I.e. I only want a nice way to retrieve existing objects from my Model (mostly some SessionAttributes).
I don't want new objects to be created and I especially don't want objects to be instantiated from request parameters and put into the model. This just sounds like a back door to me.
It would also be great if an Exception can be thrown if no matching parameter is in the model.
I got the answer to this by reading the source code. According to the implementation of org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveModelAttribute, a new bind Object will not be created if the name of the model attribute is declared as a session attribute using the #SessionAttributes annotation.
If the attribute is not present in the session, an Exception will be thrown.
So it is relatively safe to bind session attributes this way.
Related
I'm using the #Scope annotation with value of "request".
How do I check if the given object with the "Scope" annotation is instantiated on each http request ?
Do the object (bean) have some identifier (hashcode ) ? And, I don't mean the bean id.
System.identityHashCode(theBeanVariable)
Print the hashes and check the objects are the same or not.
You gotta believe!
No, I'm kidding. Methods I used so far:
In eclipse if you stop application on a breakpoint you can check the id of every object in Variables tab. Every new instance of object has new id. You probably can find a place in your code that is executed after every (or some) request.
If you can set some fields of this bean via a web page, go and do it and then open the same page in new tab in your web browser. If request scope is working, fields you set should have old values (the one that are set on creation of object).
Maybe these are not uber-pro methods, but may be enough in some cases and you don't have to add anything in your code.
What is the best way to use SessionAttributes and ModelAttributes together? When I use, for example, a tagged ModelAttribute method and the SessionAttribute on the class, then the POJO is added to session, but in other controller that uses the same name for this kind of ModelAttribute then it does not retrieve the one I want but takes the one present in the session.
Then, what is the best way to manage the behaviour of ModelAttributes with SessionAttributes?
Thanks.
When you have done with the model in the session (I assume you just want to use that 'model in session' in specific Controller only) you have to set mySessionStat.setComplete() where in the parameter you declare SessionStatus mySessionStat
see:
SessionStatus api docs
Is it possible to give Spring MVC's form binding some kind of type hint to indicate what class to instantiate and populate with form data?
I've got some quite unusual requirements to try and build a dynamic form, that represents a collection of different objects. The user can add objects from a selection of types to this collection, and then set the properties for that object type using form elements. I can figure out how to create the form using jQuery, but I'm not sure how to get Spring to handle a load of POST data when it won't know what types to bind to in advance.
One way that I can think of doing this is to write your own custom HandlerMethodArgumentResolver , which is responsible for translating the request into the argument values of the controller methods. You should be able to create a custom annotation that will indicate to Spring MVC, that your custom handler method argument resolver will be resolving the specific annotated method arguments(say #CustomType Object argument).
Once the call comes into the handler resolver, you can probably determine the type that the json request should map to, and call the json mapper with the actual type.
You can register a custom argument resolver this way:
<annotation-driven>
<argument-resolvers>
<beans:bean class="..CustomArgumentResolver"/>
</argument-resolvers>
</annotation-driven>
I am trying to share data between two controllers in a Spring mvc application.
In Controller A I have annotated the class with #SessionAttributes({"mymodel1"}) and in the method which receives the first GET request I add it to the ModelMap:
model.addAttribute("mymodel1", MyModel1);
I now want to read myModel1 from Controller B.
In this Controller I have the following method which intercepts the POST requests and already has a different model in its parameters:
public String processSubmit(#ModelAttribute("mymodel2") MyModel2 mymodel2, BindingResult result, SessionStatus status, HttpServletRequest httpRequest)
Up to this point everything works fine and I am able to read mymodel2 from processSubmit however if I now want to add another #ModelAttribute("mymodel1") MyModel1 mymodel1 to this method signature I would have expected to be able to read the value I was setting in Controller A however I'm getting exceptions that the first model is no longer recognised.
So my question is: how can I read mymodel2 from Controller B?
You can't do that with #SessionAttributes :
Session attributes as indicated using this annotation correspond to a specific handlers model attributes, getting transparently stored in a conversational session. Those attributes will be removed once the handler indicates completion of its conversational session. Therefore, use this facility for such conversational attributes which are supposed to be stored in the session temporarily during the course of a specific handlers conversation.
For example I use this annotation when I want to validate elements with Hibernate validation, and after I submit the page and SOME elements are invalid I want the rest to be still on the page, but this is not your case. I think that the only way to do it would be with:
HttpSession.getAttribute()
The javadoc excerpt above is the most typical way #SessionAttributes is used. However, what Joly is describing should also work. Session attributes are stored via DefaultSessionAttributeStore, which by default does not prefix attribute names when it stores them in the session. That means if ControllerA and ControllerB both list an attribute called "mymodel1", they're actually referring to the same session attribute. You'll need to provide a little more information on the error you're getting and the actual controller code.
greetings all
i have a domain class named car
and i have an object from car retrieved from the DB
and i want to save this object in the form as a hidden field
in order when submitting to get this object
but when i tried
<form:hidden path=carObj />
it didn't work, any ideas why, and how to do such behaviour ?
Well carObj is a java object, and an HTML hidden field can only hold text, so how would Spring store one inside the other? If you want to use hidden fields, you're going to have to break down the object into individual fields.
It sounds like what you need is to tell Spring to store carObj in the session, so that's visible when the form is posted. You can use the #SessionAttributes annotation for this (see docs).
Spring's form tag library does indeed support hidden fields as you described.
See the Spring Reference for more information.