Question

I believe that most IoC containers allow you to wire dependencies with XML configuration file. What are cons and pros for using configuration file vs. registering dependencies in code?

Answer 1

These pros and cons are based on my work with spring. It may be slightly different for other containers.

XML

pro

• flexible
• more powerful than annotations in some areas
• very explicit modelling of the dependencies of your classes

con

• verbose
• difficulties with refactoring
• switching between several files

Annotations

pro

• less file switching
• auto configuration for simple wirings
• less verbose than xml

con

• more deployment specific data in your code (usually you can override this with xml configs)
• xml is almopst(?) always needed, at least to set up the annonation based config
• annotation magic may lead to confusion when searching for the class that is used as dependency

Code

pro

• Can take advantage of strongly-typed languages (e.g. C#, Java)
• Some compile-time checking (can’t statically check dependencies, though)
• Can take advantage of DSLs (e.g. Binsor, Fluent interfaces)
• Less verbose than XML (e.g. you don’t need to always specify the whole assembly qualified name (when talking .net))

con

• wiring via code may lead to complex wirings
• hard dependencies to IOC container in the codebase

I am using a mix of XML+Annotation. Some things especially regarding database access are always configured via xml, while things like the controllers or services are mostly configured via annotations in the code.

[EDIT: I have borrowed Mauschs code PROs]