Convert Data-URL to BufferedImage

I think, a simple regex replace would be better and more conform to the RFC2397:

java.util.Base64.getDecoder().decode(b64DataString.replaceFirst("data:.+,", ""))

The RFC states that the data: and the , are the required prefixes for a data url, therefore it is wise to match for them.

The only one problem with RFC2397 string is its specification with everything before data but data: and , optional:

data:[<mediatype>][;base64],<data>

So pure Java 8 solution accounting this would be:

final int dataStartIndex = dataUrl.indexOf(",") + 1;
final String data = dataUrl.substring(dataStartIndex);
byte[] decoded = java.util.Base64.getDecoder().decode(data);

Of course dataStartIndex should be checked.

As the comments already said the image data is Base64 encoded. To retrieve the binary data you have to strip the type/encoding headers, then decode the Base64 content to binary data.

String encodingPrefix = "base64,";
int contentStartIndex = dataUrl.indexOf(encodingPrefix) + encodingPrefix.length();
byte[] imageData = Base64.decodeBase64(dataUrl.substring(contentStartIndex));

I use org.apache.commons.codec.binary.Base64 from apaches common-codec, other Base64 decoders should work as well.