How to inject a bean only when it exists

Question

I have the following structure of spring context files ( -> stands for \'includes\') :

A1.xml -> B.xml & C.xml
A2.xml -> B.xml


        

Answer 1

I quite agree with cleaning up your XML :-)

If you're using annotation based injection, you might try this trick

@Autowired( required=false )

I'm unsure whether this will work in your situation, but it's worth a try.

Answer 2

The #root object of the SpEL Expression is a BeanExpressionContext, you can invoke the getObject() method on that context; it returns null if the bean is not declared...

<property name="bar" value="#{getObject('bar')}" />

Note: you use value not ref because it returns the bean, not the bean definition.

Here's the code from getObject()

public Object getObject(String key) {
    if (this.beanFactory.containsBean(key)) {
        return this.beanFactory.getBean(key);
    }
    else if (this.scope != null){
        return this.scope.resolveContextualObject(key);
    }
    else {
        return null;
    }
}