Use this method to join arrays:
//for List of strings
public static String join(List<String> listStrings, String separator) {
  String[] sl = (String[]) listStrings.toArray(new String[]{});
  return join(sl, separator);
}
/**
 * Joins an array of string with the given separator
 * @param strings array of string
 * @param separator string to join with
 * @return a single joined string from array 
 */
public static String join(String[] strings, String separator) {
    StringBuffer sb = new StringBuffer();
    for (int i=0; i < strings.length; i++) {
        if (i != 0) sb.append(separator);
        sb.append(strings[i]);
    }
    return sb.toString();
}