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Java多线程下载文件实例详解

时间:2020-09-06 15:07     来源/作者:欧阳鹏

本文实例为大家分享了Java多线程下载文件的具体代码,供大家参考,具体内容如下

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import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
 
public class MulThreadDownload {
  public static void main(String[] args) throws Exception {
    String path = "http://192.168.1.100:8080/Hello/Big.exe";
    new MulThreadDownload().download(path, 3);
  }
 
  /**
   * 下载文件
   *
   * @param path
   *      网络文件路径
   * @param threadSize
   *      线程数
   * @throws Exception
   */
  private void download(String path, int threadSize) throws Exception {
    URL url = new URL(path);
    HttpURLConnection connection = (HttpURLConnection) url.openConnection();
    connection.setRequestMethod("GET");
    connection.setConnectTimeout(5000);
    if (connection.getResponseCode() == 200) {
      int length = connection.getContentLength();// 获取网络文件长度
      File file = new File(getFileName(path));
      // 在本地生成一个长度与网络文件相同的文件
      RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
      accessFile.setLength(length);
      accessFile.close();
 
      // 计算每条线程负责下载的数据量
      int block = length % threadSize == 0 ? length / threadSize : length
          / threadSize + 1;
      for (int threadId = 0; threadId < threadSize; threadId++) {
        new DownloadThread(threadId, block, url, file).start();
      }
    } else {
      System.out.println("download fail");
    }
  }
 
  private class DownloadThread extends Thread {
 
    private int threadId;
    private int block;
    private URL url;
    private File file;
 
    public DownloadThread(int threadId, int block, URL url, File file) {
      this.threadId = threadId;
      this.block = block;
      this.url = url;
      this.file = file;
    }
 
    @Override
    public void run() {
      int start = threadId * block; // 计算该线程从网络文件什么位置开始下载
      int end = (threadId + 1) * block - 1; // 计算下载到网络文件什么位置结束
      try {
        RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
        accessFile.seek(start); //从start开始
 
        HttpURLConnection connection = (HttpURLConnection) url
            .openConnection();
        connection.setRequestMethod("GET");
        connection.setConnectTimeout(5000);
        //设置获取资源数据的范围,从start到end
        connection.setRequestProperty("Range", "bytes=" + start + "-"
            + end);
        //注意多线程下载状态码是 206 不是200
        if (connection.getResponseCode() == 206) {
          InputStream inputStream = connection.getInputStream();
          byte[] buffer = new byte[1024];
          int len = 0;
          while ((len = inputStream.read(buffer)) != -1) {
            accessFile.write(buffer, 0, len);
          }
          accessFile.close();
          inputStream.close();
        }
        System.out.println("第" + (threadId + 1) + "条线程已经下载完成");
      } catch (Exception e) {
        e.printStackTrace();
      }
    }
  }
 
  /**
   * 获取文件名称
   *
   * @param path
   *      网络文件路径
   * @return
   */
  private String getFileName(String path) {
    return path.substring(path.lastIndexOf("/") + 1);
  }
}

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。

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