code: public static String appendPath (String source, String affix)
      {
          if (source.endsWith("/")) {
              if (affix.startsWith("/")) {
                  return source + affix.substring(1);
              } else {
                  return source + affix;
              }
          } else if (affix.startsWith("/")) {
              return source + affix;
          } else {
              return source + "/" + affix;
          }
      }
docs: Appends the supplied affix to the specified source path, ensuring
  that exactly one path separator (<code>/</code> as we are dealing
  with URLs here not platform specific file-system paths) is used
  between the two. <em>Note:</em> this means that the affix will be
  made into a relative path regardless of whether or not it starts
  with a <code>/</code>.