spring boot自带的json converter和fastjson对scala生成的对象，都不能很好的序列化成json。结果都会为空

解决办法：
[1] 需要序列化的类型，用kotlin定义.毕竟kotlin和scala的类定义语法基本相同
[2] 使用或者替换fastjson或者springboot的http message converter.如替换为json4s
[3] 附录：spring boot默认的converter如下：

• ByteArrayHttpMessageConverter – converts byte arrays
• StringHttpMessageConverter – converts Strings
• ResourceHttpMessageConverter – converts org.springframework.core.io.Resource for any type of octet stream
• SourceHttpMessageConverter – converts javax.xml.transform.Source
• FormHttpMessageConverter – converts form data to/from a MultiValueMap<String, String>.
• Jaxb2RootElementHttpMessageConverter – converts Java objects to/from XML (added only if JAXB2 is present on the classpath)
• MappingJackson2HttpMessageConverter – converts JSON (added only if Jackson 2 is present on the classpath)
• MappingJacksonHttpMessageConverter – converts JSON (added only if Jackson is present on the classpath)
• AtomFeedHttpMessageConverter – converts Atom feeds (added only if Rome is present on the classpath)
• RssChannelHttpMessageConverter – converts RSS feeds (added only if Rome is present on the classpath)