Scope of a Spring-Controller and its instance-variables - Spring - Java

yes, Spring MVC controllers are singletons by default. An object field will be shared and visible for all requests and all sessions forever.
However without any synchronization you might run into all sorts of concurrency issues (race conditions, visibility). Thus your field should have volatile (and private, by the way) modifier to avoid visibility issues.
Back to your main question: in Spring you can use request- (see 4.5.4.2 Request scope) andsession-scoped (see: 4.5.4.3 Session scope) beans. You can inject them to controllers and any other beans (even singletons!), but Spring makes sure each request/session has an independent instance.
Only thing to remember when injecting request- and session-scoped beans into singletons is to wrap them in scoped proxy (example taken from 4.5.4.5 Scoped beans as dependencies):
<!-- an HTTP Session-scoped bean exposed as a proxy -->
<bean id="userPreferences" class="com.foo.UserPreferences" scope="session">

    <!-- instructs the container to proxy the surrounding bean -->
    <aop:scoped-proxy/>
</bean>

Comments

Post a Comment

Popular posts from this blog

public vs protected vs default access modifiers - Java

| Class | Package | Subclass | Subclass | World | | |(same pkg)|(diff pkg)| ————————————+———————+—————————+——————————+——————————+———————— public | + | + | + | + | + ————————————+———————+—————————+——————————+——————————+———————— protected | + | + | + | + | ————————————+———————+—————————+——————————+——————————+———————— no modifier | + | + | + | | ————————————+———————+—————————+——————————+——————————+———————— private | + | | | | + : accessible blank : not accessible
Read more

Class, Reference and Object

If you like housing metaphors a  class  is like the blueprint for a house. Using this blueprint, you can build as many houses as you like. each house you build (or instantiate, in OO lingo) is an  object , also known as an  instance . each house also has an address, of course. If you want to tell someone where the house is, you give them a card with the address written on it. That card is the object's  reference . If you want to visit the house, you look at the address written on the card. This is called  dereferencing . You can copy that reference as much as you like, but there's just one house -- you're just copying the card that has the address on it, not the house itself. Java methods are always pass-by-value, but the value could be an object's reference. So, if I have: Foo myFoo = new Foo (); // 1 callBar ( myFoo ); // 2 myFoo . doSomething () // 4 void callBar ( Foo foo ) { foo = new Foo (); ...
Read more