I have a Controller with the following method:
#RequestMapping(method = POST)
public ModelAndView emailRegister(EmailParameter parameters, ModelMap model) {}
Where EmailParameter is an interface. I understand Spring (magically?) maps the incoming HTTP parameters to my object fields by name, and it can't do this as I have declared an Interface.
Is it possible to declare an interface here, if so is there additional config I need somewhere?
I don't have extensive programming experience so I may be wrong in trying to use an Interface type here, but I believe this is what I should be doing?
Additionally if someone could explain how Spring maps the request parameters to my object fields, that would be much appreciated. Or a link to where this is explained, as I haven't been able to find one!
Thanks
You shouldn't use Interface because Spring needs to instantiate that object, otherwise you will be requiring the property editors OR converters.
Read the following post to know about How Spring MVC Binds Parameter?
Read section "Binding Domain Object" in following link.
https://web.archive.org/web/20160516151809/http://www.jpalace.org/document/92/binding-and-validation-of-handler-parameters-in-spring-mvc-controllers
Related
If I use Spring, which of these two methods is more correct.
Can I use the new() operator even if I use dipendency injection?.Can I mix both?
I would like to have some clarification on these concepts.
Thanks
First method:
#RequestMapping(method=RequestMethod.GET)
public String create(Model model){
model.addAttribute(new User());
return "index";
}
Second Method:
#Autowired
User user;
#RequestMapping(method=RequestMethod.GET)
public String create(Model model){
model.addAttribute(user);
return "index";
}
By using dependency injection does not mean that the use of new operator is automatically prohibited throughout your code. It's just different approaches applied to different requirements.
A web application in spring is composed of a number of collaborating beans that are instantiated by the framework and (unless overriding the default scope) are singletons. This means that they must not preserve any state since they are shared across all requests (threads). In other words if you autowire the User object (or any other model attribute), it is created on application context initialization and the same instance is given to any user request. This also means that if a request modifies the object, other requests will see the modification as well. Needless to say this is erroneous behavior in multithreaded applications because your User object (or other model attribute) belongs to the request, so it must have the very narrow scope of a method invocation, or session at most.
You can also have spring create beans with different scopes for you, but for a simple scenario of a model attribute initialization, the new operator is sufficient. See the following documentation if interested in bean scopes : Bean scopes
So in your use case, the second method is totally wrong.
But you can also delegate the creation of your model attributes to spring if they are used as command objects (i.e. if you want to bind request parameters to them). Just add it in the method signature (with or without the modelattribute annotation).
So you may also write the above code as
#RequestMapping(method=RequestMethod.GET)
public String create(#ModelAttribute User user){
return "index";
}
see also : Supported method argument types
If you want your beans to be "managed" by Spring (for e.g. to use with Dependency Injection or PropertySources or any other Spring-related functionality), then you do NOT create new objects on your own. You declare them (via XML or JavaConfig) and let Spring create and manage them.
If the beans don't need to be "managed" by Spring, you can create a new instance using new operator.
In your case, is this particular object - User - used anywhere else in code? Is it being injected into any other Spring bean? Or is any other Spring bean being injected in User? How about any other Spring-based functionality?
If the answer to all these questions is "No", then you can use the first method (create a new object and return it). As soon as the create() method execution is complete, the User object created there would go out of scope and will be marked for GC. The User object created in this method will eventually be GC-ed.
Things can be injected in two ways in a Spring MVC applications. And yes, you can you can mix injection and creation if doing right.
Components like the controller in your example are singletons managed by the application context. If you inject anything to them it is global, not per request or session! So a user is not the right thing to inject, a user directory can be. Be aware of this as you are writing a multithreaded application!
Request related things can be injected to the method like the used locale, the request, the user principal may be injected as parameters, see a full list at Spring MVC Documentation.
But if you create a model attribute you may use new() to create it from scratch. I will not be filled by spring but to be used by your view to display data created by the controller. When created in the request mapped method that is ok.
I am wondering what are the requirements for a method (or a class) to be labeled with #Controller? As for input arguments, the Spring tutorial seems to indicate that methods can sometimes take in nothing and sometimes take in a Model object:
http://blog.springsource.com/2011/01/04/green-beans-getting-started-with-spring-mvc/
And this:
Spring MVC Controllers Return Type
seems to indicate that the return type can be a String or a ModelAndView. I tried to look that up in the official documentation but couldn't find much info. I presume there must be some requirements. Any pointers?
In Spring Class is marked as #Controller, methods are marked as #RequestMapping handling specific request based on parameter,url path, accept header etc.
Spring MVC is highly flexible and allows you to have many return types see spring reference see "Supported method return types" section on the same page.
Also spring-mvc-3-showcase blog
I have been reading this forum for quite awhile and find it VERY useful, thank you to the contributors. I have a question that has plagded me for several weeks. And here it goes.
#RequestMapping(value="updateNote.htm",method=RequestMethod.POST)
public String updateNote(#ModelAttribute("note")NoteBean nb, BindingResult res,Model model){
daoobj.updateNote(nb.getName(),nb.getPath(), nb.getNote());
model.addAttribute("note",daoobj.getByName(nb.getName()));
return("success");
}
#RequestMapping(value="updateNote.htm",method=RequestMethod.GET)
public String updateNote(#ModelAttribute("note")NoteBean nb,Model model){
populateNoteBean();
model.addAttribute("note",daoobj.getByName(nb.getName()));
return("editNote");
}
#ModelAttribute("WHAT")
public NoteBean populateNoteBean() {
NoteBean nnb = new NoteBean();
return nnb;
}
With the method populateNoteBean() the model attribute is "WHAT". But, the name that I use is "note". So when I run the code, the NoteBean is correctly saved to the data base. My question is HOW?? It seems that the name "WHAT" should be "note" or that the model attribute is saving it as no name.
Thank for your time.
With your current code you will have two instances of your notebean in the model!
First spring invokes all modelattribute annotated methods in your controller and places the results in the model. Second it evaluates the ones from your requestmapping method.
The point of a modelattribute annotated method is that you can choose how to create your bean. Load it for example from a database.
We use this approach like that:
modelattr method (name="note")
Loads beans from db
requestmapping method with modelattr param (name="note")
Merges the note bean created by the first method with the request paramters from a submit for example and you habe directly access to the modifed one.
One nice effect:
We do not want to put hidden input fields for all attributes in a form just to be able to merge the entity with the entitymanager. This way you can have a form with only one attribute (plus one for the id to be able to fetch the entity)
Or another one:
If your note bean is an abstract class spring has no possibility to instanciate the bean because it does not know what to instanciate. You can for example add a requestparam parameter in the modelattr annotated method and decide what to do yourself.
This is very well described in the documentation. Either the reference or in the api of either controller, reqestmapping or modelattribute i believe.
With Spring, how can i retrieve the following Controller attributes in the view?
Controller name
Controller's #RequestMapping URI
Action method name
Action method's #RequestMapping URI
One approach which i have tried is by creating a subclass of HandlerInterceptorAdapter and overriding postHandle. I register my subclass as an mvc:interceptor for a list of given paths - which is clunky to maintain but was the only way to avoid my interceptor being called for ResourceHandler requests (which i don't want). In my postHandle i can easily add the 2 name attributes, but not the URIs...
Parsing from the HttpRequest object requires constraints on all Controller RequestMappings. I.e. i must always map /Controller/Action or equiv scheme. Quite limiting.
Creating an ApplicationContext and querying that with the requestURI is too long-winded.
I am thinking about dropping the HandlerInterceptorAdapter and instead defining a BaseController for all my controllers to extend.
I wanted to ask before i do this, is there a better approach?
You haven't stated why you need to do this (it sometimes helps to include your motivation, as others can suggest alternative approaches).
But I'm guessing that the Spring 3.1 features loosely termed "end point documentation" may do what you are asking... See RequestMappingHandlerMapping in the Spring documentation which doesn't provide a lot of detail, so this example project is the best place to see it in action:
Spring MVC 3.1 Demo App
example controller
example JSP page
I'd like to be able to create a base controller in my Spring app that, among other things, determines if a user is a registered user or not. This base controller, following the template design pattern, would contain an abstract protected method that controller subclasses would implement.
The abstract method would have passed to it an instance of User, registered or otherwise. However, I have no idea how I would do this since it seems that by using controllers purely using the #Controller annotation each controller is free to define their request handling method however they like.
Would creating some sort of user service class that is injected into each controller and used to validate a user be one way to get around this? This begs the question (at least for me) how does such a controller get a hold of a HttpServletRequest or the Session object?
Thanks.
Define an abstract BaseController, with no annotations
Define concrete and abstract methods
Call these methods from subclasses (which are annotated with #Controller) whenever needed.
I think the Base Controller is not a good idea if the only code it is to have is for UserAuthentication...instead use Spring security. This is the best option.
Alternatively, you can have methods like this...take a look at the Spring reference..
#Controller("loginController")
public class LoginController {
#RequestMapping(value="/login.do", method=RequestMethod.POST)
public String login(Model model, HttpServletRequest request) {
String userIdFromRequest = (String)request.getParameter("userId");
String password = (String)request.getParameter("password");
boolean verified = ...send userIdFromRequest and password to the user service for
verification...
if (verified){
request.getSession().setAttribute("userId", userIdFromRequest);
}
}
//More Methods
}
Did it help?
-SB
The basic problem is that annotational bootstrapping is not polymorphic. I found this paper useful: http://sanguinecomputing.com/design-pattern-for-hierarchical-controller-organization-with-annotational-configuration-spring-mvc-3/