JAVA线程实现下载_JAVA代码实现多线程下载

好的，我可以为您提供一段Java代码实现多线程下载：

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

public class MultiThreadDownload extends Thread {
    private String url; // 文件下载地址
    private String filePath; // 保存路径
    private int threadNum; // 线程数量

    public MultiThreadDownload(String url, String filePath, int threadNum) {
        this.url = url;
        this.filePath = filePath;
        this.threadNum = threadNum;
    }

    @Override
    public void run() {
        try {
            URL downloadUrl = new URL(url);
            HttpURLConnection httpURLConnection = (HttpURLConnection) downloadUrl.openConnection();
            httpURLConnection.setRequestMethod("GET");
            httpURLConnection.setConnectTimeout(5000);

            int fileLength = httpURLConnection.getContentLength();
            int blockSize = fileLength % threadNum == 0 ? fileLength / threadNum : fileLength / threadNum + 1;

            RandomAccessFile randomAccessFile = new RandomAccessFile(filePath, "rw");
            randomAccessFile.setLength(fileLength);
            randomAccessFile.close();

            for (int i = 0; i < threadNum; i++) {
                int startIndex = i * blockSize;
                int endIndex = (i + 1) * blockSize - 1;
                if (endIndex > fileLength) endIndex = fileLength;

                new DownloadThread(url, filePath, startIndex, endIndex).start();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private class DownloadThread extends Thread {
        private String url;
        private String filePath;
        private int startIndex;
        private int endIndex;

        public DownloadThread(String url, String filePath, int startIndex, int endIndex) {
            this.url = url;
            this.filePath = filePath;
            this.startIndex = startIndex;
            this.endIndex = endIndex;
        }

        @Override
        public void run() {
            try {
                RandomAccessFile randomAccessFile = new RandomAccessFile(filePath, "rw");
                randomAccessFile.seek(startIndex);

                URL downloadUrl = new URL(url);
                HttpURLConnection httpURLConnection = (HttpURLConnection) downloadUrl.openConnection();
                httpURLConnection.setRequestMethod("GET");
                httpURLConnection.setConnectTimeout(5000);
                httpURLConnection.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);

                InputStream inputStream = httpURLConnection.getInputStream();
                byte[] buffer = new byte[1024];
                int length = -1;
                while ((length = inputStream.read(buffer)) != -1) {
                    randomAccessFile.write(buffer, 0, length);
                }

                inputStream.close();
                randomAccessFile.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

这段代码利用多线程实现文件下载，具体实现过程为：首先获取文件长度，然后根据线程数量计算每个线程需要下载的文件块大小，接着创建多个下载线程，每个下载线程负责下载自己对应的文件块。在下载时，通过设置请求头中的 `Range` 参数实现分块下载，最终将所有分块拼接起来得到完整的文件。