Monday, 13 August 2018

Spring bean configuration for inheritance [Base bean as a template]

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Mastering Base Bean Templates in Spring

In this guide, we're diving deep into a specialized feature of the Spring Framework: using a Base Bean as a Template. This is a game-changer for keeping your XML configurations clean and efficient.

What is a Base Bean Template?

Sometimes, you want to create a bean definition that serves purely as a blueprint for other beans. This base bean doesn't need to be instantiated itself; it just holds common properties that child beans will inherit.

The "abstract" Attribute

To tell Spring that a bean is a template and should not be created as an actual object, we use the abstract="true" attribute in the XML configuration. This is incredibly useful when:

You have many beans sharing the same properties (like a company name or database URL).
The parent bean doesn't have a complete configuration but provides a solid starting point.
You want to avoid the "No default constructor" error for parent beans that aren't meant to be used directly.

How to Implement This

In the video tutorial, we demonstrate how to define a parent bean with generic values and then use the parent attribute in child beans to pull those values in. If a child bean needs something different, it can easily override the template value with its own.

Key Benefits for Beginners

Reduces Code Duplication: Write your configuration once, and use it everywhere.
Easier Maintenance: Need to change a common value? Just update the template!
Cleaner XML: Your configuration files become much more readable.

Check Out More From My Channel

Explore these related tutorials to further master Spring Framework:

Click here to watch on Youtube:
https://www.youtube.com/watch?v=2dRalQGFMmA&list=UUhwKlOVR041tngjerWxVccw

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Spring bean configuration for inheritance [Base bean as a template]

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.2.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

Employee.java

package com.ram.model;

public class Employee

{

    private int id;

    private String name;

    private String countryName;

    public int getId()

    {

        return id;

    }

    public void setId(int id)

    {

        this.id = id;

    }

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public String getCountryName()

    {

        return countryName;

    }

    public void setCountryName(String countryName)

    {

        this.countryName = countryName;

    }

    @Override

    public String toString()

    {

        return "Employee [id=" + id + ", name=" + name + ", countryName="

                + countryName + "]";

    }

}

applicationContext.xml

<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-4.3.xsd">

    <bean id="baseEmployeeJapan" class="com.ram.model.Employee" abstract="true">

        <property name="countryName" value="Japan" />

    </bean>

    <bean id="employee1" class="com.ram.model.Employee" parent="baseEmployeeJapan">

        <property name="id" value="32" />

        <property name="name" value="Peter" />

    </bean>

    <bean id="employee2" class="com.ram.model.Employee" parent="baseEmployeeJapan">

        <property name="id" value="33" />

        <property name="name" value="John" />

    </bean>

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Employee employee1 = (Employee) context.getBean("employee1");

        System.out.println(

                "Got employee1 object from the ApplicationContext(Spring Container)");

        System.out.println(employee1);

        System.out.println("---------------------------------------");

        Employee employee2 = (Employee) context.getBean("employee2");

        System.out.println(

                "Got employee2 object from the ApplicationContext(Spring Container)");

        System.out.println(employee2);

    }

}

Output

Aug 03, 2018 9:33:27 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Fri Aug 03 09:33:27 IST 2018]; root of context hierarchy

Aug 03, 2018 9:33:27 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

---------------------------------------

Got employee1 object from the ApplicationContext(Spring Container)

Employee [id=32, name=Peter, countryName=Japan]

---------------------------------------

Got employee2 object from the ApplicationContext(Spring Container)

Employee [id=33, name=John, countryName=Japan]