用Java实现断点续传(HTTP)
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Java实现断点续传的关键几点
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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-Agent
httpConnection.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。
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 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。
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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。
下面是源程序:
/***SiteFileFetch.java*/package NetFox;import java.io.*;import java.net.*;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; //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 = (long)(i*(nFileLength/nStartPos.length));}for(int i=0;i<nEndPos.length-1;i++){nEndPos = 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 = new FileSplitterFetch(siteInfoBean.getSSiteURL(),siteInfoBean.getSFilePath() + File.separator + siteInfoBean.getSFileName(),nStartPos,nEndPos,i);Utility.log("Thread " + i + " , nStartPos = " + nStartPos + ", nEndPos = " + nEndPos);fileSplitterFetch.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.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;}}elsebreak;}}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);output.writeLong(fileSplitterFetch.nStartPos);output.writeLong(fileSplitterFetch.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 = input.readLong();nEndPos = 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.splitterStop();}}/***FileSplitterFetch.java*/package NetFox;import java.io.*;import java.net.*;public class FileSplitterFetch extends Thread {String sURL; //File URLlong nStartPos; //File Snippet Start Positionlong nEndPos; //File Snippet End Positionint nThreadID; //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 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));elsebreak;}}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 URLprivate String sFilePath; //Saved File's Pathprivate String sFileName; //Saved File's Nameprivate int nSplitter; //Count of Splited Downloading Filepublic SiteInfoBean(){//default value of nSplitter is 5this("","","",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.exetry{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();}}[/pre]
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