Parse file name from URL before downloading the file

Question

I'm downloading an ePub file from a URL.

Now I want to implement a mechanism by which if user tries to re-download the same file, he should get warning/error message and that file should not be downloaded again.

To implement this, I need to check the name of the file present in my library with the name of the file user is trying to download.

But I just have this download link, and not the file name.

How to get the name of the file before download in order to compare it with the existing file?

Answer 1

In android you can use the guessFileName() method:

URLUtil.guessFileName(url, null, null) 

Alternatively, a simplistic solution in Java could be:

String fileName = url.substring(url.lastIndexOf('/') + 1); 

(Assuming your url is in the format: http://xxxxxxxxxxxxx/filename.ext)

UPDATE March 23, 2018

This question is getting lots of hits and someone commented my 'simple' solution does not work with certain urls so I felt the need to improve the answer.

In case you want to handle more complex url pattern, I provided a sample solution below. It gets pretty complex quite quickly and I'm pretty sure there are some odd cases my solution still can't handle but nevertheless here it goes:

public static String getFileNameFromURL(String url) {     if (url == null) {         return "";     }     try {         URL resource = new URL(url);         String host = resource.getHost();         if (host.length() > 0 && url.endsWith(host)) {             // handle ...example.com             return "";         }     }     catch(MalformedURLException e) {         return "";       }      int startIndex = url.lastIndexOf('/') + 1;     int length = url.length();      // find end index for ?     int lastQMPos = url.lastIndexOf('?');     if (lastQMPos == -1) {         lastQMPos = length;      }      // find end index for #     int lastHashPos = url.lastIndexOf('#');     if (lastHashPos == -1) {         lastHashPos = length;        }      // calculate the end index     int endIndex = Math.min(lastQMPos, lastHashPos);     return url.substring(startIndex, endIndex); } 

This method can handle these type of input:

Input: "null" Output: "" Input: "" Output: "" Input: "file:///home/user/test.html" Output: "test.html" Input: "file:///home/user/test.html?id=902" Output: "test.html" Input: "file:///home/user/test.html#footer" Output: "test.html" Input: "http://example.com" Output: "" Input: "http://www.example.com" Output: "" Input: "http://www.example.txt" Output: "" Input: "http://example.com/" Output: "" Input: "http://example.com/a/b/c/test.html" Output: "test.html" Input: "http://example.com/a/b/c/test.html?param=value" Output: "test.html" Input: "http://example.com/a/b/c/test.html#anchor" Output: "test.html" Input: "http://example.com/a/b/c/test.html#anchor?param=value" Output: "test.html" 

You can find the whole source code here: https://ideone.com/uFWxTL