Datasheet

the required resource and then injects it into the component, effectively inverting the control over the

selection of the resource from the component to the container.

Figure 1-3

Dependency Injection

Since the Spring code shown is dependent on the availability of the DataSource instance to work, and

the instance is injected into the component via the

setDs() method, this technique is often referred to as

dependency injection. In fact, the use of the setter method,

setDS(), to inject the DataSource code depend-

ency is known as setter injection. Spring also supports constructor injection, in which a dependent resource

is injected into a bean via its constructor.

Try It Out Creating a Dependency Injection

To see dependency injection in action, you do not even have to rebuild your project — since beans are

wired via the context descriptor in Spring.

1. Go back to the src/chapter1/springfirst directory and run CalculateSpring:

mvn exec:java -Dexec.mainClass=com.wrox.begspring.CalculateSpring –Dexec.args=”3000 3”

The current bean is autowired with an Operation implementation that adds two numbers

together. And you see the output:

The result of 3000 plus 3 is 3003!

2. Change the directory to edit the context descriptor in the src/chapter1/springfirst/

target/classes

directory:

cd src/chatper1/springfirst/target/classes

CalculateSpring (component)

2. Injects ScreenWriter

for writer property

Container

IoC Container

OpMultiply ScreenWriter

1. Give me OpMultiply

2. Here is OpMultiply

3. Give me ScreenWriter

4. Here is ScreenWriter

Calculate (component)

ops property

writer property

1. Injects OpMultiply

for ops property

OpMultiply

ScreenWriter

Chapter 1: Jump Start Spring 2

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