EduSpring Part 1: Introduction

Monday, June 13, 2011

I get quite a few questions about Spring.Net, so I thought I'd put together a VS Solution, presentation, and set of blog posts to provide some background and details about what it is, why/when to consider using it, and how to configure and debug the framework.

A lot of this material will not be specific to Spring.Net, but rather Dependency Injection generally.  To understand Spring.Net, you must be familiar with Inversion of Control and Dependency Injection.  You can read about them on Wikipedia, but here's a short summary:

Inversion of Control: Flow of control of a system is inverted in comparison to procedural programming
Dependency Injection: A specific technique to achieve inversion of control with respect to dependencies

What this means in layman's terms is that instead of a program:

  1. Starts up
  2. Creating new services for whatever needs to be done
  3. Using the services/doing the work
  4. Disposing of the services and returning the results
The program now does only what it's responsible.  Namely:
  1. Starts up
  2. Uses services that have been configured for its use/does the work
  3. Returns the results
This makes the program itself easier to test, simpler to code/maintain, and separates infrastructural responsibilities (determine location of services and creating them) from the business logic the program was created to deliver.

The devil in these particular details are in #2.  How does one create and configure services for a program?  We can code this by hand, but it's a lot of boring glue code, and doing it right is incredibly difficult.  Enter the IoC container - a piece of pre-built code that will do this work for us.  Depending on the application, we don't even need to use the container explicitly.  In a system like ASP.NET, we can use HttpModules to intercept requests and wire dependencies automatically.

One significant problem with this approach are the complexity of configuration.  Using, I can have a dependency-injected factory method to deliver an instance of an object used to populate a property that will be injected into another object that will have additional advice applied through Spring.Net's AOP module.  When that fails, I might get a "node cannot be resolved for the specified context" without any additional information pointing me to the cause of the problem.  With flexibility comes complexity.

Another issue is a fundamental problem with .NET (C# and VB and I believe all .NET classes adhering to the CLI).  Interfaces are incomplete contracts.  

Finally, with regards to Spring.Net in particular, the framework can be slow to move (IIS7 Integrated mode, introduced with Windows Server 2008 on Feb 27, 2008, gained support in Spring.Net 1.3.1 released December 10, 2010).  Also, no Mono support exists as of this writing.

Next up - some walkthrough code.

Emil's Wicked Cool Blog