Unescape MQL keys (wiki.freebase.com/wiki/MQL_key_escaping) - adapted from https://github.com/apache/commons-lang/blob/trunk/src/main/java/org/apache/commons/lang3/text/translate/UnicodeUnescaper.java

MqlKey.java

public class MqlKey {
	public static CharSequence unescape(final CharSequence input) {
		final StringBuilder output = new StringBuilder();
		for (int index = 0; index < input.length(); ++index) {
			final char current = input.charAt(index);
			if ('$' != current) {
				output.append(current);
				continue;
			}

			if (index + 5 > input.length()) {
				throw new IllegalArgumentException(
						"Unicode char with less than 4 hex digits?!");
			}

			final CharSequence hex = input.subSequence(index + 1, index + 5);
			try {
				final char value = (char) Integer.parseInt(hex.toString(), 16);
				output.append(value);
			} catch (final NumberFormatException ex) {
				throw new IllegalArgumentException(
						"Sequence cannot be parsed as unicode:" + hex, ex);
			}

			index += 4; // Skip past the hex value?
		}

		return output.toString();
	}
}