使用java apache commons下载文件？ [英] Download file using java apache commons?

问题描述

如何使用库下载文件并打印保存的字节？我尝试使用

How can I use the library to download a file and print out bytes saved? I tried using

import static org.apache.commons.io.FileUtils.copyURLToFile;
public static void Download() {

        URL dl = null;
        File fl = null;
        try {
            fl = new File(System.getProperty("user.home").replace("\\", "/") + "/Desktop/Screenshots.zip");
            dl = new URL("http://ds-forums.com/kyle-tests/uploads/Screenshots.zip");
            copyURLToFile(dl, fl);
        } catch (Exception e) {
            System.out.println(e);
        }
    }

但我无法显示字节或进度条。我应该使用哪种方法？

but I cannot display bytes or a progress bar. Which method should I use?

public class download {
    public static void Download() {
        URL dl = null;
        File fl = null;
        String x = null;
        try {
            fl = new File(System.getProperty("user.home").replace("\\", "/") + "/Desktop/Screenshots.zip");
            dl = new URL("http://ds-forums.com/kyle-tests/uploads/Screenshots.zip");
            OutputStream os = new FileOutputStream(fl);
            InputStream is = dl.openStream();
            CountingOutputStream count = new CountingOutputStream(os);
            dl.openConnection().getHeaderField("Content-Length");
            IOUtils.copy(is, os);//begin transfer

            os.close();//close streams
            is.close();//^
        } catch (Exception e) {
            System.out.println(e);
        }
    }

推荐答案

如果您正在寻找一种在下载前获取总字节数的方法，您可以从http响应中的 Content-Length 标题中获取此值。

If you are looking for a way to get the total number of bytes before downloading, you can obtain this value from the Content-Length header in http response.

如果您只想要下载后的最终字节数，最简单的方法是检查您刚写入的文件大小。

If you just want the final number of bytes after the download, it is easiest to check the file size you just write to.

但是，如果要显示已下载的字节数的当前进度，可能需要扩展apache CountingOutputStream 以包装 FileOutputStream 以便每次调用 write 方法时，它会计算通过的字节数并更新进度条。

However if you want to display the current progress of how many bytes have been downloaded, you might want to extend apache CountingOutputStream to wrap the FileOutputStream so that everytime the write methods are called it counts the number of bytes passing through and update the progress bar.

更新

以下是 DownloadCountingOutputStream 的简单实现。我不确定你是否熟悉使用 ActionListener ，但它是一个用于实现GUI的有用类。

Here is a simple implementation of DownloadCountingOutputStream. I am not sure if you are familiar with using ActionListener or not but it is a useful class for implementing GUI.

public class DownloadCountingOutputStream extends CountingOutputStream {

    private ActionListener listener = null;

    public DownloadCountingOutputStream(OutputStream out) {
        super(out);
    }

    public void setListener(ActionListener listener) {
        this.listener = listener;
    }

    @Override
    protected void afterWrite(int n) throws IOException {
        super.afterWrite(n);
        if (listener != null) {
            listener.actionPerformed(new ActionEvent(this, 0, null));
        }
    }

}

这是使用示例：

public class Downloader {

    private static class ProgressListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent e) {
            // e.getSource() gives you the object of DownloadCountingOutputStream
            // because you set it in the overriden method, afterWrite().
            System.out.println("Downloaded bytes : " + ((DownloadCountingOutputStream) e.getSource()).getByteCount());
        }
    }

    public static void main(String[] args) {
        URL dl = null;
        File fl = null;
        String x = null;
        OutputStream os = null;
        InputStream is = null;
        ProgressListener progressListener = new ProgressListener();
        try {
            fl = new File(System.getProperty("user.home").replace("\\", "/") + "/Desktop/Screenshots.zip");
            dl = new URL("http://ds-forums.com/kyle-tests/uploads/Screenshots.zip");
            os = new FileOutputStream(fl);
            is = dl.openStream();

            DownloadCountingOutputStream dcount = new DownloadCountingOutputStream(os);
            dcount.setListener(progressListener);

            // this line give you the total length of source stream as a String.
            // you may want to convert to integer and store this value to
            // calculate percentage of the progression.
            dl.openConnection().getHeaderField("Content-Length");

            // begin transfer by writing to dcount, not os.
            IOUtils.copy(is, dcount);

        } catch (Exception e) {
            System.out.println(e);
        } finally {
            IOUtils.closeQuietly(os);
            IOUtils.closeQuietly(is);
        }
    }
}

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