Tuesday, March 22, 2016

Spring Annotations: Using Constructor Arugments with @Autowired


I've struggled for weeks with wanting to use a constructor with arguments along with Spring Annotations (in particular @Autowired) but most blog posts and tutorials say that this isn't possible or needs to use Spring Expressions.


There has got to be some way to do this.  The alternative I have been using was to have an empty object autowired in and then manually run a bunch of setters to inject the required configuration.  This ends up being error prone and verbose to verify (e.g. every public method has to check that the required fields are not null).


After searching the web for a long time I finally found that you CAN use multi-argument constructors if you refrain from using the @Component or @Service annotations and instead create the classes in a @Configuration class with @Bean annotations.  After creating a class (manually, with new) you can autowire it by using AutowireCapableBeanFactory.autowireBean(Object) method.


My code is a lot more readable and simple now, and let me find a few subtle bugs that did not turn up in the unit tests.  I ended up with complex object creation logic, but it is out in the @Configuration classes instead of inside of the core objects.  I am much happier with this situation.

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