simpleformcontroller.java

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	 * <p>Default implementation delegates to referenceData(request).
	 * Subclasses can override this to set reference data used in the view.
	 * @param request current HTTP request
	 * @param command form object with request parameters bound onto it
	 * @param errors validation errors holder
	 * @return a Map with reference data entries, or null if none
	 * @throws Exception in case of invalid state or arguments
	 * @see ModelAndView
	 */
	protected Map referenceData(HttpServletRequest request, Object command, Errors errors) throws Exception {
		return referenceData(request);
	}

	/**
	 * Create a reference data map for the given request.
	 * Called by referenceData version with all parameters.
	 * <p>Default implementation returns null.
	 * Subclasses can override this to set reference data used in the view.
	 * @param request current HTTP request
	 * @return a Map with reference data entries, or null if none
	 * @throws Exception in case of invalid state or arguments
	 * @see #referenceData(HttpServletRequest, Object, Errors)
	 * @see ModelAndView
	 */
	protected Map referenceData(HttpServletRequest request) throws Exception {
		return null;
	}


	/**
	 * This implementation calls <code>showForm</code> in case of errors,
	 * and delegates to <code>onSubmit</code>'s full version else.
	 * <p>This can only be overridden to check for an action that should be executed
	 * without respect to binding errors, like a cancel action. To just handle successful
	 * submissions without binding errors, override one of the <code>onSubmit</code>
	 * methods or <code>doSubmitAction</code>.
	 * @see #showForm(HttpServletRequest, HttpServletResponse, BindException)
	 * @see #onSubmit(HttpServletRequest, HttpServletResponse, Object, BindException)
	 * @see #onSubmit(Object, BindException)
	 * @see #onSubmit(Object)
	 * @see #doSubmitAction(Object)
	 */
	protected ModelAndView processFormSubmission(
			HttpServletRequest request, HttpServletResponse response, Object command, BindException errors)
			throws Exception {

		if (errors.hasErrors() || isFormChangeRequest(request)) {
			if (logger.isDebugEnabled()) {
				logger.debug("Data binding errors: " + errors.getErrorCount());
			}
			return showForm(request, response, errors);
		}
		else {
			logger.debug("No errors -> processing submit");
			return onSubmit(request, response, command, errors);
		}
	}

	/**
	 * Determine whether the given request is a form change request.
	 * A form change request changes the appearance of the form
	 * and should always show the new form, without validation.
	 * <p>Gets called by suppressValidation and processFormSubmission.
	 * Consequently, this single method determines to suppress validation
	 * <i>and</i> to show the form view in any case.
	 * @param request current HTTP request
	 * @return whether the given request is a form change request
	 * @see #suppressValidation
	 * @see #processFormSubmission
	 */
	protected boolean isFormChangeRequest(HttpServletRequest request) {
		return false;
	}

	/**
	 * This implementation delegates to <code>isFormChangeRequest</code>:
	 * A form change request changes the appearance of the form
	 * and should not get validated but just show the new form.
	 * @see #isFormChangeRequest
	 */
	protected boolean suppressValidation(HttpServletRequest request) {
		return isFormChangeRequest(request);
	}


	/**
	 * Submit callback with all parameters. Called in case of submit without errors
	 * reported by the registered validator, or on every submit if no validator.
	 * <p>Default implementation delegates to onSubmit(Object, BindException).
	 * For simply performing a submit action and rendering the specified success view,
	 * consider implementing doSubmitAction rather than an onSubmit version.
	 * <p>Subclasses can override this to provide custom submission handling like storing
	 * the object to the database. Implementations can also perform custom validation and
	 * call showForm to return to the form. Do <i>not</i> implement multiple onSubmit
	 * methods: In that case, just this method will be called by the controller.
	 * <p>Call <code>errors.getModel()</code> to populate the ModelAndView model
	 * with the command and the Errors instance, under the specified command name,
	 * as expected by the "spring:bind" tag.
	 * @param request current servlet request
	 * @param response current servlet response
	 * @param command form object with request parameters bound onto it
	 * @param errors Errors instance without errors (subclass can add errors if it wants to)
	 * @return the prepared model and view, or null
	 * @throws Exception in case of errors
	 * @see #onSubmit(Object, BindException)
	 * @see #doSubmitAction
	 * @see #showForm
	 * @see org.springframework.validation.Errors
	 * @see org.springframework.validation.BindException#getModel
	 */
	protected ModelAndView onSubmit(
			HttpServletRequest request,	HttpServletResponse response, Object command,	BindException errors)
			throws Exception {
		return onSubmit(command, errors);
	}

	/**
	 * Simpler onSubmit version. Called by the default implementation of the onSubmit
	 * version with all parameters.
	 * <p>Default implementation calls onSubmit(command), using the returned ModelAndView
	 * if actually implemented in a subclass. Else, the default behavior is applied:
	 * rendering the success view with the command and Errors instance as model.
	 * <p>Subclasses can override this to provide custom submission handling that
	 * does not need request and response.
	 * <p>Call <code>errors.getModel()</code> to populate the ModelAndView model
	 * with the command and the Errors instance, under the specified command name,
	 * as expected by the "spring:bind" tag.
	 * @param command form object with request parameters bound onto it
	 * @param errors Errors instance without errors
	 * @return the prepared model and view, or null
	 * @throws Exception in case of errors
	 * @see #onSubmit(HttpServletRequest, HttpServletResponse, Object, BindException)
	 * @see #onSubmit(Object)
	 * @see #setSuccessView
	 * @see org.springframework.validation.Errors
	 * @see org.springframework.validation.BindException#getModel
	 */
	protected ModelAndView onSubmit(Object command, BindException errors) throws Exception {
		ModelAndView mv = onSubmit(command);
		if (mv != null) {
			// simplest onSubmit version implemented in custom subclass
			return mv;
		}
		else {
			// default behavior: render success view
			if (getSuccessView() == null) {
				throw new ServletException("successView isn't set");
			}
			return new ModelAndView(getSuccessView(), errors.getModel());
		}
	}

	/**
	 * Simplest onSubmit version. Called by the default implementation of the
	 * onSubmit version with command and BindException parameters.
	 * <p>This implementation calls <code>doSubmitAction</code> and returns null
	 * as ModelAndView, making the calling onSubmit method perform its default
	 * rendering of the success view.
	 * <p>Subclasses can override this to provide custom submission handling
	 * that just depends on the command object. It's preferable to use either
	 * <code>onSubmit(command, errors)</code> or <code>doSubmitAction(command)</code>,
	 * though: Use the former when you want to build your own ModelAndView; use the
	 * latter when you want to perform an action and forward to the successView.
	 * @param command form object with request parameters bound onto it
	 * @return the prepared model and view, or null for default (i.e. successView)
	 * @throws Exception in case of errors
	 * @see #onSubmit(Object, BindException)
	 * @see #doSubmitAction
	 * @see #setSuccessView
	 */
	protected ModelAndView onSubmit(Object command) throws Exception {
		doSubmitAction(command);
		return null;
	}

	/**
	 * Template method for submit actions. Called by the default implementation
	 * of the simplest onSubmit version.
	 * <p><b>This is the preferred submit callback to implement if you want to
	 * perform an action (like storing changes to the database) and then render
	 * the success view with the command and Errors instance as model.</b>
	 * You don't need to care about the success ModelAndView here.
	 * @param command form object with request parameters bound onto it
	 * @throws Exception in case of errors
	 * @see #onSubmit(Object)
	 * @see #setSuccessView
	 */
	protected void doSubmitAction(Object command) throws Exception {
	}

}