在 JSP 测试 文件上传时，报错如下：
Type 异常报告
消息 Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: org/apache/commons/io/IOUtils
描述 服务器遇到一个意外的情况，阻止它完成请求。
Exception
org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: org/apache/commons/io/IOUtils
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1006)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
Root Cause
java.lang.NoClassDefFoundError: org/apache/commons/io/IOUtils
org.apache.commons.fileupload.util.Streams.copy(Streams.java:123)
org.apache.commons.fileupload.util.Streams.copy(Streams.java:70)
org.apache.commons.fileupload.MultipartStream.readBodyData(MultipartStream.java:593)
org.apache.commons.fileupload.MultipartStream.discardBodyData(MultipartStream.java:617)
org.apache.commons.fileupload.MultipartStream.skipPreamble(MultipartStream.java:634)
org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.findNextItem(FileUploadBase.java:1023)
org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.<init>(FileUploadBase.java:1003)
org.apache.commons.fileupload.FileUploadBase.getItemIterator(FileUploadBase.java:310)
org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:334)
org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:115)
org.springframework.web.multipart.commons.CommonsMultipartResolver.parseRequest(CommonsMultipartResolver.java:157)
org.springframework.web.multipart.commons.CommonsMultipartResolver.resolveMultipart(CommonsMultipartResolver.java:141)
org.springframework.web.servlet.DispatcherServlet.checkMultipart(DispatcherServlet.java:1128)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:960)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
Root Cause
java.lang.ClassNotFoundException: org.apache.commons.io.IOUtils
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1358)
org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1180)
org.apache.commons.fileupload.util.Streams.copy(Streams.java:123)
org.apache.commons.fileupload.util.Streams.copy(Streams.java:70)
org.apache.commons.fileupload.MultipartStream.readBodyData(MultipartStream.java:593)
org.apache.commons.fileupload.MultipartStream.discardBodyData(MultipartStream.java:617)
org.apache.commons.fileupload.MultipartStream.skipPreamble(MultipartStream.java:634)
org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.findNextItem(FileUploadBase.java:1023)
org.apache.commons.fileupload.FileUploadBase$FileItemIteratorImpl.<init>(FileUploadBase.java:1003)
org.apache.commons.fileupload.FileUploadBase.getItemIterator(FileUploadBase.java:310)
org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:334)
org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:115)
org.springframework.web.multipart.commons.CommonsMultipartResolver.parseRequest(CommonsMultipartResolver.java:157)
org.springframework.web.multipart.commons.CommonsMultipartResolver.resolveMultipart(CommonsMultipartResolver.java:141)
org.springframework.web.servlet.DispatcherServlet.checkMultipart(DispatcherServlet.java:1128)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:960)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:881)
javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855)
javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
解决办法：
1.查看target下的WEB-INF的lib文件夹下面有没有 commons-io 这个jar包，果然没有，应该是主动导包没有成功。
2. 修改 pom.xml 中 commons-io 依赖的版本，我是 2.4 改为了 2.3，然后删除target文件夹，接着rebuild。
3. 这时候发现target下的WEB-INF的lib文件夹下面有 commons-io 这个jar包了，运行也成功。
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