[org.springframework.web.bind.MissingServletRequestParameterException: Required String parameter 'xxx ' is not present]

1、Spring Boot项目，发起Post请求，解决Required String parameter xxx is not present类型异常。

2021-03-29 08:43:52 - [http-nio-8082-exec-1] - WARN  - o.s.w.s.m.support.DefaultHandlerExceptionResolver - Resolved [org.springframework.web.bind.MissingServletRequestParameterException: Required String parameter 'xxx ' is not present]
2021-03-29 08:43:52 - [http-nio-8082-exec-1] - DEBUG - org.springframework.web.servlet.DispatcherServlet - Completed 400 BAD_REQUEST
2021-03-29 08:43:52 - [http-nio-8082-exec-1] - DEBUG - org.springframework.web.servlet.DispatcherServlet - "ERROR" dispatch for POST "/error", parameters={masked}
2021-03-29 08:43:52 - [http-nio-8082-exec-1] - DEBUG - o.s.w.s.m.m.a.RequestMappingHandlerMapping - Mapped to org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController#error(HttpServletRequest)
2021-03-29 08:43:52 - [http-nio-8082-exec-1] - DEBUG - o.s.w.s.m.m.annotation.HttpEntityMethodProcessor - Using 'application/json', given [*/*] and supported [application/json, application/*+json, application/json, application/*+json]
2021-03-29 08:43:52 - [http-nio-8082-exec-1] - DEBUG - o.s.w.s.m.m.annotation.HttpEntityMethodProcessor - Writing [{timestamp=Mon Mar 29 20:43:52 CST 2021, status=400, error=Bad Request, message=, path=/api/offlineE (truncated)...]
2021-03-29 08:43:52 - [http-nio-8082-exec-1] - DEBUG - org.springframework.web.servlet.DispatcherServlet - Exiting from "ERROR" dispatch, status 400

其实，这个错误九成的原因，就是请求参数和@RequestParam(value = "userName ", required = true) String userName，注解@RequestParam的value值不一样的，我写的就奇葩了，字符串后面加了空格。