Apply dynamic properties to a bean at runtime

Question

Assume I have a bean DialogBox, with properties for height and width:

public class DialogBox {
 int x;
 int y;
 ...
}

In my applicationContext.xml I would define properties as reasonable defaults:

<bean id="dialogbox" class="DialogBox">
  <property name="x" value="100"/>
  <property name="y" value="100"/>
</bean>

We have multiple clients that use the dialogBox bean, and each wants a custom value for x and y. One route we have discusses is having multiple properties files, one for each client, and have the client id map to the proper file, for example client 123 would map to dialogbox_123.properties:

dialogbox_123.properties:
x=200
y=400

Then at runtime when the bean is requested, spring would look to see if a custom properties file exists for the client, and use those properties, otherwise use the defaults. I am aware of the PropertyOverrideConfigurer, but AFAIK this only works when the context is started so will not work for our purposes. Is there an existing facility in spring to achieve this, or can someone recommend another way?

Answer 1

If I understood the question, you can use a FactoryBean to customize bean creation logic in Spring.

Answer 2

1. Use FactoryBean (as already suggested) to customize instantiation.
2. set scope="prototype" on the bean, so that each time an instance is required, a new one should be created.
3. In case you want to inject the prototype bean into a singleton bean, use lookup-method (Search for lookup-method here)

I'm not sure if this would fit your case though. Another suggestion would be:

In @PostConstruct methods of your various "clients" set the properties as desired on the already injected dialog window. Like:

public class MyDialogClient {
    @Autowired
    private Dialog dialog;

    @PostConstruct
    public void init() {
        dialog.setWidth(150); //or read from properties file
        dialog.setHeight(200);
    }
    ...
}

Again, in this case, you can play with the scope atrribute.

Answer 3

Take a look at the Spring OSGi Compendium services, they've got a property manager called "managed-properties", which allows you not only to update the properties at runtime, but while the application is running if you select the "container-managed" update strategy.