Spring Framework dependency injection

Spring core

We will discuss the following topic.

Spring IOC

Dependency Injection

Spring Framework benefits in the form of Spring IOC.

Spring framework says you are a developer, so don’t waste your time creating and managing the object.

I can create objects for you.

I can manage objects for you and help our application to be Configurable.

As well it’s managing dependencies also.

So, we can say spring relay helps us manage the time as well.

Basically IOC provides to us – Without touching source code we can change the implementation using xml file.

It takes care of injecting the dependency also.

IOC Container – Spring having own container

Below is the diagram that shows if we create entities in an xml file for class a , b, c according to the spring container will create objects for us to use.

  Types of IOC Container

 How actually, it’s creating objects internally using Application Context Type Container.

Example Spring IOC-

Step by step

First we will create Interface - SIM

package com.javaupgradIoc.com;
public interface Sim {
  void calling();
  void data();
}

Second we will create two classes and implement Sim interface

package com.javaupgradIoc.com;
public class RelianceJIO implements Sim{
	@Override
	public void calling() {		
		System.out.println("calling using Reliance sim");	
	}
	@Override
	public void data() {
		// TODO Auto-generated method stub
		System.out.println("Internet using Reliance sim");
	}
}

package com.javaupgradIoc.com;
public class Airtel implements Sim{
	public Airtel() {
		// TODO Auto-generated constructor stub
		System.out.println("Airtel constructor");
	}
	@Override
	public void calling() {
		// TODO Auto-generated method stub
		System.out.println("Calling using airtel sim");
	}
	@Override
	public void data() {
		// TODO Auto-generated method stub
		System.out.println("Internet using airtel sim");
	}
}

Now Create a main class and configurable class 

package com.javaupgradIoc.com;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
	public static void main(String[] args) {
		ApplicationContext context=new ClassPathXmlApplicationContext("beans.xml");
		System.out.println("config loaded");
		Sim sim=context.getBean("sim",Sim.class);//  using interface
		sim.calling();
		sim.data();	
	}
}

getBean() – method use for injecting the object through IOC container 

beans.XML file name

IN xml based configuration , xml file supplies the metadata for the spring container ton manage the bean.

<?xml version="1.0" encoding="UTF-8"?>

<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.xsd"> 

        <bean id="sim" class="com.javaupgradIoc.com.RelianceJIO"></bean>

</beans>

Its work internally look like - Sim sim=new RelianceJIO();

Sim sim=context.getBean("sim",Sim.class);//  using interface we inject this id 

OutPUT –

config loaded

calling using Reliance sim

Internet using Reliance sim

Spring Dependency Injection-

Spring will be going to inject our dependency. 

In this diagram you can see class Family, class Job and collection in the form of numbers.

So these all are dependencies for Class me.

These all are dependencies

Please don’t do hard code – spring will going to inject your dependencies

Spring dependencies types

1. First Example using setter injection 

package com.javaupgrad.di;
public class Student {
	private String studentName;
	public void setStudentName(String studentName) {
		this.studentName = studentName;
	}
	public void displayStudentInfo() {
		System.out.println("student name is "+studentName);
	}
}

Now we will create Exam class or configurable class

package com.javaupgrad.di;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.javaupgradIoc.com.Sim;
public class Exam {
	public static void main(String[] args) {
		ApplicationContext context=new ClassPathXmlApplicationContext("beansdi.xml");
		Student abhi=context.getBean("student", Student.class);
		abhi.displayStudentInfo();
	}
}

Then , we will create xml file 

Note:-When we use setter type injection in spring, so that time we use Property tag

<?xml version="1.0" encoding="UTF-8"?>

<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.xsd"> 

<bean id="student" class="com.javaupgrad.di.Student">

<property name="studentName"  value="Abhilash"    />

</bean>

</beans>

OUtPUt

student name is Abhilash

2. Constructor type injection

First Example using Constructor injection 

package com.javaupgrad.constructdi;
public class Student {
	private int id;
	private String studentName;
	public Student(int id,String studentName){
		System.out.println("constructor ");
		this.id=id;
		this.studentName=studentName;
	}
	public void displayStudentInfo() {
		// TODO Auto-generated method stub
		System.out.println("Student name is: " +studentName +"  and the id is  " +id);
	}
}	

package com.javaupgrad.constructdi;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.javaupgradIoc.com.Sim;
public class Exam {
	public static void main(String[] args) {
		ApplicationContext context=new ClassPathXmlApplicationContext("beanscons.xml");
		Student abhi=context.getBean("student", Student.class);
		abhi.displayStudentInfo();
	}
}

Note:-When we use setter type injection in spring, so that time we use Constructor tag

<?xml version="1.0" encoding="UTF-8"?>

<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.xsd"> 

<bean id="student" class="com.javaupgrad.constructdi.Student">

<constructor-arg name="studentName" value="abhilash" />

<constructor-arg name="id" value="1" />

</bean>

</beans>