Spring RegisterSingleton

Question

I have a following object:

public class TestObject
{
    public String Something { get; set; }
}

and a following objects file:

<?xml version="1.0" encoding="utf-8" ?>
<objects xmlns="http://www.springframework.net"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.springframework.net http://www.springframework.net/xsd/spring-objects.xsd"&gt;

  <object id="TestObject" type="SpringTest.TestObject" autowire="byName"/>
</objects>

What I would like to do is to register singleton and get the TestObject. I am doing this like so:

IConfigurableApplicationContext context = new XmlApplicationContext("objects.xml");
context.ObjectFactory.RegisterSingleton("Something", "something to test");
object obj = context.GetObject("TestObject");

But the objects property Something is always null. I think that this should work or am I doing something wrong?

Many thanks!

Answer 1

Why aren't you using scope="singleton" if you want a singleton or am I missing something?

Answer 2

I think your Something property is not getting set because singletons are instantiated when the application context is instantiated. When you call RegisterSingleton, the TestObject has already been created. The bean wiring is only done when a bean is created.

You might be able to work around this problem by making the singleton instantiate lazily. That way it isn't instantiated until the first time it's requested. Hopefully, that's after you've registered the other singletons it needs.

I don't know exactly what you're trying to accomplish, but if I wanted to change the wiring between some singleton beans at run time without making the beans aware of it, I would introduce some wrapper objects. Each wrapper would implement an interface and then just delegate all methods to its current target bean. To change the wiring, you just change the wrapper's target.

Update: as yawn suggested, Spring.NET has hot-swappable target sources that let you swap out the implementation of a bean at run time. Here's some sample code from the documentation that shows how to swap the bean implementation:

HotSwappableTargetSource swapper = 
    (HotSwappableTargetSource) objectFactory.GetObject("swapper");
object oldTarget = swapper.swap(newTarget);

The XML definitions in the documentation look like this:

<object id="initialTarget" type="MyCompany.OldTarget, MyCompany">
</object>

<object id="swapper" 
    type="Spring.Aop.Target.HotSwappableTargetSource, Spring.Aop">
    <constructor-arg><ref local="initialTarget"/></constructor-arg>
</object>

<object id="swappable" 
    type="Spring.Aop.Framework.ProxyFactoryObject, Spring.Aop">
    <property name="targetSource">
        <ref local="swapper"/>
    </property>
</object>

Answer 3

I'm not sure what the problem statement is exactly (never used Spring for .NET). But if you want what Don Kirkby suggest you should lookup TargetSources in the reference documentation (assuming that the .NET implementation has them, too).