base64url in java

Question

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

talks about base64Url - Decode

---

a modified Base64 for U

Answer 1

Guava now has Base64 decoding built in.

https://google.github.io/guava/releases/17.0/api/docs/com/google/common/io/BaseEncoding.html

Answer 2

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));
}

Answer 3

public static byte[] encodeUrlSafe(byte[] data) {
    byte[] encode = Base64.encode(data);
    for (int i = 0; i < encode.length; i++) {
        if (encode[i] == '+') {
            encode[i] = '-';
        } else if (encode[i] == '/') {
            encode[i] = '_';
        }
    }
    return encode;
}

public static byte[] decodeUrlSafe(byte[] data) {
    byte[] encode = Arrays.copyOf(data, data.length);
    for (int i = 0; i < encode.length; i++) {
        if (encode[i] == '-') {
            encode[i] = '+';
        } else if (encode[i] == '_') {
            encode[i] = '/';
        }
    }
    return Base64.decode(encode);
}

Answer 4

In the Android SDK, there's a dedicated flag in the Base64 class: Base64.URL_SAFE, use it like so to decode to a String:

import android.util.Base64;
byte[] byteData = Base64.decode(body, Base64.URL_SAFE);
str = new String(byteData, "UTF-8");