断点续传 (HTTP) 归纳

由于最近项目中要上传较大的文件，基于公司原有的底层框架的局限性，对于大文件的传输都束手无策，基于文件传输的安全性，考虑用断点续传(HTTP)以及FTP上传两种方式实现下面归纳下HTTP续传和FTP上传[FTP上传后续附上]

实现断点续传 (HTTP)

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 wwww.sjtu.edu.cn，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，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：

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/1.0 
User-Agent: NetFox 
RANGE: 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 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： 
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

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。

实现断点续传的关键几点：

1. (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-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。

2. 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。

SiteFileFetch.java 

 /*
  /*
  * 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 == -)
  {
  System.err.println("File Length is not known!");
  }
  else if(nFileLength == -)
  {
  System.err.println("File is not access!");
  }
  else
  {
  for(int i=;i<nStartPos.length;i++)
  {
  nStartPos[i] = (long)(i*(nFileLength/nStartPos.length));
  }
  for(int i=;i<nEndPos.length-;i++)
  {
  nEndPos[i] = nStartPos[i+];
  }
  nEndPos[nEndPos.length-] = nFileLength;
  }
  }
  // 启动子线程
  fileSplitterFetch = new FileSplitterFetch[nStartPos.length];
  for(int i=;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-],nFileLength,nPos.length-);
  // 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();
  breakWhile = true;
  for(int i=;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 = -;
  try{
  URL url = new URL(siteInfoBean.getSSiteURL());
  HttpURLConnection httpConnection = (HttpURLConnection)url.openConnection ();
  httpConnection.setRequestProperty("User-Agent","NetFox");
  int responseCode=httpConnection.getResponseCode();
  if(responseCode>=)
  {
  processErrorCode(responseCode);
  return -; //-2 represent access is error
  }
  String sHeader;
  for(int i=;;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=;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=;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=;i<nStartPos.length;i++)
  fileSplitterFetch[i].splitterStop();
  }
  }

FileSplitterFetch.java

 /*
  **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[];
  int nRead;
  while((nRead=input.read(b,,)) >  && nStartPos < nEndPos
  && !bStop)
  {
  nStartPos += fileAccessI.write(b,,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=;;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("",);
  }
  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 = -;
  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("","","",);
  }
  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",);
  //SiteInfoBean bean = new SiteInfoBean("http://localhost:8080/down.zip","L:\\temp",
      "weblogic60b2_win.exe",);
  SiteFileFetch fileFetch = new SiteFileFetch(bean);
  fileFetch.start();
  }
  catch(Exception e){e.printStackTrace ();}
  }
  public static void main(String[] args)
  {
  new TestMethod();
  }
  }