springmvc文件上传报错

学习spring mvc的文件上传，在上传的时候遇到一下错误：

HTTP Status 500 - Request processing failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [org.springframework.web.multipart.commons.CommonsMultipartFile]: No default constructor found; nested exception is java.lang.NoSuchMethodException: org.springframework.web.multipart.commons.CommonsMultipartFile.()

exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.beans.BeanInstantiationException: 

Could not instantiate bean class [org.springframework.web.multipart.commons.CommonsMultipartFile]:

 No default constructor found; nested exception is java.lang.NoSuchMethodException: org.springframework.web.multipart.commons.CommonsMultipartFile.()
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:943)
	org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:833)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:807)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)

翻译过来就是就是说找不到默认的构造方法。查阅官方文档，发现了和自己写的代码不一致的地方是少了一个@RequestParam("file")的注解。加上之后正常运行。所以，在文件上传时，一定要加上@RequestParam("file")这个注解，无论你的参数名是否和表单是不是相同。