ZK - Open Source Ajax Java Framework

package test; 

import org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException;
import org.zkoss.zk.au.http.AuUploader; 

public class MyUploader extends AuUploader { 

protected String handleError(Throwable ex) { 
if(ex instanceof SizeLimitExceededException){ 
SizeLimitExceededException e = (SizeLimitExceededException) ex; 
return e.getActualSize() + " is over our limit"; 
} 
return super.handleError(ex); 
}
}

2. Apply it in the web.xml


<servlet> 
<description>The asynchronous update engine for ZK</description> 
<servlet-name>auEngine</servlet-name> 
<servlet-class>org.zkoss.zk.au.http.DHtmlUpdateServlet</servlet-class> 
<init-param> 
<param-name>extension0</param-name> 
<param-value>/upload=test.MyUploader</param-value> 
</init-param>
</servlet>