Object-Oriented Techniques - Java - page 321

See Also

The javadoc documentation for Exception lists a large number of subclasses; you might
look there first to see if there is one you can use.

Using Dependency Injection

Problem

You want to avoid excessive coupling between classes, and you want to avoid excessive code
dedicated to object creation/lookup.

Solution

Use a Dependency Injection Framework.

Discussion

A Dependency Injection Framework allows you to have objects “passed in” to your code in-
stead of making you either create them explicitly (which ties your code to the implementing
class name, since you're calling the constructor) or looking for them (which requires use of a
possibly cumbersome lookup API, such as JNDI, the Java Naming and Directory Interface).

Three of the best-known Dependency Injection Frameworks are the Spring Framework , the
Java Enterprise Edition's Context and Depency Injection (CDI) , and Google Guice . Suppose
we have three classes, a Model, a View, and a Controller, implementing the traditional MVC
pattern. Given that we may want to have different versions of some of these, especially the
View, we'll define Java interfaces for simple versions of the Model and View, shown in the
following code:

Example 8-7. MVC Model Interface
public

public interface interface Model Model {

String getMessage ();

}

MVC View Interface