Dependency Injection In Spring using constructor

* Dependency Injection refers to remove the dependency and make the code loosely coupled so that it is easy to test the code.

In such a case, we provide the information from the external source such as XML file. It makes our code loosely coupled and easier for testing. In such cases, we write the code as:

Two types of dependency injection are there.

1.Constructor Injection
    2.Setter Injection

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Constructor Injection (primitive type injection)
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This is the base class(abc.java)
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package com.sandeep.springDemo;

public class abc {

//String name;
int id;

public abc()
{
System.out.println("I am in abc");
}
public abc(int id)
{
//this.name=name;
this.id=id;
}

public void PrintDetail()
{
//System.out.println("name is" +name);
System.out.println("Id is "+id);
}

}

Main Class (MyApp.java)

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package com.sandeep.springDemo;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MyApp {

public static void main(String[] args)

{

ClassPathXmlApplicationContext context=

new ClassPathXmlApplicationContext("applicationContext.xml");

abc abc=context.getBean("MyABC",abc.class);

abc.PrintDetail();

context.close();

}

}

Spring configuration (applicationContext.xml)

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

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

    xmlns:context="http://www.springframework.org/schema/context"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context.xsd">

    <!-- Define your beans here -->

  

    

    <bean id="MyABC"

        class="com.sandeep.springDemo.abc">

    <constructor-arg value="25" type="int" />

</bean></beans>

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In the above code when we execute the MyApp.java  ,it will show the output Id is 25.

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explanation(Background work by spring):-
------------------------------

 <bean id="MyABC"

        class="com.sandeep.springDemo.abc">

    <constructor-arg value="25" type="int" />

</bean></beans>

In the above code,

<bean id="MyABC"  class="com.sandeep.springDemo.abc">
is simillar to
abc MyABC=new abc();

 <bean id="MyABC"

        class="com.sandeep.springDemo.abc">

    <constructor-arg value="25" type="int" />

</bean></beans>
is simillar to
abc MyABC=new abc(25);







If we did it normally then MyApp.java would contain

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package com.sandeep.springDemo;

public class MyAppNormal {

public static void main(String[] args) {

abc a=new abc(25);

a.PrintDetail();

}

}

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In the above code, we are hardcoding the object which is tightly coupled.Our intension is to make it loosely coupled using spring framework.

#Dependency Injection

#DependencyInjectionUsingSpring
#constructorDependencyInjection
#DependencyInjectionUsingConstructor