private FastJsonContainer getOrCreateContainer(Object body) {
        return (body instanceof FastJsonContainer ? (FastJsonContainer) body : new FastJsonContainer(body));

    }
A convenient base class for {@code ResponseBodyAdvice} implementations
that customize the response before JSON serialization with {@link FastJsonHttpMessageConverter4}'s concrete
subclasses.
<p>

@author yanquanyu
@author liuming
src/main/java/com/alibaba/fastjson/support/spring/FastJsonViewResponseBodyAdvice.java