使用Java Apache Commons下载文件？

使用Java Apache Commons下载文件？

如果您正在寻找一种在下载之前获取字节总数的方法，则可以从

Content-Length

http响应的标头中获取此值。

如果只需要下载后的最终字节数，则最简单的方法就是检查刚刚写入的文件大小。

但是，如果要显示当前已下载多少字节的进度，则可能需要扩展apache

CountingOutputStream

来包装，

FileOutputStream

以便每次

write

调用方法时，它都会计算通过的字节数并更新进度条。

更新资料

这是的简单实现

DownloadCountingOutputStream

。我不确定您是否熟悉使用

ActionListener

它，但是它对于实现GUI是有用的。

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));        }    }}

这是用法示例：

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);        }    }}