[29.10.07 9:31:11:562 MSK] 00000041 ServletWrappe E   SRVE0068E: Could not invoke the service() method on servlet ImportPensData. Exception thrown : java.lang.NoClassDefFoundError: org/apache/commons/io/output/DeferredFileOutputStream

<?xml version="1.0" encoding="UTF-8"?>
<classpath>
	<classpathentry kind="src" path="JavaSource"/>
	<classpathentry kind="con" path="com.ibm.wtp.server.java.core.container/com.ibm.ws.ast.st.runtime.core.runtimeTarget.v60/WebSphere Application Server v6.0"/>
	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/WebSphere v6 JRE"/>
	<classpathentry kind="lib" path="WebContent/WEB-INF/lib/commons-fileupload-1.2.jar"/>
	<classpathentry kind="lib" path="WebContent/WEB-INF/lib/commons-io-1.3.2.jar"/>
	<classpathentry kind="output" path="WebContent/WEB-INF/classes"/>
</classpath>

...

 import  org.apache.commons.fileupload.FileItem;
 import  org.apache.commons.fileupload.FileItemFactory;
 import  org.apache.commons.fileupload.FileUploadException;
 import  org.apache.commons.fileupload.disk.DiskFileItemFactory;
 import  org.apache.commons.fileupload.servlet.ServletFileUpload;
 import  org.apache.commons.io.output.DeferredFileOutputStream;

 public   class  ImportPensData  extends  HttpServlet  implements  Servlet {
    
     protected   void  doPost(HttpServletRequest req, HttpServletResponse resp)  throws  ServletException, IOException {
        //		 Check that we have a file upload request
		 boolean  isMultipart = ServletFileUpload.isMultipartContent(req);
//		 Create a factory for disk-based file items
		
		FileItemFactory factory =  new  DiskFileItemFactory();
//		 Create a new file upload handler
		ServletFileUpload upload =  new  ServletFileUpload(factory);

        DeferredFileOutputStream dfos =  null ; //  Объявляем dfos для демонстрации, что класс виден       

         try  {
			//		 Parse the request
			List items = upload.parseRequest(req); // А вот здесь класс DeferredFileOutputStream уже не виден
//			 Process the uploaded items
			...
        }  catch  (FileUploadException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
		
      	resp.sendRedirect("DataPage");
	}

}

         try  {
			//		 Parse the request
			List items = upload.parseRequest(req); // А вот здесь класс DeferredFileOutputStream уже не виден
//			 Process the uploaded items
			...
        }  catch  (FileUploadException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}	

[31.10.07 9:24:18:844 MSK] 00000040 WebApp        E   SRVE0026E: [Servlet Error]-[ImportPensData]: java.lang.NoClassDefFoundError: org/apache/commons/io/output/DeferredFileOutputStream
	at org.apache.commons.fileupload.disk.DiskFileItemFactory.createItem(DiskFileItemFactory.java:191)
	at org.apache.commons.fileupload.FileUploadBase.parseRequest(FileUploadBase.java:350)
	at org.apache.commons.fileupload.servlet.ServletFileUpload.parseRequest(ServletFileUpload.java:126)
	at com.pfrkomi.penstransit.ImportPensData.doPost(ImportPensData.java:48)

Why is NoClassDefFoundError being thrown? 

There are two common causes for this error. 

Firstly, it might simply mean that you do not have the Commons IO jar in your classpath. FileUpload depends on IO (see dependencies) - you can tell if this is the case if the missing class is within the org.apache.commons.io package. 

Secondly this happens when attempting to rely on a shared copy of the Commons FileUpload jar file provided by your web container. The solution is to include the FileUpload jar file as part of your own web application, instead of relying on the container. The same may hold for FileUpload's IO dependency.