原理解析：

利用RandomAccessFile在本地建立一個隨機訪問檔案，檔案大小和伺服器要下載的檔案大小相同。 根據執行緒的數量（假設有三個執行緒），伺服器的檔案三等分，並把我們在本地建立的檔案同樣三等分，每個執行緒下載自己負責的部分，到相應的位置即可。

示例圖：

程式碼如下

import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class MutilDownload {
  private static String path = "http://192.168.80.85:8080/test.doc";
  private static final int threadCount = 3;

  public static void main(String[] args) {
    try {
      URL url = new URL(path);
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      conn.setRequestMethod("GET");
      conn.setConnectTimeout(5000);
      int responseCode = conn.getResponseCode();
      if (responseCode == 200) {
        int contentLength = conn.getContentLength();
        System.out.println("length" + contentLength);

        RandomAccessFile rafAccessFile = new RandomAccessFile("test.doc","rw");
        rafAccessFile.setLength(contentLength);

        int blockSize = contentLength / threadCount;
        for (int i = 0; i < threadCount; i++) {
          int startIndex = i * blockSize; //每個現成下載的開始位置
          int endIndex = (i + 1) * blockSize - 1;// 每個執行緒的結束位置
          if (i == threadCount - 1) {
            //最後一個執行緒
            endIndex = contentLength - 1;
          }

          new DownloadThread(startIndex,endIndex,i).start();
        }

      }
    } catch (Exception e) {

    }
  }

  private static class DownloadThread extends Thread {
    private int startIndex;
    private int endIndex;
    private int threadId;

    public DownloadThread(int startIndex,int endIndex,int threadId) {
      this.startIndex = startIndex;
      this.endIndex = endIndex;
      this.threadId = threadId;
    }

    @Override
    public void run() {
      try {
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5000);
        conn.setRequestProperty("Range","bytes=" + startIndex + "-" + endIndex); //固定寫法，請求部分資源
        int responseCode = conn.getResponseCode(); // 206表示請求部分資源
        if (responseCode == 206) {
          RandomAccessFile rafAccessFile = new RandomAccessFile("test.doc","rw");
          rafAccessFile.seek(startIndex);
          InputStream is = conn.getInputStream();
          int len = -1;
          byte[] buffer = new byte[1024];
          while ((len = is.read(buffer)) != -1) {
            rafAccessFile.write(buffer,len);
          }
          rafAccessFile.close();

          System.out.println("執行緒" + threadId + "下載完成");
        }
      } catch (Exception e) {

      }
    }
  }
}

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支援我們。