Decode base64Url in Java

https://web.archive.org/web/20110422225659/https://en.wikipedia.org/wiki/Base64#URL_applications

talks about base64Url – Decode

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a modified Base64 for URL variant exists, where no padding ‘=’ will be used, and the ‘+’ and ‘/’ characters of standard Base64 are respectively replaced by ‘-‘ and ‘_’

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I created the following function:

public static String base64UrlDecode(String input) {
    String result = null;
    BASE64Decoder decoder = new BASE64Decoder();
    try {
        result = decoder.decodeBuffer(input.replace('-','+').replace('/','_')).toString();
    }
    catch (IOException e) {
        System.out.println(e.getMessage());
    }
    return result;
}

it returns a very small set of characters that don’t even resemble to the expected results. any ideas?

Answer

With the usage of Base64 from Apache Commons, who can be configured to URL safe, I created the following function:

import org.apache.commons.codec.binary.Base64;

public static String base64UrlDecode(String input) {
    String result = null;
    Base64 decoder = new Base64(true);
    byte[] decodedBytes = decoder.decode(input);
    result = new String(decodedBytes);
    return result;
}

The constructor Base64(true) makes the decoding URL-safe.