https://web.archive.org/web/20110422225659/https://en.wikipedia.org/wiki/Base64#URL_applications
talks about base64Url - Decode
a modified Base64 for U
Base64 encoding is part of the JDK since Java 8. URL safe encoding is also supported with java.util.Base64.getUrlEncoder(), and the "=" padding can be skipped by additionally using the java.util.Base64.Encoder.withoutPadding() method:
import java.nio.charset.StandardCharsets;
import java.util.Base64;
public String encode(String raw) {
return Base64.getUrlEncoder()
.withoutPadding()
.encodeToString(raw.getBytes(StandardCharsets.UTF_8));
}