Inversion of Control (IOC)/ Dependency Injection (DI) / Spring
The basic concept of the Inversion of Control pattern (dependency injection) is that programmers don’t need to create your objects but describe how they should be created. Don’t directly connect components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the Spring framework, the IOC container) is responsible for all this. In a IOC scenario, the container creates all the objects, connects them together by setting the necessary properties, and determines when methods will be invoked. The implementation pattern types for IOC used by SpringFramework are as follows:
Ø Dependencies can be assigned through JavaBeans properties (setter methods).
Ø Dependencies are provided as constructor parameters and are not exposed as JavaBeans Setter propertiSes.
Spring IOC Container
Big advantages I have seen with inversion of control, that we don’t directly connect with services but we configure that. Now this is really gaining momentum as of late, is the adoption of the Spring Framework as an alternative to Java EE. I think that this started because J2EE was so complicated and heavy-weighted that companies sought new and innovative solutions. Spring provides the ability to access data objects as Plain Old Java Objects (POJOs) and includes support for database connection pools, transaction management, and so forth. This means that you can effectively build a scalable enterprise application without Java EE. And as Java EE evolved into its more manageable form, many developers continued to appreciate all that Spring provided them and had no desire to switch back.
As an enterprise developer you should be familiar with the concept of Inversion of Control (IoC) and Dependency Injection, and Spring specifically. Whether you decide to embrace Java EE and EJB 3.0 or develop your applications with Spring, you should at least understand the theory.
Book Recommendations:
· Spring in Action by Craig Walls, Ryan Breidenbach: this is the best book I have read on Spring (and yes I read this entire book).