How to inject a bean only when it exists

java, option-type, spring, spring-el

Solution

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;
    }
}

Problem

I have the following structure of spring context files ( `->` stands for 'includes') : ``` A1.xml -> B.xml & C.xml A2.xml -> B.xml ``` `C.xml` defines a bean `c` `B.xml` defines a bean `b` with a dependency on `c` Obviously this fails for A2, because there is no `c` defined in the context `A2`. How can I specify something like: if you have `c` in the context inject it in `b` otherwise just inject `null`? I looked into Spring EL but ``` <property name="b" ref="#{ @c?:null}" /> ``` Just gave me a `NoSuchBeanDefinitionException` for a name which seemed to be the value of `b.toString()` !? Btw: I already know that this thing is messy as hell and should be cleaned up as fast as possible.

Original source