유겐 휄러(Juergen Hoeller) 횽아한테 스프링 한 수 배우다.

We are using GenericController with Spring 2.5 @Controller APIs. And we are using @SessionAttribute like this.

@SessionAttributes(value="model")

This session attribute name "model" are used by many diffent controllers and many JSPs.

The problem is that diffent session attribute stored with same name(here is "model").

ex, When open pop-up page from parent page, the pop-up page's session
attribute will override the parent page's session attribute with same
name "model". So, after close the pop-up and if we click save button on
parent page, we can meet ClassCastException. ^^;;

We resolve this by modify org.springframework.web.bind.annotation.support.HandlerMethodInvoker class

updateModelAttributes method's

from

this.sessionAttributeStore.storeAttribute(webRequest, attrName, attrValue);

to

this.sessionAttributeStore.storeAttribute(webRequest, attrValue.getClass().getSimpleName() + attrName, attrValue);

and resolveModelAttribute method's

from

Object sessionAttr = this.sessionAttributeStore.retrieveAttribute(webRequest, attrName);

to

Object sessionAttr = this.sessionAttributeStore.retrieveAttribute(webRequest, paramType.getSimpleName() + attrName);

This modification don't need any change or modification existing
Controllers and JSPs. They now use there own session with same name.

How about apply this modification?

And could you remove final keywords from HandlerMethodInvoker to extend that class?

Now we just copy and paste original source and modify this above
code, and AnnotationMethodHandlerAdapter too.
AnnotationMethodHandlerAdapter class using inner class thar extends
HandlerMethodInvoker(ServletHandlerMethodInvoker). So we change the
HandlerMethodInvoker import statement in AnnotationMethodHandlerAdapter
to our modified version. kk.. Please think about it.

We actually envisioned such use cases and designed the
SessionAttributeStore strategy accordingly... You should be able to
implement your custom attribute prefix strategy through decorating the
SessionAttributeStore, configuring your custom decorator through the
"sessionAttributeStore" property on AnnotationMethodHandlerAdapter.

Juergen

I saw SessionAttributeStore class but in this case that class cann't help us.

Bacause, the session attribute's (internal) name sould be change
according to the command object's class's name(or each controllers).

Yes, we could do this by add @SessionAttribute(name="foobar") on
every controllers. but, we made and use custom tags that expects only
one session attribute name "model". So we set
@SessionAttribute(name="model") this on GenericController and we don't
set any @SessinoAttribute on sub-clsss of GenericController.(If you
want to see this class code, I can show you.)

With SessionAttributeStrore extending, we can only set a static
prefix(this is not what i want.). Even if we can modify storing name by
overriding storeAttribute(WebRequest request, String attributeName,
Object attributeValue) method with
attribute.getClass().getSimpleName()(ex. "Foomodel"), but how can we
pick up that session object by that name(ex. "Foomodel") by overring
retrieveAttribute(WebRequest request, String attributeName) method. We
can't. There is not enough information about runtime command object
type or name.

We want to use only one static session attribute name (not prefix)
that can be stored and can be retrived according to there runtime
object type.(ex. FooController(extends GenericController) reference Foo
command object in session by "model"(internally "Foomodel"). And
BarController(extends GenericController) also can reference Bar command
object in session by "model"(internally "Barmodel".)

So we just do that in here(above modified HandlerMethodInvoker class).

At least we want to extend HandlerMethodInvoker class and set to AnnotationMethodHandlerAdapter.

Is there another way to do this?

Good point - you can't include the param type name in the session attribute name that way.

However, I would argue that including the param type is a half-baked
solution to begin with: That way you'll isolate per param type, which
will work when different windows operate on model attributes of
different type. However, what if multiple windows operate on the same
type of attribute? What if the same controller gets opened multiple
times, e.g. to concurrently edit business accounts of different
customers in multiple windows?

The idea behing the SessionAttributeStore strategy is that it may
use a custom conversation mechanism: either storing attributes in a
managed conversation object instead of in the plain session, or
prefixing attribute names with a conversation identifier and still
storing them in the session directly. The latter is what I would
recommend for your purposes: Determine a conversation identifier for
each request (from the given WebRequest object, e.g. from the URL or
from a parameter) and use it as a prefix for each attribute name. This
will work for storage as well as for retrieval, and will even work for
multiple windows that operate on the same type of attribute.

Juergen

Thanks. I missed that situation (multiple windows on same type) and misunderstanded SessionAttributeStore.

I'll try to use SessionAttributeStore. I really appreciate your recommendation. ^^

Good!! We resolve this issue with you advice.

We made an interceptor that can capture URI, and made a custom
SesstionAttributeStore that make session attribute session attribute
using captured URI by WebRequest. Finally we configure it to
AnnotationMethodHandlerAdapter

Juergen Hoeller resolved SPR-4818.
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