Jsf / Spring 请求作用域bean

Question

As I don't have much experience in javaee programming and hasve noone to ask, i would like ask you. I have one thing in my code that i don't like and think it's implemented in wrong way. My managed bean are request scoped. in jsf i use rich:pickList which takes data from list.

@Scope("request")
public class MyBean{
     private List<String> sourceList;
     ....     

     public List<String> getsourceList() {
            //if (sourceList == null)    <--- Has no sence in request scoped bean
             { sourceList = service.loadList();
             }
             return sourceList;
     }

....

}

I have also submit button which store some data.

The problem is, that each time when the page do some actions (eg clicking submit button) this get method is invoked every time and goes to service layer, then to dao and to database. It obviously seems to be not correct solution. How to avoid it? Thanks' for you answers.

Answer 1

Everyone has this problem because there is no "conversation" scope. You have "session" (as long as the user is logged in) and "request" (one request/response cycle).

What you'd need is a way to say "user has started a conversation", then do a couple of requests that belong to the conversation and finally wrap it up.

Since this isn't supported by JavaEE, you have to emulate it. When the user starts the conversation, put the bean in the session scope and keep it there. When the user finishes the conversation, delete the bean manually or tell it to clean it's caches.

Answer 2

There is actually a "conversation scope" in Spring WebFlow:

http://static.springsource.org/spring-webflow/docs/2.0.x/reference/html/ch12s06.html

Answer 3

If you're on JSF 2.0, you can use the new view scope by @ViewScoped .

@ManagedBean
@ViewScoped
public class Bean {

    private List<Foo> foos;

    @EJB
    private FooService fooService;

    @PostConstruct
    public void init() {
        foos = fooService.list();
    }

    public List<Foo> getFoos() {
        return foos;
    }

}

When you're still on JSF 1.x, it's good to know that the RichFaces' <a4j:keepAlive> and Tomahawk's <t:saveState> have exactly the same effect on a request scoped bean with the above code design (ie do NOT load data in the getter):

<a4j:keepAlive beanName="#{bean}" />

and

<t:saveState beanName="#{bean}" />

I haven't used the new RichFaces' @KeepAlive annotation, but concerning the docs, it should behave the same as well.

Answer 4

Add the Spring RequestContextListener in web.xml that Spring can add the request scope and session scope.

<listener>
     <listener-class>
          org.springframework.web.context.request.RequestContextListener
     </listener-class>  
</listener>

Cf: 3.4.4. The other scopes