Hi!
I have a question about concurrency in a web application I hope someone could resolve for me.
I have an application with a session destroyed listener X. Inside this listener there is an autowired singleton Y which also has another bean autowired inside it Z.
My question is; if I have Z defined with request scope, when I make a call from X to Y, will it have a new instance of Z with each call or it will just have the same instance again and again?
Thanks in advance!
To inject a request scoped bean into a singleton you should inject an aop scoped proxy, see
http://static.springsource.org/sprin...ther-injection
Thank you!
That's exactly what I needed
Another question related to this.
Suppose this prototype bean is only used inside a method. What do you recommend?
- Get the application context and obtained an instance of the prototype bean inside this method so there is no need for an instance variable
- Create an aop scoped proxy as an instance variable to retrieve a real instance of the object with each call
I don't know about perfomance. For me it seems easier and cleaner to just create the instance variable with autowire and use it as if it was a regular singleton but I guess it's more efficient the other way
Creating scoped proxies for prototypes is not a good idea, you will get a new instance on every method call. For example:
As getName() is executed on a new instance...Code:prototypeScopedProxyInstance.setName("Peter");
boolean willBeFalse = "Peter".equals(prototypeScopedProxy.getName());
You can use ApplicationContext to get the prototype or use Lookup Method injection, if you want to keep decoupled your class from spring library.
Ok, I've tried with lookup method injection and it works well. I had to rewrite the class to make it abstract and create the abstract method to get it overriden by spring. I tried creating a new method without changing the class to abstract but it doesn't work. For what I read in the documentation, if the class is not abstract, spring overrides the method you define in the lookup-method tag. If I don't change the class to abstract and also define the method abstract, when I call the method in my application, it uses the one defined in the class, no the one defined in the xml.
Is it normal or did I do something wrong? Also, if I keep this class abstract but I create some other abstract methods I don't define inside a lookup-method tag, what does spring do with them? Does it create stub implementations of these abstract methods, returning null if the functions have to return some value?
No lookup or replaced methods are delegated to super implementation so them can not be abstract. A java.lang.AbstractMethodError will be throw when calling thems on the generated proxy
The class don't need to be abstract for a lookup method, ensure that you are calling to a cglib proxy injected by container in your application and no to a instance created with new operator.
My class definition is something like this
<bean id="prototypeClass" class="package.PrototypeClass" scope="prototype" />
<bean id="singletonClass" class="package.SingletonClass">
<lookup-method bean="prototypeClass" name="getPrototypeClass"/>
</bean>
And the method definition is like this
If I don't change SingletonClass and getPrototypeClass method to abstract, when I call getPrototypeClass() I get a null pointer. Do I have to put something special inside getPrototypeClass method? If I don't define the class abstract I need to implement this method and it doesn't seem too clean just leaving it with a null returned value.Quote:
//Singleton class
public class SingletonClass {
....
private void someMethod(){
....
PrototypeClass prototype = getPrototypeClass();
...
}
private PrototypeClass getPrototypeClass(){
return null;
}
}
Make getPrototypeClass() public or protected to let container override it.