[i].start();

}//fileSplitterFetch[nPos.length-1] &＃61; new FileSplitterFetch(siteInfoBean.getSSiteURL(),

siteInfoBean.getSFilePath() &＃43;File.separator&＃43; siteInfoBean.getSFileName(),nPos[nPos.length-1],nFileLength,nPos.length-1);//Utility.log("Thread " &＃43;(nPos.length-1) &＃43; ",nStartPos &＃61; "&＃43;nPos[nPos.length-1]&＃43;",

nEndPos &＃61; "&＃43; nFileLength);

//fileSplitterFetch[nPos.length-1].start();//等待子线程结束//int count &＃61; 0;//是否结束 while 循环

boolean breakWhile &＃61; false;while(!bStop)

{

write_nPos();

Utility.sleep(500);

breakWhile&＃61; true;for(int i&＃61;0;i

{if(!fileSplitterFetch[i].bDownOver)

{

breakWhile&＃61; false;break;

}

}if(breakWhile)break;//count&＃43;&＃43;;//if(count>4)//siteStop();

}

System.err.println("文件下载结束&＃xff01;");

}catch(Exception e){e.printStackTrace ();}

}//获得文件长度

public longgetFileSize()

{int nFileLength &＃61; -1;try{

URL url&＃61; newURL(siteInfoBean.getSSiteURL());

HttpURLConnection httpConnection&＃61;(HttpURLConnection)url.openConnection ();

httpConnection.setRequestProperty("User-Agent","NetFox");int responseCode&＃61;httpConnection.getResponseCode();if(responseCode>&＃61;400)

{

processErrorCode(responseCode);return -2; //-2 represent access is error

}

String sHeader;for(int i&＃61;1;;i&＃43;&＃43;)

{//DataInputStream in &＃61; new DataInputStream(httpConnection.getInputStream ());//Utility.log(in.readLine());

sHeader&＃61;httpConnection.getHeaderFieldKey(i);if(sHeader!&＃61;null)

{if(sHeader.equals("Content-Length"))

{

nFileLength&＃61;Integer.parseInt(httpConnection.getHeaderField(sHeader));break;

}

}else

break;

}

}catch(IOException e){e.printStackTrace ();}catch(Exception e){e.printStackTrace ();}

Utility.log(nFileLength);returnnFileLength;

}//保存下载信息(文件指针位置)

private voidwrite_nPos()

{try{

output&＃61; new DataOutputStream(newFileOutputStream(tmpFile));

output.writeInt(nStartPos.length);for(int i&＃61;0;i

{//output.writeLong(nPos[i]);

output.writeLong(fileSplitterFetch[i].nStartPos);

output.writeLong(fileSplitterFetch[i].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 voidread_nPos()

{try{

DataInputStream input&＃61; new DataInputStream(newFileInputStream(tmpFile));int nCount &＃61;input.readInt();

nStartPos&＃61; new long[nCount];

nEndPos&＃61; new long[nCount];for(int i&＃61;0;i

{

nStartPos[i]&＃61;input.readLong();

nEndPos[i]&＃61;input.readLong();

}

input.close();

}catch(IOException e){e.printStackTrace ();}catch(Exception e){e.printStackTrace ();}

}private void processErrorCode(intnErrorCode)

{

System.err.println("Error Code :" &＃43;nErrorCode);

}//停止文件下载

public voidsiteStop()

{

bStop&＃61; true;for(int i&＃61;0;i

fileSplitterFetch[i].splitterStop();

}

}/***FileSplitterFetch.java*/package NetFox;

import java.io.*;

import java.net.*;public classFileSplitterFetch extends Thread {

String sURL;//File URL

long nStartPos; //File Snippet Start Position

long nEndPos; //File Snippet End Position

int nThreadID; //Thread&＃39;s ID

boolean bDownOver &＃61; false; //Downing is over

boolean bStop &＃61; false; //Stop identical

FileAccessI fileAccessI &＃61; null; //File Access interface

public FileSplitterFetch(String sURL,String sName,long nStart,long nEnd,intid)

throws IOException

{this.sURL &＃61;sURL;this.nStartPos &＃61;nStart;this.nEndPos &＃61;nEnd;

nThreadID&＃61;id;

fileAccessI&＃61; newFileAccessI(sName,nStartPos);

}public voidrun()

{while(nStartPos

{try{

URL url&＃61; newURL(sURL);

HttpURLConnection httpConnection&＃61;(HttpURLConnection)url.openConnection ();

httpConnection.setRequestProperty("User-Agent","NetFox");

String sProperty&＃61; "bytes&＃61;"&＃43;nStartPos&＃43;"-";

httpConnection.setRequestProperty("RANGE",sProperty);

Utility.log(sProperty);

InputStream input&＃61;httpConnection.getInputStream();//logResponseHead(httpConnection);

byte[] b &＃61; new byte[1024];intnRead;while((nRead&＃61;input.read(b,0,1024)) > 0 && nStartPos

{

nStartPos&＃43;&＃61; fileAccessI.write(b,0,nRead);//if(nThreadID &＃61;&＃61; 1)//Utility.log("nStartPos &＃61; " &＃43; nStartPos &＃43; ", nEndPos &＃61; " &＃43; nEndPos);

}

Utility.log("Thread" &＃43; nThreadID &＃43; "is over!");

bDownOver&＃61; true;//nPos &＃61; fileAccessI.write (b,0,nRead);

}catch(Exception e){e.printStackTrace ();}

}

}//打印回应的头信息

public voidlogResponseHead(HttpURLConnection con)

{for(int i&＃61;1;;i&＃43;&＃43;)

{

String header&＃61;con.getHeaderFieldKey(i);if(header!&＃61;null)//responseHeaders.put(header,httpConnection.getHeaderField(header));

Utility.log(header&＃43;":"&＃43;con.getHeaderField(header));else

break;

}

}public voidsplitterStop()

{

bStop&＃61; true;

}

}/***FileAccess.java*/package NetFox;

import java.io.*;public classFileAccessI implements Serializable{

RandomAccessFile oSavedFile;longnPos;publicFileAccessI() throws IOException

{this("",0);

}public FileAccessI(String sName,longnPos) throws IOException

{

oSavedFile&＃61; new RandomAccessFile(sName,"rw");this.nPos &＃61;nPos;

oSavedFile.seek(nPos);

}public synchronized int write(byte[] b,int nStart,intnLen)

{int n &＃61; -1;try{

oSavedFile.write(b,nStart,nLen);

n&＃61;nLen;

}catch(IOException e)

{

e.printStackTrace ();

}returnn;

}

}/***SiteInfoBean.java*/package NetFox;public classSiteInfoBean {private String sSiteURL; //Site&＃39;s URL

private String sFilePath; //Saved File&＃39;s Path

private String sFileName; //Saved File&＃39;s Name

private int nSplitter; //Count of Splited Downloading File

publicSiteInfoBean()

{//default value of nSplitter is 5

this("","","",5);

}public SiteInfoBean(String sURL,String sPath,String sName,intnSpiltter)

{

sSiteURL&＃61;sURL;

sFilePath&＃61;sPath;

sFileName&＃61;sName;this.nSplitter &＃61;nSpiltter;

}publicString getSSiteURL()

{returnsSiteURL;

}public voidsetSSiteURL(String value)

{

sSiteURL&＃61;value;

}publicString getSFilePath()

{returnsFilePath;

}public voidsetSFilePath(String value)

{

sFilePath&＃61;value;

}publicString getSFileName()

{returnsFileName;

}public voidsetSFileName(String value)

{

sFileName&＃61;value;

}public intgetNSplitter()

{returnnSplitter;

}public void setNSplitter(intnCount)

{

nSplitter&＃61;nCount;

}

}/***Utility.java*/package NetFox;public classUtility {publicUtility()

{

}public static void sleep(intnSecond)

{try{

Thread.sleep(nSecond);

}catch(Exception e)

{

e.printStackTrace ();

}

}public static voidlog(String sMsg)

{

System.err.println(sMsg);

}public static void log(intsMsg)

{

System.err.println(sMsg);

}

}/***TestMethod.java*/package NetFox;public classTestMethod {publicTestMethod()

{///xx/weblogic60b2_win.exe

try{

SiteInfoBean bean&＃61; new SiteInfoBean("http://localhost/xx/weblogic60b2_win.exe","L:\\temp","weblogic60b2_win.exe",5);//SiteInfoBean bean &＃61; new SiteInfoBean("http://localhost:8080/down.zip","L:\\temp",

"weblogic60b2_win.exe",5);

SiteFileFetch fileFetch&＃61; newSiteFileFetch(bean);

fileFetch.start();

}catch(Exception e){e.printStackTrace ();}

}public static voidmain(String[] args)

{newTestMethod();

}

}