private int getValueAsInteger(JsonObject obj, String key, int defaultValue) {
        Object val = obj.getValue(key);
        if (val == null) {
            return defaultValue;
        } else {
            if (val instanceof Number) {
                return (int) val;
            } else if (val instanceof String) {
                return Integer.parseInt((String)val);
            }
            throw new IllegalArgumentException("Expected integer, got " + obj.getClass().getName());
        }
    }
@see io.apiman.gateway.engine.IEngineConfig#getGatewayInitializers(io.apiman.gateway.engine.IPluginRegistry)
gateway/platforms/vertx3/vertx3/src/main/java/io/apiman/gateway/platforms/vertx3/common/config/VertxEngineConfig.java