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。有人能帮助我吗？提前谢谢。

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

你可以使用线程。

将用于下载和更新RandomAccessFile的代码放在Thread / Runnable中并启动它的多个实例。

使用全局计数器（同步访问）来跟踪完成下载的线程数，并使主线程等到所有线程都在关闭文件之前增加计数器。

确保同步对RandomAccessFile的所有访问，以便线程A在写入文件的另一部分时不能调用seek(somePosition)。

Answer 2

确保描述您的想法。多线程的开销和它们之间的协调可能会使代码变慢。不要这样做，除非你确定这是一个瓶颈，代码复杂性会增加，调试这是非常重要的。

Java多个连接下载文件

2 个答案: