Простой фрагмент:
public static String camelCase(String in) {
if (in == null || in.length() < 1) { return ""; } //validate in
String out = "";
for (String part : in.toLowerCase().split("_")) {
if (part.length() < 1) { //validate length
continue;
}
out += part.substring(0, 1).toUpperCase();
if (part.length() > 1) { //validate length
out += part.substring(1);
}
}
return out;
}