gson能否转换spring data interface objections？

Question

我想在转换spring data interface objections时使用gson和HttpConverter，可是idea中报了这个错误：

org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: Attempted to serialize java.lang.Class: com.manager.projections.StaffProjection. Forgot to register a type adapter?; nested exception is java.lang.UnsupportedOperationException: Attempted to serialize java.lang.Class: com.manager.projections.StaffProjection. Forgot to register a type adapter?

请问：
1）这个错误引发的具体原因
2）能这样使用gson吗？如果不能的话，如何转换会比较合理？