I downloaded the code for the Spring MVC 3 Showcase. One thing puzzles me (well, more than one), why does this (edited for concision) sample return null?
#Controller
#RequestMapping("/form")
public class FormController {
#RequestMapping(method=RequestMethod.POST)
public String processSubmit(#Valid FormBean form,
BindingResult result,
WebRequest webRequest,
HttpSession session, Model model) {
if (result.hasErrors()) {
return null;
} else {
session.setAttribute("form", form);
return "redirect:/form";
}
}
}
If a controller returns a null view name, or declares a void return type, Spring will attempt to infer the view name from the request URL.
In your case, it will assume the view name is form, and proceed on that assumption.
It does this using an implementation of RequestToViewNameTranslator, the default implementation of which is DefaultRequestToViewNameTranslator, the javadoc for which explains the exact rules it applies.
AnnotationMethodHandlerAdapter.invokeHandlerMethod() takes care of invoking handler methods. Here, a ModelAndView will be retrieved via ServletHandlerMethodInvoker.getModelAndView().
In your case, getModelAndView() gets provided the handler method's null return value. The getModelAndView() method checks for the return value's type, but as in Java null is never an instanceof any class, that method's logic will create a new ModelAndView. A new ModelAndView has initially its view property set to null.
Then later back up the call stack, in DispatcherServlet.doDispatch(), there is a test if the ModelAndView object has a View associated with it ( mv.hasView() ). Because view == null, doDispatch()'s logic calls mv.setViewName(getDefaultViewName(request)). It delegates to the registered RequestToViewNameTranslator, whose default implementation is DefaultRequestToViewNameTranslator. This subclass translates the request URI into a view name, in your case form.
Later in doDispatch(), via render() -> resolveViewName(), this sample's ViewResolvers are provided with the view name form. Only one ViewResolver, InternalResourceViewResolver is used in this sample. Also, this InternalResourceViewResolver was configured in src/main/webapp/WEB-INF/spring/appServlet/servlet-context.xml to add the prefix /WEB-INF/views/ and the suffix .jsp to the view name. So in total, it will create a View using the JSP file /WEB-INF/views/form.jsp. Luckily, a JSP file exists at exactly this location.
Related
Having this handler method:
#RequestMapping(method = RequestMethod.POST, value = "/myform1")
public String formPost(#ModelAttribute("myModel") #Valid MyModel myModel, BindingResult binder)
how can I ignore errors on certain (or all) fields?
Even if I omit the #Valid annotation, it still detects errors like "abc entered into a Number field" (ie binder.hasErrors() returns true). And the the error message (from the catalog) is displayed on the final web page, which I do not want.
If I omit the BindingResult binder, then the code never reaches this method but throws an exception/error before it.
Is there a #DontValidateAtAll annotation or some other method to achieve this?
Related problem: I can not override the bad value in the method, it keeps showing the old rejected value. For example, user enters "abc" into myModel.someNumber and submits the form, then even if I do myModel.setSomeNumber(22) in the method formPost(), after returning from it, the web page (JSP) will show "abc" (and the error text) instead of 22 in that field.
For the specific String-to-Number conversion exception you were referring to, you can use the below manipulation. This is a type conversion exception that occurs even before Spring MVC's form validation, ie, even before the validate() method.
If your only purpose is to NOT see the errors on your final web page, then you can write extra code in your Controller method.
#RequestMapping(method = RequestMethod.POST, value = "/myform1")
public ModelAndView formPost(#ModelAttribute("myModel") #Valid MyModel myModel, BindingResult binder){
List<ObjectError> errors = bindingResult.getAllErrors();
boolean hasIgnorableErrorsOnly = true;
if(bindingResult.hasErrors()){
for(ObjectError error : errors){
if(error.getCode().equals("myModel.someNumber.NotANumber")){ //or whatever your error code is
}else{
hasIgnorableErrorsOnly = false;
}
}
}
if(hasIgnorableErrorsOnly){
//You have not shown where your final view is. I am assuming your myModel form view is myform.jsp and final web page is myModel.jsp
// Notice that I have also changed this method signature to return ModelAndView instead of only String view.
if(myModel.getSomeNumber() == null)
myModel.setSomeNumber(22);
return new ModelAndView("myModel.jsp", myModel); //Take care of view Resolvers here
}else{
return new ModelAndView("myform.jsp", myModel); //Take care of view Resolvers here
}
}
Now, if your BindingResult has more than ignorable errors, then it would go to myModel.jsp and I believe you already have code in place for display of errors. But if, because of above code, you are forwarded to myModel.jsp, you would have to iterate over the ${errors} key on your jsp and write the someNumber element so that it does not show errors. For example,
<spring:hasBindErrors name="myModel">
<c:forEach items="${errors.allErrors}" var="error">
<c:if test="${error.code eq 'myModel.someNumber.NotANumber'}">
//skip your display of global errors
</c:if>
</c:forEach>
</spring:hasBindErrors>
This works:
add a (Model)Map parameter to the handler method (it is usually used anyway, I omitted it in the question for brevity)
overwrite the model attribute with a fresh copy
Code:
#RequestMapping(method = RequestMethod.POST, value = "/myform1")
public String formPost(#ModelAttribute("myModel") #Valid MyModel myModel, BindingResult binder, Map<String, Object> modmap) {
if(ignore_errors) {
modmap.put("myModel", new MyModel());
return "myForm.jsp";
} // else ... other things
}
Apparently this procedure makes the framework to "forget" about the validation errors.
Note: I use Spring 3.0.x, other versions might behave differently.
I am using Spring MVC and Hibernate in my project. Also I have 2 controllers UserController and BookController where BookController redirects to the users page and I am passing a Book object in addition.
I've found I can do this with RedirectAttributes but the problem is that the id of the passed Book object is changed during this transition to user.id.
BookController.java
public class BookController {
#RequestMapping("/users/{user_id}/books/edit/{book_id}")
public String editBook(#PathVariable("user_id") int user_id, #PathVariable("book_id") int book_id, final RedirectAttributes redirectAttrs){
bookDetail = this.bookService.getBookById(book_id)
redirectAttrs.addFlashAttribute("bookDetail", bookDetail);
System.out.println(bookDetail);
return "redirect:/users/"+user_id;
}
}
Prints: id=8, title=Motylek, description=Some description, user_id=2.
UserController.java
public class UserController {
#RequestMapping("/users/{id}")
public String detailUser(#ModelAttribute("bookDetail") Book bookDetail, #PathVariable("id") int id, Model model){
User u = this.userService.getUserById(id);
model.addAttribute("user", u);
model.addAttribute("bookDetail", bookDetail);
System.out.println(bookDetail);
return "user";
}
}
Prints: id=2, title=Motylek, description=Some description, user_id=2.
Do you have and idea why this happens or is it a bug? Thanks.
I'm going to assume that your Book class has a property called id, ie. a getter or setter called getId() and setId(..).
When Spring parses the request URL, it stores path segments as declared in the corresponding #RequestMapping. So for
/your-app/users/2
and
#RequestMapping("/users/{id}")
It will store
id=2
as a request parameter.
Spring will then proceed to generate an argument for
#ModelAttribute("bookDetail") Book bookDetail
It will check the various request, session, servlet attributes for an entry with the name bookDetail. (If it doesn't find one, it will create one and add it to the request attributes.) In your case, it will have found the object in the HttpSession. It will then bind any request parameters to matching object properties. Since the parameter above is called id, it will be bound to the Book property id.
You should be good by changing
#RequestMapping("/users/{id}")
to
#RequestMapping("/users/{user_id}")
along with the corresponding #PathVariable.
I have a spring MVC based web application. Currently in my web page i am showing the user first name and last name after user logs in. The way i am doing this is, for every HttpServletRequest that comes into #Controller#RequestMapping, i get the Principal object and get the user details from it, then populate the ModelMap with firstname and lastname attribute. For example here is the sample code
#Autowired
private SecurityDetails securityDetails;
#RequestMapping(method = RequestMethod.GET)
public String showWelcomePage(HttpServletRequest request,
HttpServletResponse response, ModelMap model, Principal principal)
{
securityDetails.populateUserName(model, principal);
... lot of code here;
return "home";
}
public boolean populateUserName(ModelMap model, Principal principal) {
if (principal != null) {
Object ob = ((Authentication)principal).getPrincipal();
if(ob instanceof MyUserDetails)
{
MyUserDetails ud = (MyUserDetails)ob;
model.addAttribute("username", ud.getFirstName() + " " + ud.getLastName());
}
return true;
}
else
{
logger.debug("principal is null");
return false;
}
}
My problem is i am having to call the populateUserName method for every RequestMapping. Is there a elegant way, like populating this in Interceptor method, which will result in this method being called just in one place for entire application?
Its good that you want to prevent duplication of code. Here is how you can do it.
Create a custom HandlerInterceptor http://static.springsource.org/spring/docs/2.5.x/api/org/springframework/web/servlet/HandlerInterceptor.html
Post handle is the only method of interest for us, for the others return defaults.
In the post handle method, you have access to the model and view returned from your controller, go ahead and add whatever you want.
The Principal will not be available directly here, you will have to look it up using some code like SecurityContextHolder.getContext().getAuthentication().getPrincipal()
Wire the handler interceptor to intercept all or some of your controllers.
Hope this helps.
You can use either Servlet Filters or Spring Interceptors.
BTW, where do you populate the Principal from?
In any case, thats where you should do this populating stuff.
Here is one of the examples that I've seen on how to do validation on Controller:
[HttpPost]
public ViewResult Create(MyModel response)
{
if (ModelState.IsValid)
{
return View("Thanks");
}
else
{
return View();
}
}
If there are validation errors, than return View() method is called without any parameters. Obviously you have #Html.ValidationSummary() in your View and Model has all required property attributes.
The data that was entered into the form was preserved and displayed again when the view was rendered with the validation summary.
My question: how is the data preserved? Since it was not passed to the View like
return View(response);
Thanks a lot.
Sincerely,
Vlad
It is because the values have been bound to the model state which is passed back along to the view. This is along the same issue/question on why you cannot change a model value and return the view again. Meaning, let's assume I have the following property on my Viewmodel
public string Name {get;set;}
Using the controller below, I cannot change the ViewModel property without also either clearing the ModelState or updating the value in the model state. Try it!
[HttpPost]
public ViewResult Create(MyModel response)
{
response.Name = response.Name + "Some Random String"
return View();
}
The name property will remain unchanged. Essentially, once the ModelBinding occurs, the values from your form (ViewModel) are bound to the model state, which is why you do not have to pass the model back to the view.
As a side note, I always pass the model back in my call to return View();, it just seems more correct and a little easier to read
On ASP.NET MVC 3, assume that we have following controller action:
public ActionResult Index() {
ViewBag.Message = "Foo Bar";
return View();
}
Here, Index method is returning ViewResult instance which implements System.Web.Mvc.ViewResultBase class. Because of the fact that we return instance of a ViewResult class, system tries to find a proper view file in order to generate an output. If it cannot find it, it will throw an exception.
My question is this:
Is there any other base class which looks for a view other than System.Web.Mvc.ViewResultBase?
In plain English, do we have to return a class, which implements System.Web.Mvc.ViewResultBase class, from controller action in order to render the result with a view?
EDIT
Also, as you see here I am telling that I will return a type of ActionResult which is the base, base class so to speak. When you look at the end, I am returning an instance of ViewResult.
How does framework handle that? Does it try to cast every controller action result to ViewResultBase class on the fly? I am really curious about this part especially.
The ControllerActionInvoker class is responsible for executing the controller actions. After finding and executing the action it looks for the action return type:
If the return type is void then it the creates a EmptyResult
If the return type anything but ActionResult then it converts the returned value to string and creates a ContentResult with that string.
So finally a result of an action is always an instance of the ActionResult class which declares the following method:
public abstract void ExecuteResult(ControllerContext context);
Then the ControllerActionInvoker basically calls this ExecuteResult method to allow for the ActionResult to write to the Reponse. There is where in the case of ViewResultBase the view rendering is happening.
To answer your fist question in MVC3 only the descandants of the ViewResultBase class are rendering views.