Java 多线程断点下载文件_详解

基本原理：利用URLConnection获取要下载文件的长度、头部等相关信息，并设置响应的头部信息。并且通过URLConnection获取输入流，将文件分成指定的块，每一块单独开辟一个线程完成数据的读取、写入。通过输入流读取下载文件的信息，然后将读取的信息用RandomAccessFile随机写入到本地文件中。同时，每个线程写入的数据都文件指针也就是写入数据的长度，需要保存在一个临时文件中。这样当本次下载没有完成的时候，下次下载的时候就从这个文件中读取上一次下载的文件长度，然后继续接着上一次的位置开始下载。并且将本次下载的长度写入到这个文件中。

个人博客：

http://hoojo.cnblogs.com

http://blog.csdn.net/IBM_hoojo

email: hoojo_@126.com

 

一、下载文件信息类、实体

封装即将下载资源的信息

        this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName;          this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath;          this.splitter = (splitter 1) ? SPLITTER_NUM : splitter;      }            /**      * b function: /b 通过url获得文件名称      * @author hoojo      * @createDate 2011-9-30 下午05:00:00      * @param url      * @return      */      private String getFileName(String url) {          return url.substring(url.lastIndexOf("/") + 1, url.length());      }            public String getUrl() {          return url;      }      public void setUrl(String url) {          if (url == null || "".equals(url)) {              throw new RuntimeException("url is not null!");          }          this.url = url;      }      public String getFileName() {          return fileName;      }      public void setFileName(String fileName) {          this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName;      }      public String getFilePath() {          return filePath;      }      public void setFilePath(String filePath) {          this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath;      }      public int getSplitter() {          return splitter;      }      public void setSplitter(int splitter) {          this.splitter = (splitter 1) ? SPLITTER_NUM : splitter;      }            @Override      public String toString() {          return this.url + "#" + this.fileName + "#" + this.filePath + "#" + this.splitter;      } 
public DownloadInfo(String url, String fileName, String filePath, int splitter) { super(); if (url == null || "".equals(url)) { throw new RuntimeException("url is not null!"); this.url = url; this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName; this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath; this.splitter = (splitter 1) ? SPLITTER_NUM : splitter; * b function: /b 通过url获得文件名称 * @author hoojo * @createDate 2011-9-30 下午05:00:00 * @param url * @return private String getFileName(String url) { return url.substring(url.lastIndexOf("/") + 1, url.length()); public String getUrl() { return url; public void setUrl(String url) { if (url == null || "".equals(url)) { throw new RuntimeException("url is not null!"); this.url = url; public String getFileName() { return fileName; public void setFileName(String fileName) { this.fileName = (fileName == null || "".equals(fileName)) ? getFileName(url) : fileName; public String getFilePath() { return filePath; public void setFilePath(String filePath) { this.filePath = (filePath == null || "".equals(filePath)) ? FILE_PATH : filePath; public int getSplitter() { return splitter; public void setSplitter(int splitter) { this.splitter = (splitter 1) ? SPLITTER_NUM : splitter; @Override public String toString() { return this.url + "#" + this.fileName + "#" + this.filePath + "#" + this.splitter;

 

二、随机写入一段文件
public SaveItemFile(String name, long pos) throws IOException { itemFile = new RandomAccessFile(name, "rw"); //在指定的pos位置开始写入数据 itemFile.seek(pos); * b function: /b 同步方法写入文件 * @author hoojo * @createDate 2011-9-26 下午12:21:22 * @param buff 缓冲数组 * @param start 起始位置 * @param length 长度 * @return public synchronized int write(byte[] buff, int start, int length) { int i = -1; try { itemFile.write(buff, start, length); i = length; } catch (IOException e) { e.printStackTrace(); return i; public void close() throws IOException { if (itemFile != null) { itemFile.close(); } 这个类主要是完成向本地的指定文件指针出开始写入文件，并返回当前写入文件的长度（文件指针）。这个类将被线程调用，文件被分成对应的块后，将被线程调用。每个线程都将会调用这个类完成文件的随机写入。

三、单个线程下载文件

                LogUtils.log("#start#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos);                  while ((length = is.read(buff)) 0 startPos endPos !isDownloadOver) {                      //写入文件内容，返回最后写入的长度                      startPos += itemFile.write(buff, 0, length);                  }                  LogUtils.log("#over#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos);                  LogUtils.log("Thread " + threadId + " is execute over!");                  this.isDownloadOver = true;              } catch (MalformedURLException e) {                  e.printStackTrace();              } catch (IOException e) {                  e.printStackTrace();              } finally {                  try {                      if (itemFile != null) {                          itemFile.close();                      }                  } catch (IOException e) {                      e.printStackTrace();                  }              }          }          if (endPos startPos !isDownloadOver) {              LogUtils.log("Thread " + threadId  + " startPos endPos, not need download file !");              this.isDownloadOver = true;          }          if (endPos == startPos !isDownloadOver) {              LogUtils.log("Thread " + threadId  + " startPos = endPos, not need download file !");              this.isDownloadOver = true;          }      }            /**      * b function: /b 打印下载文件头部信息      * @author hoojo      * @createDate 2011-9-22 下午05:44:35      * @param conn HttpURLConnection      */      public static void printHeader(URLConnection conn) {          int i = 1;          while (true) {              String header = conn.getHeaderFieldKey(i);              i++;              if (header != null) {                  LogUtils.info(header + ":" + conn.getHeaderField(i));              } else {                  break;              }          }      }            /**      * b function: /b 设置URLConnection的头部信息，伪装请求信息      * @author hoojo      * @createDate 2011-9-28 下午05:29:43      * @param con      */      public static void setHeader(URLConnection conn) {          conn.setRequestProperty("User-Agent", "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3");          conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3");          conn.setRequestProperty("Accept-Encoding", "utf-8");          conn.setRequestProperty("Accept-Charset", "ISO-8859-1,utf-8;q=0.7,*;q=0.7");          conn.setRequestProperty("Keep-Alive", "300");          conn.setRequestProperty("connnection", "keep-alive");          conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT");          conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\"");          conn.setRequestProperty("Cache-conntrol", "max-age=0");          conn.setRequestProperty("Referer", "http://www.baidu.com");      }            public boolean isDownloadOver() {          return isDownloadOver;      }            public long getStartPos() {          return startPos;      }      public long getEndPos() {          return endPos;      } 
public DownloadFile(String url, String name, long startPos, long endPos, int threadId) throws IOException { super(); this.url = url; this.startPos = startPos; this.endPos = endPos; this.threadId = threadId; //分块下载写入文件内容 this.itemFile = new SaveItemFile(name, startPos);
URL url = new URL(this.url); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); // 设置连接超时时间为10000ms conn.setConnectTimeout(10000); // 设置读取数据超时时间为10000ms conn.setReadTimeout(10000); setHeader(conn); String property = "bytes=" + startPos + "-"; conn.setRequestProperty("RANGE", property); //输出log信息 LogUtils.log("开始 " + threadId + "：" + property + endPos); //printHeader(conn); //获取文件输入流，读取文件内容 InputStream is = conn.getInputStream(); byte[] buff = new byte[BUFF_LENGTH]; int length = -1; LogUtils.log("#start#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos); while ((length = is.read(buff)) 0 startPos endPos !isDownloadOver) { //写入文件内容，返回最后写入的长度 startPos += itemFile.write(buff, 0, length); LogUtils.log("#over#Thread: " + threadId + ", startPos: " + startPos + ", endPos: " + endPos); LogUtils.log("Thread " + threadId + " is execute over!"); this.isDownloadOver = true; } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (itemFile != null) { itemFile.close(); } catch (IOException e) { e.printStackTrace(); if (endPos startPos !isDownloadOver) { LogUtils.log("Thread " + threadId + " startPos endPos, not need download file !"); this.isDownloadOver = true; if (endPos == startPos !isDownloadOver) { LogUtils.log("Thread " + threadId + " startPos = endPos, not need download file !"); this.isDownloadOver = true; * b function: /b 打印下载文件头部信息 * @author hoojo * @createDate 2011-9-22 下午05:44:35 * @param conn HttpURLConnection public static void printHeader(URLConnection conn) { int i = 1; while (true) { String header = conn.getHeaderFieldKey(i); i++; if (header != null) { LogUtils.info(header + ":" + conn.getHeaderField(i)); } else { break; * b function: /b 设置URLConnection的头部信息，伪装请求信息 * @author hoojo * @createDate 2011-9-28 下午05:29:43 * @param con public static void setHeader(URLConnection conn) { conn.setRequestProperty("User-Agent", "Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008092510 Ubuntu/8.04 (hardy) Firefox/3.0.3"); conn.setRequestProperty("Accept-Language", "en-us,en;q=0.7,zh-cn;q=0.3"); conn.setRequestProperty("Accept-Encoding", "utf-8"); conn.setRequestProperty("Accept-Charset", "ISO-8859-1,utf-8;q=0.7,*;q=0.7"); conn.setRequestProperty("Keep-Alive", "300"); conn.setRequestProperty("connnection", "keep-alive"); conn.setRequestProperty("If-Modified-Since", "Fri, 02 Jan 2009 17:00:05 GMT"); conn.setRequestProperty("If-None-Match", "\"1261d8-4290-df64d224\""); conn.setRequestProperty("Cache-conntrol", "max-age=0"); conn.setRequestProperty("Referer", "http://www.baidu.com"); public boolean isDownloadOver() { return isDownloadOver; public long getStartPos() { return startPos; public long getEndPos() { return endPos; } 这个类主要是完成单个线程的文件下载，将通过URLConnection读取指定url的资源信息。然后用InputStream读取文件内容，然后调用调用SaveItemFile类，向本地写入当前要读取的块的内容。

 

四、分段多线程写入文件内容

        String tempPath = this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName() + ".position";          tempFile = new File(tempPath);          //如果存在读入点位置的文件          if (tempFile.exists()) {              first = false;              //就直接读取内容              try {                  readPosInfo();              } catch (IOException e) {                  e.printStackTrace();              }          } else {              //数组的长度就要分成多少段的数量              startPos = new long[downloadInfo.getSplitter()];              endPos = new long[downloadInfo.getSplitter()];          }      }            @Override      public void run() {          //首次下载，获取下载文件长度          if (first) {              length = this.getFileSize();//获取文件长度              if (length == -1) {                  LogUtils.log("file length is know!");                  stop = true;              } else if (length == -2) {                  LogUtils.log("read file length is error!");                  stop = true;              } else if (length 0) {                  /**                  * eg                  * start: 1, 3, 5, 7, 9                  * end: 3, 5, 7, 9, length                  */                  for (int i = 0, len = startPos.length; i len; i++) {                      int size = i * (length / len);                      startPos[i] = size;                                            //设置最后一个结束点的位置                      if (i == len - 1) {                          endPos[i] = length;                      } else {                          size = (i + 1) * (length / len);                          endPos[i] = size;                      }                      LogUtils.log("start-end Position[" + i + "]: " + startPos[i] + "-" + endPos[i]);                  }              } else {                  LogUtils.log("get file length is error, download is stop!");                  stop = true;              }          }                    //子线程开始下载          if (!stop) {              //创建单线程下载对象数组              fileItem = new DownloadFile[startPos.length];//startPos.length = downloadInfo.getSplitter()              for (int i = 0; i startPos.length; i++) {                  try {                      //创建指定个数单线程下载对象，每个线程独立完成指定块内容的下载                      fileItem[i] = new DownloadFile(                          downloadInfo.getUrl(),                           this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName(),                           startPos[i], endPos[i], i                      );                      fileItem[i].start();//启动线程，开始下载                      LogUtils.log("Thread: " + i + ", startPos: " + startPos[i] + ", endPos: " + endPos[i]);                  } catch (IOException e) {                      e.printStackTrace();                  }              }                            //循环写入下载文件长度信息              while (!stop) {                  try {                      writePosInfo();                      LogUtils.log("downloading……");                      Thread.sleep(SLEEP_SECONDS);                      stop = true;                  } catch (IOException e) {                      e.printStackTrace();                  } catch (InterruptedException e) {                      e.printStackTrace();                  }                  for (int i = 0; i startPos.length; i++) {                      if (!fileItem[i].isDownloadOver()) {                          stop = false;                          break;                      }                  }              }              LogUtils.info("Download task is finished!");          }      }            /**      * 将写入点数据保存在临时文件中      * @author hoojo      * @createDate 2011-9-23 下午05:25:37      * @throws IOException      */      private void writePosInfo() throws IOException {          DataOutputStream dos = new DataOutputStream(new FileOutputStream(tempFile));          dos.writeInt(startPos.length);          for (int i = 0; i startPos.length; i++) {              dos.writeLong(fileItem[i].getStartPos());              dos.writeLong(fileItem[i].getEndPos());              //LogUtils.info("[" + fileItem[i].getStartPos() + "#" + fileItem[i].getEndPos() + "]");          }          dos.close();      }            /**      * b function: /b 读取写入点的位置信息      * @author hoojo      * @createDate 2011-9-23 下午05:30:29
throws IOException {          DataInputStream dis = new DataInputStream(new FileInputStream(tempFile));          int startPosLength = dis.readInt();          startPos = new long[startPosLength];          endPos = new long[startPosLength];          for (int i = 0; i startPosLength; i++) {              startPos[i] = dis.readLong();              endPos[i] = dis.readLong();          }          dis.close();      }            /**      * b function: /b 获取下载文件的长度      * @author hoojo      * @createDate 2011-9-26 下午12:15:08      * @return      */      private int getFileSize() {          int fileLength = -1;          try {              URL url = new URL(this.downloadInfo.getUrl());              HttpURLConnection conn = (HttpURLConnection) url.openConnection();                            DownloadFile.setHeader(conn);              int stateCode = conn.getResponseCode();              //判断http status是否为HTTP/1.1 206 Partial Content或者200 OK              if (stateCode != HttpURLConnection.HTTP_OK stateCode != HttpURLConnection.HTTP_PARTIAL) {                  LogUtils.log("Error Code: " + stateCode);                  return -2;              } else if (stateCode = 400) {                  LogUtils.log("Error Code: " + stateCode);                  return -2;              } else {                  //获取长度                  fileLength = conn.getContentLength();                  LogUtils.log("FileLength: " + fileLength);              }                            //读取文件长度 
            DownloadFile.printHeader(conn);          } catch (MalformedURLException e) {              e.printStackTrace();          } catch (IOException e) {              e.printStackTrace();          }          return fileLength;      } 
public BatchDownloadFile(DownloadInfo downloadInfo) { this.downloadInfo = downloadInfo; String tempPath = this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName() + ".position"; tempFile = new File(tempPath); //如果存在读入点位置的文件 if (tempFile.exists()) { first = false; //就直接读取内容 try { readPosInfo(); } catch (IOException e) { e.printStackTrace(); } else { //数组的长度就要分成多少段的数量 startPos = new long[downloadInfo.getSplitter()]; endPos = new long[downloadInfo.getSplitter()]; @Override public void run() { //首次下载，获取下载文件长度 if (first) { length = this.getFileSize();//获取文件长度 if (length == -1) { LogUtils.log("file length is know!"); stop = true; } else if (length == -2) { LogUtils.log("read file length is error!"); stop = true; } else if (length 0) { * eg * start: 1, 3, 5, 7, 9 * end: 3, 5, 7, 9, length for (int i = 0, len = startPos.length; i len; i++) { int size = i * (length / len); startPos[i] = size; //设置最后一个结束点的位置 if (i == len - 1) { endPos[i] = length; } else { size = (i + 1) * (length / len); endPos[i] = size; LogUtils.log("start-end Position[" + i + "]: " + startPos[i] + "-" + endPos[i]); } else { LogUtils.log("get file length is error, download is stop!"); stop = true; //子线程开始下载 if (!stop) { //创建单线程下载对象数组 fileItem = new DownloadFile[startPos.length];//startPos.length = downloadInfo.getSplitter() for (int i = 0; i startPos.length; i++) { try { //创建指定个数单线程下载对象，每个线程独立完成指定块内容的下载 fileItem[i] = new DownloadFile( downloadInfo.getUrl(), this.downloadInfo.getFilePath() + File.separator + downloadInfo.getFileName(), startPos[i], endPos[i], i fileItem[i].start();//启动线程，开始下载 LogUtils.log("Thread: " + i + ", startPos: " + startPos[i] + ", endPos: " + endPos[i]); } catch (IOException e) { e.printStackTrace(); //循环写入下载文件长度信息 while (!stop) { try { writePosInfo(); LogUtils.log("downloading……"); Thread.sleep(SLEEP_SECONDS); stop = true; } catch (IOException e) { e.printStackTrace(); } catch (InterruptedException e) { e.printStackTrace(); for (int i = 0; i startPos.length; i++) { if (!fileItem[i].isDownloadOver()) { stop = false; break; LogUtils.info("Download task is finished!"); * 将写入点数据保存在临时文件中 * @author hoojo * @createDate 2011-9-23 下午05:25:37 * @throws IOException private void writePosInfo() throws IOException { DataOutputStream dos = new DataOutputStream(new FileOutputStream(tempFile)); dos.writeInt(startPos.length); for (int i = 0; i startPos.length; i++) { dos.writeLong(fileItem[i].getStartPos()); dos.writeLong(fileItem[i].getEndPos()); //LogUtils.info("[" + fileItem[i].getStartPos() + "#" + fileItem[i].getEndPos() + "]"); dos.close(); * b function: /b 读取写入点的位置信息 * @author hoojo * @createDate 2011-9-23 下午05:30:29 * @throws IOException private void readPosInfo() throws IOException { DataInputStream dis = new DataInputStream(new FileInputStream(tempFile)); int startPosLength = dis.readInt(); startPos = new long[startPosLength]; endPos = new long[startPosLength]; for (int i = 0; i startPosLength; i++) { startPos[i] = dis.readLong(); endPos[i] = dis.readLong(); dis.close(); * b function: /b 获取下载文件的长度 * @author hoojo * @createDate 2011-9-26 下午12:15:08 * @return private int getFileSize() { int fileLength = -1; try { URL url = new URL(this.downloadInfo.getUrl()); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); DownloadFile.setHeader(conn); int stateCode = conn.getResponseCode(); //判断http status是否为HTTP/1.1 206 Partial Content或者200 OK if (stateCode != HttpURLConnection.HTTP_OK stateCode != HttpURLConnection.HTTP_PARTIAL) { LogUtils.log("Error Code: " + stateCode); return -2; } else if (stateCode = 400) { LogUtils.log("Error Code: " + stateCode); return -2; } else { //获取长度 fileLength = conn.getContentLength(); LogUtils.log("FileLength: " + fileLength); //读取文件长度 /*for (int i = 1; ; i++) { String header = conn.getHeaderFieldKey(i); if (header != null) { if ("Content-Length".equals(header)) { fileLength = Integer.parseInt(conn.getHeaderField(i)); break; } else { break; DownloadFile.printHeader(conn); } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); return fileLength; }这个类主要是完成读取指定url资源的内容，获取该资源的长度。然后将该资源分成指定的块数，将每块的起始下载位置、结束下载位置，分别保存在一个数组中。每块都单独开辟一个独立线程开始下载。在开始下载之前，需要创建一个临时文件，写入当前下载线程的开始下载指针位置和结束下载指针位置。

 

五、工具类、测试类

日志工具类

        LogUtils.info(bean);          BatchDownloadFile down = new BatchDownloadFile(bean);          new Thread(down).start();      }            public static void download(String url, int threadNum) {          DownloadInfo bean = new DownloadInfo(url, threadNum);          LogUtils.info(bean);          BatchDownloadFile down = new BatchDownloadFile(bean);          new Thread(down).start();      }            public static void download(String url, String fileName, String filePath, int threadNum) {          DownloadInfo bean = new DownloadInfo(url, fileName, filePath, threadNum);          LogUtils.info(bean);          BatchDownloadFile down = new BatchDownloadFile(bean);          new Thread(down).start();      } 
public static void download(String url, int threadNum) { DownloadInfo bean = new DownloadInfo(url, threadNum); LogUtils.info(bean); BatchDownloadFile down = new BatchDownloadFile(bean); new Thread(down).start(); public static void download(String url, String fileName, String filePath, int threadNum) { DownloadInfo bean = new DownloadInfo(url, fileName, filePath, threadNum); LogUtils.info(bean); BatchDownloadFile down = new BatchDownloadFile(bean); new Thread(down).start(); }

下载测试类

void main(String[] args) {          /*DownloadInfo bean = new DownloadInfo("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");         System.out.println(bean);         BatchDownloadFile down = new BatchDownloadFile(bean);         new Thread(down).start();*/                    //DownloadUtils.download("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg");          DownloadUtils.download("http://mp3.baidu.com/j?j=2 url=http%3A%2F%2Fzhangmenshiting2.baidu.com%2Fdata%2Fmusic%2F1669425%2F%25E9%2599%25B7%25E5%2585%25A5%25E7%2588%25B1%25E9%2587%258C%25E9%259D%25A2.mp3%3Fxcode%3D2ff36fb70737c816553396c56deab3f1", "aa.mp3", "c:/temp", 5);      } 
public static void main(String[] args) { /*DownloadInfo bean = new DownloadInfo("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg"); System.out.println(bean); BatchDownloadFile down = new BatchDownloadFile(bean); new Thread(down).start();*/ //DownloadUtils.download("http://i7.meishichina.com/Health/UploadFiles/201109/2011092116224363.jpg"); DownloadUtils.download("http://mp3.baidu.com/j?j=2 url=http%3A%2F%2Fzhangmenshiting2.baidu.com%2Fdata%2Fmusic%2F1669425%2F%25E9%2599%25B7%25E5%2585%25A5%25E7%2588%25B1%25E9%2587%258C%25E9%259D%25A2.mp3%3Fxcode%3D2ff36fb70737c816553396c56deab3f1", "aa.mp3", "c:/temp", 5); }多线程下载主要在第三部和第四部，其他的地方还是很好理解。源码中提供相应的注释了，便于理解。

本文转载于：http://blog.csdn.net/ibm_hoojo/article/details/6838222

Java http Post下载Excel文件 xxx.xlsx 失败解决，及传输文件类型ContentType对应关系 查询数据库生成Excel下载功能。本来很简单的功能却搞了挺久的，主要因为下载的文件打不开，且此功能已是基本功能。这里记录下来方便后面查阅。 ContentType对应的文件关系查看下面连接 https://www.runoob.com/http/mime-types.html
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