查看MappingJackson2HttpMessageConverter源码注释：
Implementation of {@link org.springframework.http.converter.HttpMessageConverter} that can read and
* write JSON using <a href="http://wiki.fasterxml.com/JacksonHome">Jackson 2.x's</a> {@link ObjectMapper}.
*
* <p>This converter can be used to bind to typed beans, or untyped {@code HashMap} instances.
*
* <p>By default, this converter supports {@code application/json} and {@code application/*+json}
* with {@code UTF-8} character set. This can be overridden by setting the
* {@link #setSupportedMediaTypes supportedMediaTypes} property.
*
* <p>The default constructor uses the default configuration provided by {@link Jackson2ObjectMapperBuilder}.
*
* <p>Compatible with Jackson 2.9 and higher, as of Spring 5.0.
最后一句为：兼容Jackson 2.9或更高版本，从Spring 5.0开始。