Optional Spring bean references

Question

In my application I am using ContextLoaderListener to load context files from many jars using:

    contextConfigLocat         


        

Answer 1

what method do you recommend for handling dynamic references?

I think @cristian's @Autowired answer is a good one. That will call the setter methods if the beans of that type are available. However, if you have multiple beans of the same type, I believe Spring throws an exception. If you cannot use @Autowired for this or some other reason, I see a couple of solutions:

1. You could make your class ApplicationContextAware and lookup the beans in the context yourself:

   public void setApplicationContext(ApplicationContext applicationContext) {
       if (applicationContext.containsBean("optionalBeanReference1")) {
           setOptionalBeanReference1(
               (OptionalBeanReference1)applicationContext.bean(
                   "optionalBeanReference1");
       }
       ...
   }
   

2. You could invert the dependency. Each of the optional classes could set themselves on the mainAppBean. I use this in certain situations when a direct dependency would cause loops or other problems.

   Then in the SomeClass:

   public SomeClass(com.someapp.MyApplication mainAppBean) {
       mainAppBean.setOptionalBeanReference1(this);
   }
   

3. You could stay with your direct dependency and then either import a file with the beans defined or import another file where you define the beans as having null values by using a factory bean. See this factory code.

Good luck.