@MVC Flash Attribute Support

Option 1: @FlashAttributes

Description:

Attributes present in the model that match the @FlashAttributes annotation are added to flash storage if the controller redirects.

Example:

@Controller
@FlashAttributes("successMessage")
public class MessageController {

	@RequestMapping(value = "/messages", method = RequestMethod.POST)
	public String sendMessage(TestBean testBean, BindingResult result, Model model) {
		if (result.hasErrors()) {
			return "messages/new";
		}
		else {
			model.addAttribute("id", "1").addAttribute("name", "value").addAttribute("successMessage", "yay!");
			return "redirect:/messages/{id}";
		}
	}
}

Advantages:

• There is only one interface for adding attributes of any kind
• Consistent with @SessionAttributes
• Does not require additional method arguments
• Syncs the model transparently

Things to Consider:

• @FlashAttributes may contain a mix of attributes applicable to different redirect scenarios
• A degree of duplication if you need to add a flash attribute and then list it
• It's not obvious if @FlashAttributes means attributes to store or to retrieve? Since @FlashAttributes lists attributes for different redirect scenarios, using the same list to retrieve can become confusing

Option 2: ResponseContext Method Argument

Description:

A ResponseContext method argument provides convenience methods for selecting a view to render and to redirect. Note that for a redirect the implicit model is ignored allowing precise control over the attributes used.

Example:

@Controller
public class MessageController {

	@RequestMapping(value = "/messages", method = RequestMethod.POST)
	public void sendMessage(TestBean testBean, BindingResult result, ResponseContext responseContext) {
		if (result.hasErrors()) {
			responseContext.view("messages/new");
		}
		else {
			responseContext.redirect("redirect:/messages/{id}").uriVariable("id", "1").queryParam("name", "value")
					.flashAttribute("successMessage", "yay!");
		}
	}
}

Advantages:

• Flash attributes can be specified just once (if not already present in the model)
• Precise control over the model on a redirect (SPR-1068, SPR-1294, SPR-6796)

Things to Consider:

• A method must return void and that can only be verified (and flagged as an error) at runtime
• Prevents customizing response handling (HandlerMethodReturnValueHandler, ModelAndViewResolver)
• A degree of duplication when attributes (uri vars, query param, flash attrs) are already in the model
• No clean way of returning a RedirectView or a RedirectView sub-type

Option 3: ResponseInstruction Return Value

Description:

A ResponseInstruction return value is used to select a view to render or to redirect. This is similar to the ResponseContext method argument option but using a return value.

Example:

@Controller
public class MessageController {

	@RequestMapping(value = "/messages", method = RequestMethod.POST)
	public ResponseInstruction sendMessage(TestBean testBean, BindingResult result) {
		if (result.hasErrors()) {
			return new ViewInstruction("messages/new");
		}
		else {
			return new RedirectInstruction("redirect:/messages/{id}").uriVariable("id", "1")
					.queryParam("name", "value").flashAttribute("successMessage", "yay!");
		}
	}
}

Advantages:

• Same as for RedirectContext

Things to Consider:

• More verbose than returning a String view name
• It becomes necessary to use new ViewInstruction("messages/new") without benefit
• No clean way of returning a RedirectView or a RedirectView sub-type

Option 4: RedirectModel Method Argument

Description:

Controller method declares a RedirectModel method argument, which @MVC uses instead of the implicit model if the controller redirects. Initially the redirect model is empty allowing precise control over the attributes used.

Example:

@Controller
public class MessageController {

	@RequestMapping(value = "/messages", method = RequestMethod.POST)
	public String sendMessage(TestBean testBean, BindingResult result, RedirectModel redirectModel) {
		if (result.hasErrors()) {
			return "messages/new";
		}
		else {
			redirectModel.addAttribute("id", "1").addAttribute("name", "value")
					.addFlashAttribute("successMessage", "yay!");
			return "redirect:/messages/{id}";
		}
	}
}

Advantages:

• Flash attributes can be specified just once (if not already present in the model)
• Precise control over the model on a redirect (SPR-1068, SPR-1294, SPR-6796)

Things to Consider:

• Although RedirectModel is a Model, flash attributes aren't treated as other model attributes.
• Having a different kind of model for what is a rendering concern seems backwards.
• A degree of duplication for attribute that are already in the model

Option 5: @RedirectAttributes

Description:

@RedirectAttributes annotation lists attributes to be used if the controller method redirects.

Example:

@Controller
public class MessageController {

	@RequestMapping(value = "/messages", method = RequestMethod.POST)
    @RedirectAttributes(value = {"id", "name"}, flash = "successMessage")
	public String sendMessage(TestBean testBean, BindingResult result, Model model) {
		if (result.hasErrors()) {
			return "messages/new";
		}
		else {
			model.addAttribute("id", "1").addAttribute("name", "value").addAttribute("successMessage", "yay!");
			return "redirect:/messages/{id}";
		}
	}
}

Advantages:

• There is only one interface for adding attributes of any kind
• Does not require additional method arguments
• Precise control over the model on a redirect (SPR-1068, SPR-1294, SPR-6796)
• Syncs the model transparently

Things to Consider:

• A degree of duplication if you need to add a flash attribute and then list it.