ssm中layui上传图片，后台报java.lang.NullPointerException错误

今天在ssm项目中做一个页面的更换图片的功能，用了layui，但是按照layui的文档使用后，可以进入控制类，但是一

直报java.lang.NullPointerException错误，最开始一直以为是layui写的有错误，或者是控制类有错或者参数等有问题，

所以修改调试了好久，但是都没解决，后来在网上看到一个资料觉得可能使配置有问题，试了试后终于解决，因此写

下这篇博客，供自己或者网友参考。

说下最后的解决方案吧：在springMvc的配置文件中的beans下添加了

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">

    <property name="defaultEncoding" value="utf-8"></property>

</bean>

异常如下：

Type Exception Report

Message Request processing failed; nested exception is java.lang.NullPointerException

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:980)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:859)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

Root Cause

java.lang.NullPointerException
	com.gzbd.medicineVender.controller.LoginController.uploadImg(LoginController.java:222)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	java.lang.reflect.Method.invoke(Method.java:498)
	org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:178)
	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:444)
	org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:432)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:968)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:859)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:121)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

Note The full stack trace of the root cause is available in the server logs.