报错信息：
HTTP Status 500 - Servlet.init() for servlet servlet-name threw exception
详细报错内容：
type Exception report
message Servlet.init() for servlet FileUpload threw exception
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: Servlet.init() for servlet FileUpload threw exception
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
root cause
java.lang.NoClassDefFoundError: org/apache/commons/fileupload/FileItemFactory
java.lang.Class.getDeclaredMethods0(Native Method)
java.lang.Class.privateGetDeclaredMethods(Class.java:2688)
java.lang.Class.getDeclaredMethods(Class.java:1962)
org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:571)
org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:490)
org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:474)
org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.determineCandidateConstructors(AutowiredAnnotationBeanPostProcessor.java:241)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineConstructorsFromBeanPostProcessors(AbstractAutowireCapableBeanFactory.java:1059)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1032)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:505)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302)
org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:229)
org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298)
org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:725)
org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:629)
org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:677)
org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:548)
org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
javax.servlet.GenericServlet.init(GenericServlet.java:158)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
root cause
java.lang.ClassNotFoundException: org.apache.commons.fileupload.FileItemFactory
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
java.lang.Class.getDeclaredMethods0(Native Method)
java.lang.Class.privateGetDeclaredMethods(Class.java:2688)
java.lang.Class.getDeclaredMethods(Class.java:1962)
org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:571)
org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:490)
org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:474)
org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.determineCandidateConstructors(AutowiredAnnotationBeanPostProcessor.java:241)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineConstructorsFromBeanPostProcessors(AbstractAutowireCapableBeanFactory.java:1059)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1032)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:505)
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:302)
org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:229)
org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:298)
org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:725)
org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:629)
org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:677)
org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:548)
org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
javax.servlet.GenericServlet.init(GenericServlet.java:158)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.lang.Thread.run(Thread.java:745)
遇到这个报错时，先检查是否缺少jar：commons-fileupload.jar和commons-io.jar
commons-fileupload
commons-fileupload
1.3.2
pom文件中引入上面的依赖默认commons-fileupload.jar和commons-io.jar这两个jar都会download。