Monday, 13 August 2018

Spring bean configuration for inheritance

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Spring Bean Inheritance Explained

Welcome to another Spring tutorial! Today, we are exploring a concept that makes your XML configurations cleaner and much more manageable: Spring Bean Inheritance. If you've ever found yourself repeating the same property values across multiple beans, this is exactly what you need.

1. What is Configuration Inheritance?

In Spring, a bean definition can contain a lot of information, like property values and constructor arguments. Instead of redefining these for every single bean, you can create a "Parent Bean" that holds common values. Other beans (the "Child Beans") can then inherit these values automatically.

2. Using the 'parent' Attribute

To implement this, Spring provides a simple attribute called parent. When you specify a parent for a bean, the child bean inherits all the property values from that parent. It’s like a template that saves you from writing repetitive code.

3. The Power of Overriding

The best part about inheritance is flexibility. While a child bean inherits everything from the parent, it also has the power to override specific properties. If a child bean needs a different value for one particular property, you just define it in the child bean, and Spring will use that instead of the parent's value.

Why is this helpful for Beginners?

Less Typing: You don't have to repeat code.
Fewer Errors: Changing a common value in one place (the parent) updates it everywhere.
Better Organization: It makes your Spring configuration files much easier to read and understand.

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Spring bean configuration for inheritance

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">

        <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 01, 2018 9:57:05 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Wed Aug 01 09:57:05 IST 2018]; root of context hierarchy

Aug 01, 2018 9:57:05 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]