??? Large Objects may not be used in auto-commit mode

[MaxMan]

Finally, I got a nice working solution after having a more detailed look on the stack trace. Saves everything in a transaction:

	@Autowired
	private ConversionService conversionService;
	@Autowired  
	private Validator validator;

	...

	@RequestMapping(method = RequestMethod.POST)
	@Transactional
	public String edit(@PathVariable("type") final String type,
			Model model, HttpServletRequest req)
			throws Exception {
		// retrieve command object
		Object entity = getCommand(type, req);
		// validate and bind request data, manually
		ServletRequestDataBinder binder = new ServletRequestDataBinder(entity);
		binder.setConversionService(conversionService);
		binder.setValidator(validator);
		binder.bind(req);
		binder.validate();
		BindingResult result = binder.getBindingResult();
		if (model!=null)
			// publish BindingResult in model
			model.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, result);
		// do save entity or display error
		Long id = getId(entity);
		if (result.hasErrors()) { // validation failed
			prepareModel(model, type, type + (id==null ? ".create" : ".update"), entity);
			return getViewName(type, "edit");
		}
		// save entity
		if (id==null)
			facade.create(entity);
		else
			facade.edit(entity);
		return "redirect:/system/" + type + "/"
				+ encodeUrlPathSegment(getId(entity).toString(), req)
				+ "/edit";
	}

	...