import org.apache.commons.fileupload.FileUploadBase.FileSizeLimitExceededException; //导入依赖的package包/类
/**
 * Add a file skipped message notification for action messages.
 *
 * @param fileName file name
 * @param request the servlet request
 */
private void addFileSkippedError(String fileName, HttpServletRequest request) {
    String exceptionMessage = "Skipped file " + fileName + "; request size limit exceeded.";
    FileSizeLimitExceededException exception = new FileUploadBase.FileSizeLimitExceededException(exceptionMessage, getRequestSize(request), maxSize);
    String message = buildErrorMessage(exception, new Object[]{fileName, getRequestSize(request), maxSize});
    if (!errors.contains(message)) {
        errors.add(message);
    }
}
 

import org.apache.commons.fileupload.FileUploadBase.FileSizeLimitExceededException; //导入依赖的package包/类
/**
 * Allows to handle the file upload exceptions and to write them into the output
 * stream so that the client will be able to deserelize them and to show to the user.
 * @param logger the logger object
 * @param ex the exception that has happened
 * @param response the servlet responce
 * @param max_img_size_bytes the mazimum size dor the uploaded image
 * @throws IOException if smth bad happens
 */
public static void handleFileUploadExceptions(Logger logger, FileUploadException ex, HttpServletResponse response,
												final long max_img_size_bytes ) throws IOException {
	String errorCode = "";
	if( ex instanceof IOFileUploadException ) {
		//Thrown to indicate an IOException
		logger.error( "An IOException exception while user-file upload." , ex);
		errorCode += ExceptionsSerializer.serialize( new InternalSiteException(InternalSiteException.IO_FILE_UPLOAD_EXCEPTION_ERR ) );
	} else if( ex instanceof InvalidContentTypeException ) {
		//Thrown to indicate that the request is not a multipart request. 
		logger.error( "An incorrect request while user-file upload." , ex);
		errorCode += ExceptionsSerializer.serialize( new InternalSiteException(InternalSiteException.INCORRECT_FILE_UPLOAD_REQUEST_EXCEPTION_ERR ) );
	} else if( ex instanceof FileSizeLimitExceededException ) {
		//Thrown to indicate that A files size
		//exceeds the configured maximum.
		logger.warn( "File size exceeded while user-file upload" );
		errorCode += ExceptionsSerializer.serialize( new UserFileUploadException( UserFileUploadException.FILE_IS_TOO_LARGE_ERR ) );
	} else if( ex instanceof SizeLimitExceededException ){
		//Thrown to indicate that the request size
		//exceeds the configured maximum.
		logger.warn( "Request size exceeded while user-file upload" );
		UserFileUploadException nex = new UserFileUploadException( UserFileUploadException.FILE_IS_TOO_LARGE_ERR );
		nex.setMaxUploadFileSize( max_img_size_bytes );
		errorCode += ExceptionsSerializer.serialize( nex );
	} else {
		//Some unknown exceptions, there should not be any else left, but just in case ...
		logger.error( "An unknown exception while user-file upload", ex);
		errorCode += ExceptionsSerializer.serialize( new InternalSiteException(InternalSiteException.UNKNOWN_INTERNAL_SITE_EXCEPTION_ERR ) );
	}
	response.getWriter().println( errorCode );
}