Spring Dependency Injection

Dependency Injection is the main functionality provided by Spring IOC(Inversion of Control). The Spring-Core module is responsible for injecting dependencies through either Constructor or Setter methods.

***Setter Dependency Injection (SDI): ***

This is the simpler of the two DI methods. In this, the DI will be injected with the help of setter and/or getter methods. Now to set the DI as SDI in the bean, it is done through the bean-configuration file For this, the property to be set with the SDI is declared under the property tag in the bean-config file.

package com.rmavuluri.org;
 
import com.rmavuluri.org.IEmployee;
 
public class EmployeeBean {
 
    // The object of the interface IEmployee
    IEmployee employee;
 
    // Setter method for property employee
    public void setEmployee(IEmployee employee){
        this.employee = employee;
    }
}

<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
 
    <bean id="EmployeeBean" class="com.rmavuluri.org.IEmployee">
        <property name="employee">
            <ref bean="TESTEMPLOY" />
        </property>
    </bean>   
    <bean id="TESTEMPLOY" class="com.rmavuluri.org.impl.TESTEMPLOY" />
</beans>

***Constructor Dependency Injection (CDI): ***

In this, the DI will be injected with the help of constructors. Now to set the DI as CDI in bean, it is done through the bean-configuration file For this, the property to be set with the CDI is declared under the constructor-arg tag in the bean-config file.

package com.rmavuluri.org;
 
import com.rmavuluri.org.IEmployee;
 
public class EmployeeBean {
 
    // The object of the interface IEmployee
    IEmployee employee;
 
    // Setter method for property employee
    public void setEmployee(IEmployee employee){
        this.employee = employee;
    }
}

<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
 
    <bean id="GFG" class="com.rmavuluri.org.EmployeeBean">
        <constructor-arg>
            <bean class="com.rmavuluri.org.impl.TESTEMPLOY" />
        </constructor-arg>
    </bean>
     
<bean id="Testemployee" class="com.rmavuluri.org.impl.TESTEMPLOY" />
</beans>