code: private static Class getSpiClass(String type) {
          Class clazz = spiMap.get(type);
          if (clazz != null) {
              return clazz;
          }
          try {
              clazz = Class.forName("java.security." + type + "Spi");
              spiMap.put(type, clazz);
              return clazz;
          } catch (ClassNotFoundException e) {
              throw new AssertionError("Spi class not found", e);
          }
      }
docs: Return the Class object for the given engine type
  (e.g. "MessageDigest"). Works for Spis in the java.security package
  only.