Java多连接下载文件

Question

我想在下面的代码中添加多个连接以便能够更快地下载文件。有人可以帮助我吗？提前致谢。

public void run() {
    RandomAccessFile file = null;
    InputStream stream = null;

    try {
        // Open connection to URL.
        HttpURLConnection connection =
                (HttpURLConnection) url.openConnection();

        // Specify what portion of file to download.
        connection.setRequestProperty("Range",
                "bytes=" + downloaded + "-");

        // Connect to server.
        connection.connect();

        // Make sure response code is in the 200 range.
        if (connection.getResponseCode() / 100 != 2) {
            error();
        }

        // Check for valid content length.
        int contentLength = connection.getContentLength();
        if (contentLength < 1) {
            error();
        }

        /* Set the size for this download if it
        hasn't been already set. */
        if (size == -1) {
            size = contentLength;
            stateChanged();
        }

        // Open file and seek to the end of it.
        file = new RandomAccessFile("C:\\"+getFileName(url), "rw");
        file.seek(downloaded);

        stream = connection.getInputStream();
        while (status == DOWNLOADING) {
            /* Size buffer according to how much of the
            file is left to download. */
            byte buffer[];
            if (size - downloaded > MAX_BUFFER_SIZE) {
                buffer = new byte[MAX_BUFFER_SIZE];
            } else {
                buffer = new byte[size - downloaded];
            }

            // Read from server into buffer.
            int read = stream.read(buffer);
            if (read == -1) {
                break;
            }

            // Write buffer to file.
            file.write(buffer, 0, read);
            downloaded += read;
            stateChanged();
        }

        /* Change status to complete if this point was
        reached because downloading has finished. */
        if (status == DOWNLOADING) {
            status = COMPLETE;
            stateChanged();
        }
    } catch (Exception e) {
        error();
    } finally {
        // Close file.
        if (file != null) {
            try {
                file.close();
            } catch (Exception e) {
            }
        }

        // Close connection to server.
        if (stream != null) {
            try {
                stream.close();
            } catch (Exception e) {
            }
        }
    }
}

Answer 1

您可以使用线程。

将下载和更新 RandomAccessFile 的代码放入 Thread/Runnable 中，并启动它的多个实例。

使用全局计数器（同步访问）来跟踪有多少线程完成下载，并让主线程等待，直到所有线程都增加计数器后再关闭文件。

确保同步对 RandomAccessFile 的所有访问，以便线程 A 在线程 B 写入文件的另一部分时无法调用 seek(somePosition)。

Answer 2

确保你描述了你的想法。多个线程的开销以及它们之间的协调可能会使您的代码变慢。
除非您确定这是瓶颈，否则不要这样做，代码复杂性会增加并且调试这很重要。