Spring bean scope based on dynamic constructor value

Question

I have to create a bean where it needs to be cached based on the dynamic constructor value. Example: I need an OrganizationResource bean where "x" (constructor value) organization will have its own specific instance values and "y" (constructor value) will have different values. But I don't want to create a new object for every x value, I want it to be cached.

I know there are 2 scopes, singleton and prototype, for dynamic constructor value. I am planning to use prototype, but it seems it will create a new object every time, how can I implement cache based on constructor value in spring?

Sounds to me like you should consider a Factory pattern here? — Anders R. Bystrup
– Anders R. Bystrup, Commented Nov 5, 2012 at 12:13
Thanks for the response, does spring not provide any other way? — Ramesh V
– Ramesh V, Commented Nov 5, 2012 at 12:25
1.I don't think that creating an extra object will have any noticable impact on the performance - GC is pretty much optimized for collecting young objects. 2. I'm not sure that IoC container is a good place to create business objects - especially entities, which are likely to be better managed with a JPA compatible framework . — Boris Treukhov
– Boris Treukhov, Commented Nov 5, 2012 at 13:20
You might be able to do this with a custom scope. You do NOT have to use scopes that Spring provides... — nicholas.hauschild
– nicholas.hauschild, Commented Nov 5, 2012 at 14:27
@nicholas I'm not sure that it's prohibited to specify a factory-method for the prototype scoped beans that will either return a reference to the existing object or will return a new object - depending on the environment state or the argument values. — Boris Treukhov
– Boris Treukhov, Commented Nov 5, 2012 at 17:44

Marcin · Accepted Answer · 2013-02-01 12:28:49Z

FactoryBean is a way to go. It is very simple, give it a try. All you have to do is create a class implementing FactoryBean and reference it in bean definition file:

package some.package;
import org.springframework.beans.factory.FactoryBean;

public class ExampleFactory implements FactoryBean {

private String type;

public Object getObject() throws Exception {
    //Logic to return beans based on 'type'
}

public Class getObjectType() {
    return YourBaseType.class;
}

public boolean isSingleton() {
    //set false to make sure Spring will not cache instances for you.
    return false;
}

public void setType(final String type) {
    this.type = type;
}}

Now, in your bean definition file, put:

<bean id="cached1" class="some.package.ExampleFactory">
    <property name="type" value="X" />
</bean>

<bean id="cached2" class="some.package.ExampleFactory">
    <property name="type" value="Y" />
</bean>

It will make objects based on strategy you implemented in ExampleFactory.getObject().

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