Decode Base64 data in Java

Question

I have an image that is Base64 encoded. What is the best way to decode that in Java? Hopefully using only the libraries included with Sun Java 6.

Answer 1

In a code compiled with Java 7 but potentially running in a higher java version, it seems useful to detect presence of java.util.Base64 class and use the approach best for given JVM mentioned in other questions here.

I used this code:

private static final Method JAVA_UTIL_BASE64_GETENCODER;

static {
    Method getEncoderMethod;
    try {
        final Class base64Class = Class.forName("java.util.Base64");
        getEncoderMethod = base64Class.getMethod("getEncoder");
    } catch (ClassNotFoundException | NoSuchMethodException e) {
        getEncoderMethod = null;
    }
    JAVA_UTIL_BASE64_GETENCODER = getEncoderMethod;
}

static String base64EncodeToString(String s) {
    final byte[] bytes = s.getBytes(StandardCharsets.ISO_8859_1);
    if (JAVA_UTIL_BASE64_GETENCODER == null) {
        // Java 7 and older // TODO: remove this branch after switching to Java 8
        return DatatypeConverter.printBase64Binary(bytes);
    } else {
        // Java 8 and newer
        try {
            final Object encoder = JAVA_UTIL_BASE64_GETENCODER.invoke(null);
            final Class encoderClass = encoder.getClass();
            final Method encodeMethod = encoderClass.getMethod("encode", byte[].class);
            final byte[] encodedBytes = (byte[]) encodeMethod.invoke(encoder, bytes);
            return new String(encodedBytes);
        } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
            throw new IllegalStateException(e);
        }
    }
}