Converting a request/response back to its builder about elasticsearch-java HOT 6 OPEN

  public static <T extends JsonpSerializable, B extends ObjectBuilderBase> B toObjectBuilder(
      T obj,
      Supplier<B> createBuilder,
      Predicate<String> fieldFilter) {
    B builder = createBuilder.get();
    Class<?> objClass = obj.getClass();
    Class<?> builderClass = builder.getClass();

    for (Method method : objClass.getMethods()) {
      if (fieldFilter.test(method.getName()) && method.getParameterTypes().length == 0 &&
          !Void.class.equals(method.getReturnType())) {
        // look at public, no parameter, not void return type methods. likely field accessors
        // try look for a corresponding builder method
        Method builderMethod;

        try {
          builderMethod = builderClass.getMethod(method.getName(), method.getReturnType());
        } catch (NoSuchMethodException e) {
          // the corresponding method does not exist in builder, skip
          continue;
        }

        try {
          // see if this is part of an union field
          Method kindMethod = objClass.getMethod("is" + StringUtils.capitalize(method.getName()));
          if (kindMethod.getReturnType().equals(boolean.class)) {
            if (!(boolean) kindMethod.invoke(obj)) {
              // a union kind, and the current value is not this kind
              continue;
            }
          }
        } catch (NoSuchMethodException e) {
          // not a union field
        } catch (IllegalAccessException | InvocationTargetException e) {
          throw new IllegalStateException("Unable to convert to builder.", e);
        }

        try {
          builderMethod.invoke(builder, method.invoke(obj));
        } catch (IllegalAccessException | InvocationTargetException e) {
          throw new IllegalStateException("Unable to convert to builder.", e);
        }
      }
    }

    return builder;
  }