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用Java实现断点续传(HTTP)

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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wwww .sjtu.edu.cn,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, /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/"02ca57e173c11:95b"Content-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, 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200 0070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=application/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。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 url = new URL("http://www.sjtu.edu.cn/down.zip");HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection();//设置User- AgenthttpConnection.setRequestProperty("User-Agent","NetFox");//设置断点续传的开始位置htt pConnection.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RandAc cessFile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 byte[1024];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)) > 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。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。Utility.java工具类,放一些简单的方法。TestMethod.java测试类。代码来自 http://www.ibm.com/developerworks/cn/java/joy-down/index.html

SiteFileFetch.java

package NetFox;
import java.io.*;
import java.net.*;
public class SiteFileFetch extends Thread {
SiteInfoBean siteInfoBean = 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 = 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 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()
{
//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 = 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;
}
}
//启动子线程
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]);
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);
// Utility.log("Thread " + (nPos.length-1) + " , nStartPos = " + nPos[nPos.length-1] + ",
nEndPos = " + nFileLength);
// fileSplitterFetch[nPos.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<nStartPos.length;i++)
{
if(!fileSplitterFetch[i].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;
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;
}
//保存下载信息(文件指针位置)
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 ();}
}
//读取保存的下载信息(文件指针位置)
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);
}
//停止文件下载
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
{
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(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);
//SiteInfoBean bean = new SiteInfoBean("http://localhost:8080/down.zip","L:\\temp","weblogic60b2_win.exe",5);
SiteFileFetch fileFetch = new SiteFileFetch(bean);
fileFetch.start();
}
catch(Exception e){e.printStackTrace ();}
}
public static void main(String[] args)
{
new TestMethod();
}
}

标签:HTTP,断点续传,URLConnection,URL,HttpURLConnection

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