springboot @ResponseBody 返回对象报错解决

错误日志如下：
[org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver] [DefaultHandlerExceptionResolver.java:447] Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: No converter found for return value of type: class xxxx

原因：
返回的对象没写get/set方法