Update field annotated with @Value in runtime

问题:

Let's imagine we have such a component in Spring:

@Component
public class MyComponent {

    @Value("${someProperty}")
    private String text;
}

If we define the property placeholder:

<context:property-placeholder location="classpath:myProps.properties"/>  

And myPropos.properties contains the value for someProperty the value will be injected to the text field when the context is initialized. That's quite simple and easy.

But let's say that I have a service that enables user to change the value of the someProperty:

public void changeProp(String name, String newValue);

Is there a chance I can re-inject the newValue to text field. I mean it should be quite straight forward.. Basically it's nothing different than the after-initialization injection. I can not imagine that Spring does not have support for this? Can I fire some event or something?

I could do this on my own basically, but I wander is it maybe something there already? If not does anyone know what Spring class is in fact handling the injections at the first place? I could probably reuse the code there do perform this on my own if a solution does not exists.

回答1:

I expect spring does not have a support for this, because the normal injection is done while creating the bean, but not will it is put in service.

Anyway: in this blog entry "Reloadable Application Properties with Spring 3.1, Java 7 and Google Guava", you can find the idea for an solution.

The key idea is to use a post processor to build a list of all fields with property fields. And if the properties are changed on can use this list to update the fields.