jodd-core/src/main/java/jodd/util/StringUtil.java
public static String prefix(String string, final String prefix) {
		if (!string.startsWith(prefix)) {
			string = prefix + string;
		}
		return string;
	}
public static String prefix(String string, final String prefix) {
		if (!string.startsWith(prefix)) {
			string = prefix + string;
		}
		return string;
	}
Inserts prefix if doesn't exist.