Rasimsen: Created page with "In the case of constructor-based dependency injection, the container will invoke a constructor with arguments each representing a dependency we want to set. Spring resolves e..."

2018-06-03T11:26:26Z

Created page with "In the case of constructor-based dependency injection, the container will invoke a constructor with arguments each representing a dependency we want to set. Spring resolves e..."

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In the case of constructor-based dependency injection, the container will invoke a constructor with arguments each representing a dependency we want to set.

Spring resolves each argument primarily by type, followed by name of the attribute and index for disambiguation. Let’s see the configuration of a bean and its dependencies using annotations:

<source>

@Configuration
public class AppConfig {

@Bean
public Item item1() {
return new ItemImpl1();
}

@Bean
public Store store() {
return new Store(item1());
}
}

</source>

The [[@Configuration]] annotation indicates that the class is a source of bean definitions. Also, we can add it to multiple configuration classes.

The [[@Bean]] annotation is used on a method to define a bean. If we don’t specify a custom name, the bean name will default to the method name.

For a bean with the default singleton scope, Spring first checks if a cached instance of the bean already exists and only creates a new one if it doesn’t. If we’re using the prototype scope, the container returns a new bean instance for each method call.

Another way to create the configuration of the beans is through XML configuration:

<source>
<bean id="item1" class="org.baeldung.store.ItemImpl1" />
<bean id="store" class="org.baeldung.store.Store">
<constructor-arg type="ItemImpl1" index="0" name="item" ref="item1" />
</bean>
</source>

Constructor-Based Dependency Injection - Revision history

Rasimsen: Created page with "In the case of constructor-based dependency injection, the container will invoke a constructor with arguments each representing a dependency we want to set. Spring resolves e..."