在Java中下载文件时如何获取文件名？

Question

I have FileDownloader class that downloads the file from google drive and than these files can be used by other classes. I need also to extract filename somehow. The problem is that this solution below works good for direct links, but it doesn't work when links are shorten with bit.ly for example... Could you please advise how I can change the code to get the right file name?

public class FileDownloader {

private static final int BUFFER_SIZE = 4096;


public static void downloadFile(String fileURL, String saveDir)
        throws IOException {
    URL url = new URL(fileURL);
    HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
    int responseCode = httpConn.getResponseCode();

    // checking HTTP response code first
    if (responseCode == HttpURLConnection.HTTP_OK) {
        String fileName = "";
        String disposition = httpConn.getHeaderField("Content-Disposition");
        String contentType = httpConn.getContentType();
        int contentLength = httpConn.getContentLength();

        if (disposition != null) {
            // extracts file name from header field
            int index = disposition.indexOf("filename*=UTF-8''");

            if (index > 0) {
                fileName = disposition.substring(index + 17,
                        disposition.length());
            }
        } else {
            // extracts file name from URL
            fileName = fileURL.substring(fileURL.lastIndexOf("/") + 1,
                    fileURL.length());
        }

        System.out.println("Content-Type = " + contentType);
        System.out.println("Content-Disposition = " + disposition);
        System.out.println("Content-Length = " + contentLength);
        System.out.println("fileName = " + fileName);

        // opens input stream from the HTTP connection
        InputStream inputStream = httpConn.getInputStream();
        String saveFilePath = saveDir + File.separator + fileName;

        // opens an output stream to save into file
        FileOutputStream outputStream = new FileOutputStream(saveFilePath);

        int bytesRead = -1;
        byte[] buffer = new byte[BUFFER_SIZE];
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }

        outputStream.close();
        inputStream.close();

        System.out.println("File downloaded");
    } else {
        System.out.println("No file to download. Server replied HTTP code: " +  responseCode);
    }
    httpConn.disconnect();
}

Answer 1

Alternate Code to get File details from any HTTP URL using Java API:

URL url = new URL(" http://www.example.com/somepath/filename.extension ");

    System.out.println(FilenameUtils.getBaseName(url.getPath())); 

// filename

    System.out.println(FilenameUtils.getName(url.getPath())); 

// filename.extension