parseRequest(request)类型不匹配问题

在写菜鸟教程上的Servlet文件上传的demo时，突然报错。

List<FileItem> formItems = upload.parseRequest((RequestContext) request);

必须把request强制转换，跟样例代码有些不一样，先测试。
上传一个.txt文件后，并没有出现上传成功的字样。

回到eclipse，报错信息。

java.lang.ClassCastException: org.apache.catalina.connector.RequestFacade cannot be cast to org.apache.tomcat.util.http.fileupload.RequestContextat com.runoob.test.UploadServlet.doPost(UploadServlet.java:95)at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Thread.java:748)

重点是在第一行的类型不匹配。
反复对比样例代码，一模一样的代码为什么会报错。
记得在编写代码前的一个重要的导包工作，如果不先导包，那默认的导入的包是错误的。

import org.apache.tomcat.util.http.fileupload.FileItem; 
import org.apache.tomcat.util.http.fileupload.FileUploadException; 
import org.apache.tomcat.util.http.fileupload.disk.DiskFileItemFactory; 
import org.apache.tomcat.util.http.fileupload.servlet.ServletFileUpload;

正确的应该是：

import org.apache.commons.fileupload.FileItem; 
import org.apache.commons.fileupload.FileUploadException; 
import org.apache.commons.fileupload.disk.DiskFileItemFactory; 
import org.apache.commons.fileupload.servlet.ServletFileUpload; 

所以应该提前导入

修改导入的包后，上传文件成功。