急，jsp上传文件问题？？

[duckcn]

import com.oreilly.servlet.MultipartRequest;

下面这句运行出错
MultipartRequest _upLoadReq = new MultipartRequest(httpServletRequest, ".", 20*1024*1024);

错误：
java.rmi.RemoteException: hookThrowable; nested exception is:
java.io.IOException: Corrupt form data: premature ending
java.io.IOException: Corrupt form data: premature ending
at com.oreilly.servlet.multipart.MultipartParser.(MultipartParser.java:205)
at com.oreilly.servlet.MultipartRequest.(MultipartRequest.java:222)
at com.oreilly.servlet.MultipartRequest.(MultipartRequest.java:109)
......

不知道什么原因？

[study_body]

http://groups.google.com/groups?q=java.io.IOException:+Corrupt+form+data:+premature+ending&hl=zh-CN&lr=&ie=UTF-8&inlang=zh-CN&selm=3e28533d%241%40newsgroups.bea.com&rnum=3