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本文介紹了一種利用 Java 來實ç¾(xià n)斷點續(xù)傳的方法。
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斷點續(xù)傳的原ç†
其實斷點續(xù)傳的原ç†å¾ˆç°¡å–®ï¼Œå°±æ˜¯åœ¨Http的請求上和一般的下載有所ä¸åŒè€Œå·²ã€‚
打個比方,ç€è¦½å™¨è«‹æ±‚æœå‹™(wù)器上的一個文時,所發(fÄ)出的請求如下:
å‡è¨(shè)æœå‹™(wù)器域å為wwww.sjtu.edu.cn,文件å為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
æœå‹™(wù)器收到請求åŽï¼ŒæŒ‰è¦æ±‚尋找請求的文件,æå–文件的信æ¯ï¼Œç„¶åŽè¿”回給ç€è¦½å™¨ï¼Œè¿”回信æ¯å¦‚下:
200
Content-Length=106786028
Accept-Ranges=bytes
Date=Mon, 30 Apr 2001 12:56:11 GMT
ETag=W/"02ca57e173c11:95b"
Content-Type=application/octet-stream
Server=Microsoft-IIS/5.0
Last-Modified=Mon, 30 Apr 2001 12:56:11 GMT
所謂斷點續(xù)傳,也就是è¦å¾žæ–‡ä»¶å·²ç¶“(jÄ«ng)下載的地方開始繼續(xù)下載。所以在客戶端ç€è¦½å™¨å‚³çµ¦ Webæœå‹™(wù)器的時候è¦å¤šåŠ 一æ¢ä¿¡æ¯--從哪里開始。
下é¢æ˜¯ç”¨è‡ªå·±ç·¨çš„一個"ç€è¦½å™¨"來傳éžè«‹æ±‚ä¿¡æ¯çµ¦Webæœå‹™(wù)器,è¦æ±‚從2000070å—節(jié)開始。
GET /down.zip HTTP/1.0
User-Agent: NetFox
RANGE: bytes=2000070-
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
仔細看一下就會發(fÄ)ç¾(xià n)多了一行RANGE: bytes=2000070-
這一行的æ„æ€å°±æ˜¯å‘Šè¨´æœå‹™(wù)器down.zip這個文件從2000070å—節(jié)開始傳,å‰é¢çš„å—節(jié)ä¸ç”¨å‚³äº†ã€‚
æœå‹™(wù)器收到這個請求以åŽï¼Œè¿”回的信æ¯å¦‚下:
206
Content-Length=106786028
Content-Range=bytes 2000070-106786027/106786028
Date=Mon, 30 Apr 2001 12:55:20 GMT
ETag=W/"02ca57e173c11:95b"
Content-Type=application/octet-stream
Server=Microsoft-IIS/5.0
Last-Modified=Mon, 30 Apr 2001 12:55:20 GMT
å’Œå‰é¢æœå‹™(wù)器返回的信æ¯æ¯”較一下,就會發(fÄ)ç¾(xià n)å¢žåŠ äº†ä¸€è¡Œï¼š
Content-Range=bytes 2000070-106786027/106786028
返回的代碼也改為206了,而ä¸å†æ˜¯200了。
知é“了以上原ç†ï¼Œå°±å¯ä»¥é€²è¡Œæ–·é»žçºŒ(xù)傳的編程了。
Java實ç¾(xià n)斷點續(xù)傳的關(guÄn)éµå¹¾é»ž
-
(1)用什么方法實ç¾(xià n)æ交RANGE: bytes=2000070-。
當然用最原始的Socket是肯定能完æˆçš„,ä¸éŽé‚£æ¨£å¤ªè²»äº‹äº†ï¼Œå…¶å¯¦Javaçš„net包ä¸æ供了這種功能。代碼如下:
URL url = new URL("http://www.sjtu.edu.cn/down.zip");
HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection();
//è¨(shè)ç½®User-Agent
httpConnection.setRequestProperty("User-Agent","NetFox");
//è¨(shè)置斷點續(xù)傳的開始ä½ç½®
httpConnection.setRequestProperty("RANGE","bytes=2000070");
//ç²å¾—輸入æµ
InputStream input = httpConnection.getInputStream();
從輸入æµä¸å–出的å—節(jié)æµå°±æ˜¯down.zip文件從2000070開始的å—節(jié)æµã€‚大家看,其實斷點續(xù)傳用Java實ç¾(xià n)起來還是很簡單的å§ã€‚接下來è¦åšçš„事就是怎么ä¿å˜ç²å¾—çš„æµåˆ°æ–‡ä»¶ä¸åŽ»äº†ã€‚
-
ä¿å˜æ–‡ä»¶é‡‡ç”¨çš„方法。
我采用的是IO包ä¸çš„RandAccessFile類。
æ“作相當簡單,å‡è¨(shè)從2000070處開始ä¿å˜æ–‡ä»¶ï¼Œä»£ç¢¼å¦‚下:
RandomAccess oSavedFile = new RandomAccessFile("down.zip","rw");
long nPos = 2000070;
//定ä½æ–‡ä»¶æŒ‡é‡åˆ°nPosä½ç½®
oSavedFile.seek(nPos);
byte[] b = new byte[1024];
int nRead;
//從輸入æµä¸è®€å…¥å—節(jié)æµï¼Œç„¶åŽå¯«åˆ°æ–‡ä»¶ä¸
while((nRead=input.read(b,0,1024)) > 0)
{
oSavedFile.write(b,0,nRead);
}
怎么樣,也很簡單å§ã€‚接下來è¦åšçš„就是整åˆæˆä¸€å€‹å®Œæ•´çš„程åºäº†ã€‚包括一系列的線程控制ç‰ç‰ã€‚
斷點續(xù)傳內(nèi)æ ¸çš„å¯¦ç¾(xià n)
主è¦ç”¨äº†6個類,包括一個測試類。
SiteFileFetch.javaè² è²¬æ•´å€‹æ–‡ä»¶çš„æŠ“å–,控制內(nèi)部線程(FileSplitterFetché¡ž)。
FileSplitterFetch.javaè² è²¬éƒ¨åˆ†æ–‡ä»¶çš„æŠ“å–。
FileAccess.javaè² è²¬æ–‡ä»¶çš„å˜å„²ã€‚
SiteInfoBean.javaè¦æŠ“å–的文件的信æ¯ï¼Œå¦‚文件ä¿å˜çš„目錄,åå—,抓å–文件的URLç‰ã€‚
Utility.java工具類,放一些簡單的方法。
TestMethod.java測試類。
下é¢æ˜¯æºç¨‹åºï¼š
/*
**SiteFileFetch.java
*/
package NetFox;
import java.io.*;
import java.net.*;
public class SiteFileFetch extends Thread {
SiteInfoBean siteInfoBean = null; //文件信æ¯Bean
long[] nStartPos; //開始ä½ç½®
long[] nEndPos; //çµ(jié)æŸä½ç½®
FileSplitterFetch[] fileSplitterFetch; //å線程å°è±¡
long nFileLength; //文件長度
boolean bFirst = true; //是å¦ç¬¬ä¸€æ¬¡å–文件
boolean bStop = false; //åœæ¢æ¨™å¿—
File tmpFile; //文件下載的臨時信æ¯
DataOutputStream output; //輸出到文件的輸出æµ
public SiteFileFetch(SiteInfoBean bean) throws IOException
{
siteInfoBean = bean;
//tmpFile = File.createTempFile ("zhong","1111",new File(bean.getSFilePath()));
tmpFile = new File(bean.getSFilePath()+File.separator + bean.getSFileName()+".info");
if(tmpFile.exists ())
{
bFirst = false;
read_nPos();
}
else
{
nStartPos = new long[bean.getNSplitter()];
nEndPos = new long[bean.getNSplitter()];
}
}
public void run()
{
//ç²å¾—文件長度
//分割文件
//實例FileSplitterFetch
//啟動FileSplitterFetch線程
//ç‰å¾…å線程返回
try{
if(bFirst)
{
nFileLength = getFileSize();
if(nFileLength == -1)
{
System.err.println("File Length is not known!");
}
else if(nFileLength == -2)
{
System.err.println("File is not access!");
}
else
{
for(int i=0;i<nStartPos.length;i++)
{
nStartPos[i] = (long)(i*(nFileLength/nStartPos.length));
}
for(int i=0;i<nEndPos.length-1;i++)
{
nEndPos[i] = nStartPos[i+1];
}
nEndPos[nEndPos.length-1] = nFileLength;
}
}
//å•Ÿå‹•å線程
fileSplitterFetch = new FileSplitterFetch[nStartPos.length];
for(int i=0;i<nStartPos.length;i++)
{
fileSplitterFetch[i] = new FileSplitterFetch(siteInfoBean.getSSiteURL(),
siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(),
nStartPos[i],nEndPos[i],i);
Utility.log("Thread " + i + " , nStartPos = " + nStartPos[i] + ", nEndPos = " + nEndPos[i]);
<!-- code sample is too wide -->fileSplitterFetch[i].start();
}
// fileSplitterFetch[nPos.length-1] = new FileSplitterFetch(siteInfoBean.getSSiteURL(),
siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(),nPos[nPos.length-1],nFileLength,nPos.length-1);
<!-- code sample is too wide -->// Utility.log("Thread " + (nPos.length-1) + " , nStartPos = " + nPos[nPos.length-1] + ",
nEndPos = " + nFileLength);
// fileSplitterFetch[nPos.length-1].start();
//ç‰å¾…å線程çµ(jié)æŸ
//int count = 0;
//是å¦çµ(jié)æŸwhile循環(huán)
boolean breakWhile = false;
while(!bStop)
{
write_nPos();
Utility.sleep(500);
breakWhile = true;
for(int i=0;i<nStartPos.length;i++)
{
if(!fileSplitterFetch[i].bDownOver)
{
breakWhile = false;
break;
}
}
if(breakWhile)
break;
//count++;
//if(count>4)
// siteStop();
}
System.err.println("文件下載çµ(jié)æŸï¼");
}
catch(Exception e){e.printStackTrace ();}
}
//ç²å¾—文件長度
public long getFileSize()
{
int nFileLength = -1;
try{
URL url = new URL(siteInfoBean.getSSiteURL());
HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection ();
httpConnection.setRequestProperty("User-Agent","NetFox");
int responseCode=httpConnection.getResponseCode();
if(responseCode>=400)
{
processErrorCode(responseCode);
return -2; //-2 represent access is error
}
String sHeader;
for(int i=1;;i++)
{
//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;
}
}
else
break;
}
}
catch(IOException e){e.printStackTrace ();}
catch(Exception e){e.printStackTrace ();}
Utility.log(nFileLength);
return nFileLength;
}
//ä¿å˜ä¸‹è¼‰ä¿¡æ¯ï¼ˆæ–‡ä»¶æŒ‡é‡ä½ç½®ï¼‰
private void write_nPos()
{
try{
output = new DataOutputStream(new FileOutputStream(tmpFile));
output.writeInt(nStartPos.length);
for(int i=0;i<nStartPos.length;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 ();}
}
//讀å–ä¿å˜çš„下載信æ¯ï¼ˆæ–‡ä»¶æŒ‡é‡ä½ç½®ï¼‰
private void read_nPos()
{
try{
DataInputStream input = new DataInputStream(new FileInputStream(tmpFile));
int nCount = input.readInt();
nStartPos = new long[nCount];
nEndPos = new long[nCount];
for(int i=0;i<nStartPos.length;i++)
{
nStartPos[i] = input.readLong();
nEndPos[i] = input.readLong();
}
input.close();
}
catch(IOException e){e.printStackTrace ();}
catch(Exception e){e.printStackTrace ();}
}
private void processErrorCode(int nErrorCode)
{
System.err.println("Error Code : " + nErrorCode);
}
//åœæ¢æ–‡ä»¶ä¸‹è¼‰
public void siteStop()
{
bStop = true;
for(int i=0;i<nStartPos.length;i++)
fileSplitterFetch[i].splitterStop();
}
}
/*
**FileSplitterFetch.java
*/
package NetFox;
import java.io.*;
import java.net.*;
public class FileSplitterFetch extends Thread {
String sURL; //File URL
long nStartPos; //File Snippet Start Position
long nEndPos; //File Snippet End Position
int nThreadID; //Thread's ID
boolean bDownOver = false; //Downing is over
boolean bStop = false; //Stop identical
FileAccessI fileAccessI = null; //File Access interface
public FileSplitterFetch(String sURL,String sName,long nStart,long nEnd,int id) throws IOException
<!-- code sample is too wide -->{
this.sURL = sURL;
this.nStartPos = nStart;
this.nEndPos = nEnd;
nThreadID = id;
fileAccessI = new FileAccessI(sName,nStartPos);
}
public void run()
{
while(nStartPos < nEndPos && !bStop)
{
try{
URL url = new URL(sURL);
HttpURLConnection httpConnection = (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[] b = new byte[1024];
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 = fileAccessI.write (b,0,nRead);
}
catch(Exception e){e.printStackTrace ();}
}
}
//打å°å›žæ‡‰çš„é ä¿¡æ¯
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(header));
else
break;
}
}
public void splitterStop()
{
bStop = true;
}
}
/*
**FileAccess.java
*/
package NetFox;
import java.io.*;
public class FileAccessI implements Serializable{
RandomAccessFile oSavedFile;
long nPos;
public FileAccessI() throws IOException
{
this("",0);
}
public FileAccessI(String sName,long nPos) throws IOException
{
oSavedFile = new RandomAccessFile(sName,"rw");
this.nPos = nPos;
oSavedFile.seek(nPos);
}
public synchronized int write(byte[] b,int nStart,int nLen)
{
int n = -1;
try{
oSavedFile.write(b,nStart,nLen);
n = nLen;
}
catch(IOException e)
{
e.printStackTrace ();
}
return n;
}
}
/*
**SiteInfoBean.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 nSplitter 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 = value;
}
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 getNSplitter()
{
return nSplitter;
}
public void setNSplitter(int nCount)
{
nSplitter = nCount;
}
}
/*
**Utility.java
*/
package NetFox;
public class Utility {
public Utility()
{
}
public static void sleep(int nSecond)
{
try{
Thread.sleep(nSecond);
}
catch(Exception e)
{
e.printStackTrace ();
}
}
public static void log(String sMsg)
{
System.err.println(sMsg);
}
public static void log(int sMsg)
{
System.err.println(sMsg);
}
}
/*
**TestMethod.java
*/
package NetFox;
public class TestMethod {
public TestMethod()
{ ///xx/weblogic60b2_win.exe
try{
SiteInfoBean bean = new SiteInfoBean("http://localhost/xx/weblogic60b2_win.exe","L:\\temp","weblogic60b2_win.exe",5);
<!-- code sample is too wide -->//SiteInfoBean bean = new SiteInfoBean("http://localhost:8080/down.zip","L:\\temp","weblogic60b2_win.exe",5);
<!-- code sample is too wide -->SiteFileFetch fileFetch = new SiteFileFetch(bean);
fileFetch.start();
}
catch(Exception e){e.printStackTrace ();}
}
public static void main(String[] args)
{
new TestMethod();
}
}
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