CODEWITHSUNDEEP
spring
Beginner
Beginner

Reputation: 225

Injecting dependencies

The basic principle behind Dependency Injection (DI) is that objects define their dependencies (that is to say the other objects they work with) only through constructor arguments, arguments to a factory method, or properties which are set on the object instance after it has been constructed or returned from a factory method.

Here what exactly is this factory method?

Upvotes: 0

Views: 203

Answers (2)

Andrei Stefan
Andrei Stefan

Reputation: 52368

Take a look at the last example in this Spring reference documentation section.

This is the sample:

<bean id="exampleBean" class="examples.ExampleBean" factory-method="createInstance">
    <constructor-arg ref="anotherExampleBean"/>
    <constructor-arg ref="yetAnotherBean"/>
    <constructor-arg value="1"/>
</bean>

<bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>

ExampleBean class:

public class ExampleBean {

// a private constructor
private ExampleBean(...) {
    ...
}

// a static factory method; the arguments to this method can be
// considered the dependencies of the bean that is returned,
// regardless of how those arguments are actually used.
public static ExampleBean createInstance (
    AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) {

    ExampleBean eb = new ExampleBean (...);
    // some other operations...
    return eb;
}

}

So, an instance of a bean is created using a factory-method inside the same bean. And the dependency injection is achieved by passing other beans as arguments to the factory-method.

Upvotes: 1

Maxim Kirilov
Maxim Kirilov

Reputation: 2739

Factory Method is a design pattern for object creation. The Factory Method defines an interface for creating objects, but lets subclasses decide which classes to instantiate. For more information you can read here.

Upvotes: 0

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