Session-scoped RMI Proxy

[Roxton]

I want each session to use a different server for RMI calls. My reasons are a little unorthodox, but you can imagine the case of somebody wanting to do load-balancing (badly).

The following configuration shows my intent, but of course you can't scope an RmiProxyFactoryBean this way. Can anyone help me achieve what I want to do?

    <bean id="myService" class="org.springframework.remoting.rmi.RmiProxyFactoryBean" scope="session">
        <aop:scoped-proxy />
        <property name="serviceUrl">
            <bean class="com.company.MyServiceSessionURL" scope="session" />
        </property>
        <property name="serviceInterface" value="com.company.MyServiceInterface/>
        <property name="lookupStubOnStartup" value="false" />
        <property name="refreshStubOnConnectFailure" value="true" />
    </bean>

MyServiceSessionURL determines the appropriate server (and thus serviceUrl) for the session.

[Jörg Heinicke]

I wonder if it works to just make the serviceUrl a session-scoped bean proxy.

Joerg

[Roxton]

I'll try, but I don't think that will work. The documentation explicitly warns against hooking scoped beans into singletons without an <aop:scoped-proxy>, because otherwise the scoped bean is instantiated exactly once.

[Roxton]

I can't try it, because serviceUrl requires a String, and MyServiceSessionURL isn't a String. Is there a way to assign a conversion strategy that simply calls toString() on the MyServiceSessionURL object? Or a way to use a non-static field?

[Roxton]

Follow-up -- Success:
I was able to get a session-scoped RMI proxy with a little finagling.

    <bean id="myService" class="com.company.MyServiceDelegator" scope="session">
        <aop:scoped-proxy />
        <property name="remoteMyService">
            <bean class="org.springframework.remoting.rmi.RmiProxyFactoryBean">
                <property name="serviceUrl">
                   [...]*
                </property>
                <property name="serviceInterface" value="com.company.MyService"/>
                <property name="lookupStubOnStartup" value="false" />
                <property name="refreshStubOnConnectFailure" value="true" />
            </bean>
        </property>
    </bean>

public class MyServiceDelegator implements MyService {

    private MyService remoteMyService;

    public MyService getRemoteMyService() {
        return remoteMyService;
    }

    public void setRemoteMyService(final MyService remoteMyService) {
        this.remoteMyService= remoteMyService;
    }

    public void serviceCall(...) {
        remoteMyService.serviceCall(...);
    }
}

Now, I can transparently inject myService into any bean that needs to use the MyService interface.


* The [...] represents an unsolved problem. In actuality, I subclassed RmiProxyFactoryBean to override the setServiceUrl method, but that's pretty disgusting and shouldn't be necessary.

[Jörg Heinicke]

The documentation explicitly warns against hooking scoped beans into singletons without an <aop:scoped-proxy>, because otherwise the scoped bean is instantiated exactly once.

Yes, I wrote "session-scoped bean proxy".

Or a way to use a non-static field?

Yes, you can use a so-called instance factory method:

<bean id="myServiceSessionURL" class="com.company.MyServiceSessionURL"/>

<!-- injectable string -->
<bean id="sessionUrl" factory-bean="myServiceSessionURL"
                      factory-method="toString"/>

Both are also session-scopable.

Joerg

[Roxton]

Thanks a lot, Jörg. The factory-bean approach worked perfectly.

As for the other thing, it seems that the RmiProxyFactoryBean wouldn't know that the sessionUrl was a scoped proxy, and would call it exactly once to create a singleton. Scoped proxies are supposed to be transparent to the caller. The Delegator seems to do the trick, though.