使用JSON格式请求时，添加@RequestBody注解映射实体类

.16:59:02.449 [http-nio-8081-exec-2] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.InvalidDataAccessApiUsageException: Target object must not be null; nested exception is java.lang.IllegalArgumentException: Target object must not be null] with root cause java.lang.IllegalArgumentException: Target object must not be null	at org.springframework.util.Assert.notNull(Assert.java:193)	at org.springframework.beans.AbstractNestablePropertyAccessor.setWrappedInstance(AbstractNestablePropertyAccessor.java:195)	at org.springframework.beans.BeanWrapperImpl.setWrappedInstance(BeanWrapperImpl.java:153)	at org.springframework.beans.AbstractNestablePropertyAccessor.setWrappedInstance(AbstractNestablePropertyAccessor.java:183)	at org.springframework.beans.AbstractNestablePropertyAccessor.
    
     (AbstractNestablePropertyAccessor.java:122)	at org.springframework.beans.BeanWrapperImpl.
     
      (BeanWrapperImpl.java:103)