求助：上传问题！

int maxPostSize = 3 * 5 * 1024 * 1024; // 每个文件最大5MB,最多3个文件
// response的编码为"UTF-8"
MultipartRequest multi;
String saveDirectory = request.getSession().getServletContext().getRealPath("/")+"upload";
String fileName = null;
int rowNum = 0; try {
// 上传 
RandomFileRenamePolicy rfrp = new RandomFileRenamePolicy();
multi = new MultipartRequest(request, saveDirectory, maxPostSize,
"utf-8", rfrp);
// 输出反馈信息
Enumeration files = multi.getFileNames();
while (files.hasMoreElements()) {
String name = (String) files.nextElement();
File f = multi.getFile(name);
if (f != null) {
fileName = multi.getFilesystemName(name); }
}
出现以下异常：
java.io.IOException: Corrupt form data: premature ending
at com.oreilly.servlet.multipart.MultipartParser.<init>(MultipartParser.java:205)
at com.oreilly.servlet.MultipartRequest.<init>(MultipartRequest.java:222)
at com.longsun.lmsell.web.action.EquipmentAction.doAddByExcel(EquipmentAction.java:172)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:269)
at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:170)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:462)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Unknown Source)