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基于Java實(shí)現(xiàn)多線程下載并允許斷點(diǎn)續(xù)傳

更新時(shí)間：2020年03月13日 09:09:13 作者：yuanyb

這篇文章主要介紹了基于Java實(shí)現(xiàn)多線程下載并允許斷點(diǎn)續(xù)傳,文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友可以參考下

完整代碼：https://github.com/iyuanyb/Downloader

多線程下載及斷點(diǎn)續(xù)傳的實(shí)現(xiàn)是使用 HTTP/1.1 引入的 Range 請(qǐng)求參數(shù)，可以訪問(wèn)Web資源的指定區(qū)間的內(nèi)容。雖然實(shí)現(xiàn)了多線程及斷點(diǎn)續(xù)傳，但還有很多不完善的地方。

包含四個(gè)類：

Downloader: 主類，負(fù)責(zé)分配任務(wù)給各個(gè)子線程，及檢測(cè)進(jìn)度DownloadFile: 表示要下載的哪個(gè)文件，為了能寫(xiě)輸入到文件的指定位置，使用 RandomAccessFile 類操作文件，多個(gè)線程寫(xiě)同一個(gè)文件需要保證線程安全，這里直接調(diào)用 getChannel 方法，獲取一個(gè)文件通道，F(xiàn)ileChannel是線程安全的。DownloadTask: 實(shí)際執(zhí)行下載的線程，獲取 [lowerBound, upperBound] 區(qū)間的數(shù)據(jù)，當(dāng)下載過(guò)程中出現(xiàn)異常時(shí)要通知其他線程（使用 AtomicBoolean），結(jié)束下載Logger: 實(shí)時(shí)記錄下載進(jìn)度，以便續(xù)傳時(shí)知道從哪開(kāi)始。感覺(jué)這里做的比較差，為了能實(shí)時(shí)寫(xiě)出日志及方便地使用Properties類的load/store方法格式化輸入輸出，每次都是打開(kāi)后再關(guān)閉。

演示：

隨便找一個(gè)文件下載：

強(qiáng)行結(jié)束程序并重新運(yùn)行：

日志文件：

斷點(diǎn)續(xù)傳的關(guān)鍵是記錄各個(gè)線程的下載進(jìn)度，這里細(xì)節(jié)比較多，花了很久。只需要記錄每個(gè)線程請(qǐng)求的Range區(qū)間極客，每次成功寫(xiě)數(shù)據(jù)到文件時(shí)，就更新一次下載區(qū)間。下面是下載完成后的日志內(nèi)容。

代碼:

Downloader.java

package downloader;
 
import java.io.*;
import java.net.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.concurrent.atomic.AtomicBoolean;
 
public class Downloader {
  private static final int DEFAULT_THREAD_COUNT = 4; // 默認(rèn)線程數(shù)量
  private AtomicBoolean canceled; // 取消狀態(tài)，如果有一個(gè)子線程出現(xiàn)異常，則取消整個(gè)下載任務(wù)
  private DownloadFile file; // 下載的文件對(duì)象
  private String storageLocation;
  private final int threadCount; // 線程數(shù)量
  private long fileSize; // 文件大小
  private final String url;
  private long beginTime; // 開(kāi)始時(shí)間
  private Logger logger;
 
  public Downloader(String url) {
    this(url, DEFAULT_THREAD_COUNT);
  }
 
  public Downloader(String url, int threadCount) {
    this.url = url;
    this.threadCount = threadCount;
    this.canceled = new AtomicBoolean(false);
    this.storageLocation = url.substring(url.lastIndexOf('/')+1);
    this.logger = new Logger(storageLocation + ".log", url, threadCount);
  }
 
  public void start() {
    boolean reStart = Files.exists(Path.of(storageLocation + ".log"));
    if (reStart) {
      logger = new Logger(storageLocation + ".log");
      System.out.printf("* 繼續(xù)上次下載進(jìn)度[已下載：%.2fMB]：%s\n", logger.getWroteSize() / 1014.0 / 1024, url);
    } else {
      System.out.println("* 開(kāi)始下載：" + url);
    }
    if (-1 == (this.fileSize = getFileSize()))
      return;
    System.out.printf("* 文件大?。?.2fMB\n", fileSize / 1024.0 / 1024);
 
    this.beginTime = System.currentTimeMillis();
    try {
      this.file = new DownloadFile(storageLocation, fileSize, logger);
      if (reStart) {
        file.setWroteSize(logger.getWroteSize());
      }
      // 分配線程下載
      dispatcher(reStart);
      // 循環(huán)打印進(jìn)度
      printDownloadProgress();
    } catch (IOException e) {
      System.err.println("x 創(chuàng)建文件失敗[" + e.getMessage() + "]");
    }
  }
 
  /**
   * 分配器，決定每個(gè)線程下載哪個(gè)區(qū)間的數(shù)據(jù)
   */
  private void dispatcher(boolean reStart) {
    long blockSize = fileSize / threadCount; // 每個(gè)線程要下載的數(shù)據(jù)量
    long lowerBound = 0, upperBound = 0;
    long[][] bounds = null;
    int threadID = 0;
    if (reStart) {
      bounds = logger.getBounds();
    }
    for (int i = 0; i < threadCount; i++) {
      if (reStart) {
        threadID = (int)(bounds[i][0]);
        lowerBound = bounds[i][1];
        upperBound = bounds[i][2];
      } else {
        threadID = i;
        lowerBound = i * blockSize;
        // fileSize-1 !!!!! fu.ck，找了一下午的錯(cuò)
        upperBound = (i == threadCount - 1) ? fileSize-1 : lowerBound + blockSize;
      }
      new DownloadTask(url, lowerBound, upperBound, file, canceled, threadID).start();
    }
  }
 
  /**
   * 循環(huán)打印進(jìn)度，直到下載完畢，或任務(wù)被取消
   */
  private void printDownloadProgress() {
    long downloadedSize = file.getWroteSize();
    int i = 0;
    long lastSize = 0; // 三秒前的下載量
    while (!canceled.get() && downloadedSize < fileSize) {
      if (i++ % 4 == 3) { // 每3秒打印一次
        System.out.printf("下載進(jìn)度：%.2f%%, 已下載：%.2fMB，當(dāng)前速度：%.2fMB/s\n",
            downloadedSize / (double)fileSize * 100 ,
            downloadedSize / 1024.0 / 1024,
            (downloadedSize - lastSize) / 1024.0 / 1024 / 3);
        lastSize = downloadedSize;
        i = 0;
      }
      try {
        Thread.sleep(1000);
      } catch (InterruptedException ignore) {}
      downloadedSize = file.getWroteSize();
    }
    file.close();
    if (canceled.get()) {
      try {
        Files.delete(Path.of(storageLocation));
      } catch (IOException ignore) {
      }
      System.err.println("x 下載失敗，任務(wù)已取消");
    } else {
      System.out.println("* 下載成功，本次用時(shí)"+ (System.currentTimeMillis() - beginTime) / 1000 +"秒");
    }
  }
 
  /**
   * @return 要下載的文件的尺寸
   */
  private long getFileSize() {
    if (fileSize != 0) {
      return fileSize;
    }
    HttpURLConnection conn = null;
    try {
      conn = (HttpURLConnection)new URL(url).openConnection();
      conn.setConnectTimeout(3000);
      conn.setRequestMethod("HEAD");
      conn.connect();
      System.out.println("* 連接服務(wù)器成功");
    } catch (MalformedURLException e) {
      throw new RuntimeException("URL錯(cuò)誤");
    } catch (IOException e) {
      System.err.println("x 連接服務(wù)器失敗["+ e.getMessage() +"]");
      return -1;
    }
    return conn.getContentLengthLong();
  }
 
  public static void main(String[] args) throws IOException {
    new Downloader("http://js.xiazaicc.com//down2/ucliulanqi_downcc.zip").start();
  }
}

DownloadTask.java

package downloader;
 
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.util.concurrent.atomic.AtomicBoolean;
 
class DownloadTask extends Thread {
  private final String url;
  private long lowerBound; // 下載的文件區(qū)間
  private long upperBound;
  private AtomicBoolean canceled;
  private DownloadFile downloadFile;
  private int threadId;
 
  DownloadTask(String url, long lowerBound, long upperBound, DownloadFile downloadFile,
            AtomicBoolean canceled, int threadID) {
    this.url = url;
    this.lowerBound = lowerBound;
    this.upperBound = upperBound;
    this.canceled = canceled;
    this.downloadFile = downloadFile;
    this.threadId = threadID;
  }
 
  @Override
  public void run() {
    ReadableByteChannel input = null;
    try {
      ByteBuffer buffer = ByteBuffer.allocate(1024 * 1024 * 2); // 2MB
      input = connect();
      System.out.println("* [線程" + threadId + "]連接成功，開(kāi)始下載...");
 
      int len;
      while (!canceled.get() && lowerBound <= upperBound) {
        buffer.clear();
        len = input.read(buffer);
        downloadFile.write(lowerBound, buffer, threadId, upperBound);
        lowerBound += len;
      }
      if (!canceled.get()) {
        System.out.println("* [線程" + threadId + "]下載完成" + ": " + lowerBound + "-" + upperBound);
      }
    } catch (IOException e) {
      canceled.set(true);
      System.err.println("x [線程" + threadId + "]遇到錯(cuò)誤[" + e.getMessage() + "]，結(jié)束下載");
    } finally {
      if (input != null) {
        try {
          input.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
  }
 
  /**
   * 連接WEB服務(wù)器，并返回一個(gè)數(shù)據(jù)通道
   * @return 返回通道
   * @throws IOException 網(wǎng)絡(luò)連接錯(cuò)誤
   */
  private ReadableByteChannel connect() throws IOException {
    HttpURLConnection conn = (HttpURLConnection)new URL(url).openConnection();
    conn.setConnectTimeout(3000);
    conn.setRequestMethod("GET");
    conn.setRequestProperty("Range", "bytes=" + lowerBound + "-" + upperBound);
//    System.out.println("thread_"+ threadId +": " + lowerBound + "-" + upperBound);
    conn.connect();
 
    int statusCode = conn.getResponseCode();
    if (HttpURLConnection.HTTP_PARTIAL != statusCode) {
      conn.disconnect();
      throw new IOException("狀態(tài)碼錯(cuò)誤：" + statusCode);
    }
 
    return Channels.newChannel(conn.getInputStream());
  }
}

DownloadFile.java

package downloader;
 
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.util.concurrent.atomic.AtomicLong;
 
class DownloadFile {
  private final RandomAccessFile file;
  private final FileChannel channel; // 線程安全類
  private AtomicLong wroteSize; // 已寫(xiě)入的長(zhǎng)度
  private Logger logger;
 
  DownloadFile(String fileName, long fileSize, Logger logger) throws IOException {
    this.wroteSize = new AtomicLong(0);
    this.logger = logger;
    this.file = new RandomAccessFile(fileName, "rw");
    file.setLength(fileSize);
    channel = file.getChannel();
  }
 
  /**
   * 寫(xiě)數(shù)據(jù)
   * @param offset 寫(xiě)偏移量
   * @param buffer 數(shù)據(jù)
   * @throws IOException 寫(xiě)數(shù)據(jù)出現(xiàn)異常
   */
  void write(long offset, ByteBuffer buffer, int threadID, long upperBound) throws IOException {
    buffer.flip();
    int length = buffer.limit();
    while (buffer.hasRemaining()) {
      channel.write(buffer, offset);
    }
    wroteSize.addAndGet(length);
    logger.updateLog(threadID, length, offset + length, upperBound); // 更新日志
  }
 
  /**
   * @return 已經(jīng)下載的數(shù)據(jù)量，為了知道何時(shí)結(jié)束整個(gè)任務(wù)，以及統(tǒng)計(jì)信息
   */
  long getWroteSize() {
    return wroteSize.get();
  }
 
  // 繼續(xù)下載時(shí)調(diào)用
  void setWroteSize(long wroteSize) {
    this.wroteSize.set(wroteSize);
  }
 
  void close() {
    try {
      file.close();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

Logger.java

package downloader;
 
import java.io.*;
import java.util.Properties;
 
class Logger {
  private String logFileName; // 下載的文件的名字
  private Properties log;
 
   /**
   * 重新開(kāi)始下載時(shí)，使用該構(gòu)造函數(shù)
   * @param logFileName
   */
  Logger(String logFileName) {
    this.logFileName = logFileName;
    log = new Properties();
    FileInputStream fin = null;
    try {
      log.load(new FileInputStream(logFileName));
    } catch (IOException ignore) {
    } finally {
      try {
        fin.close();
      } catch (Exception ignore) {}
    }
  }
 
  Logger(String logFileName, String url, int threadCount) {
    this.logFileName = logFileName;
    this.log = new Properties();
    log.put("url", url);
    log.put("wroteSize", "0");
    log.put("threadCount", String.valueOf(threadCount));
    for (int i = 0; i < threadCount; i++) {
      log.put("thread_" + i, "0-0");
    }
  }
 
 
  synchronized void updateLog(int threadID, long length, long lowerBound, long upperBound) {
    log.put("thread_"+threadID, lowerBound + "-" + upperBound);
    log.put("wroteSize", String.valueOf(length + Long.parseLong(log.getProperty("wroteSize"))));
 
    FileOutputStream file = null;
    try {
      file = new FileOutputStream(logFileName); // 每次寫(xiě)時(shí)都清空文件
      log.store(file, null);
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      if (file != null) {
        try {
          file.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
  }
 
  /**
   * 獲取區(qū)間信息
   *   ret[i][0] = threadID, ret[i][1] = lowerBoundID, ret[i][2] = upperBoundID
   * @return
   */
  long[][] getBounds() {
    long[][] bounds = new long[Integer.parseInt(log.get("threadCount").toString())][3];
    int[] index = {0};
    log.forEach((k, v) -> {
      String key = k.toString();
      if (key.startsWith("thread_")) {
        String[] interval = v.toString().split("-");
        bounds[index[0]][0] = Long.parseLong(key.substring(key.indexOf("_") + 1));
        bounds[index[0]][1] = Long.parseLong(interval[0]);
        bounds[index[0]++][2] = Long.parseLong(interval[1]);
      }
    });
    return bounds;
  }
  long getWroteSize() {
    return Long.parseLong(log.getProperty("wroteSize"));
  }
}

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