Let’s face it, there are two kinds of developers: those that favor Spring autowiring because it alleviates them from writing XML (even though you can do autowiring with XML) and those that see autowiring as something risky.
I must admit I’m of the second brand. In fact, I’d rather face a rabbied 800-pounds gorilla than use autowiring. Sure, it does all the job for you, doesn’t it? Maybe, but it’s a helluva job and I’d rather dirty my hands than let some cheap bot do it for me. The root of the problem lies in the implicit-ness of autowiring. You declare two beans, say one needs a kind of the other and off we go.
It seems simple on the paper and it is if we let it at that. Now, autowiring comes into two major flavors:
- By name where matching is done between the property’s name and the bean’s name
- By type where matching is done between the property’s type and the bean’s type
The former, although relatively benign, can lead to naming nightmares where developers are to tweak names to make them autowire together. The second is an utter non-sense: in this case, you can create problems in a working context by creating a bean in it, only because it has the same class as another bean already existing in the context. Worse, autowiring errors can occur in a completely unrelated location, just because of the magic involved by autowiring. And no, solutions don’t come from mixing autowiring and explicit wiring, mixing autowiring between name and type or even excluding beans from being candidates for autowiring; that just worsens the complexity as developers have to constantly question what will be the behavior.
Autowiring fans that are not convinced should read the Spring documentation itself for a list of limitations and disadvantages. This is not to say that autowiring in itself is bad, just that is has to be kept strictly in check. So far, I’ve allowed it only for small teams and only for tests (i.e. code that doesn’t ship to production).
All in all, Spring autowiring has one redeeming quality: candidates are only chosen from the context, meaning instances outside the context cannot wreak havoc our nicely crafted application.
CDI developers should have an hint where I’m heading. Since in CDI every class on the classpath is candidate for autowiring, this means that adding a new JAR on the application’s classpath can disrupt CDI and prevent the application from launching. In this light, only autowiring by name should be used for CDI… and then, only by those courageous to take the risk