问个文件上传的有关问题

问个文件上传的问题
运行到下面这步的时候报了错，请问是什么原因啊
try   {
items   =   upload.parseRequest(request);
          }   catch   (FileUploadException   e1)   {
e1.printStackTrace();
}

java.lang.NoClassDefFoundError:   org/apache/commons/io/output/DeferredFileOutputStream
org.apache.commons.fileupload.disk.DiskFileItemFactory.createItem(DiskFileItemFactory.java:191)
org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:350)
org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:126)
com.ebidding.admin.servlet.UploadTest.doPost(UploadTest.java:36)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)



[解决办法]
java.lang.NoClassDefFoundError:
有個jar包沒有裝好.