Spring 5 IoC Example with application Context XML (ClassPathXmlApplicationContext) and Gradle.

It's year 2023 and one may not use the XML based Spring Application Context for new projects in production, but there are few reasons why its still relevant,

• Working on a legacy product: If you are working on a legacy product that uses an older version of Spring or a configuration file written in XML format, you may need to use ClassPathXmlApplicationContext to initialize the Spring application context.
• Learning Spring: If you are new to Spring and want to learn how it works, starting with ClassPathXmlApplicationContext is a good option. It is a simple way to set up a Spring application context using an XML configuration file, and it can help you understand the basic concepts of Spring.
• Limited resources constraint: If you are working on a project with limited resources, using ClassPathXmlApplicationContext is a good option as it has a smaller footprint compared to other Spring container implementations like AnnotationConfigApplicationContext.
• Testing: ClassPathXmlApplicationContext is also commonly used in testing scenarios, where it can be used to create a lightweight Spring context for testing individual components of a larger Spring application.
• Integrating with other frameworks: In some cases, other frameworks may require the use of ClassPathXmlApplicationContext to integrate with Spring. For example, some legacy ORM frameworks may require configuration via an XML file and integration with Spring through ClassPathXmlApplicationContext.
• Limited deployment options: Some cloud deployment platforms may not support certain newer Spring container implementations, in which case ClassPathXmlApplicationContext can be used as a fallback option.

Let us take a example of IoC using a Interface Teacher and its implementations like MathTeacher and ScienceTeacher.

Teacher.java

package example.spring_ioc_with_xml;

/**
 * Our interface to learn
 * String IoC using XML 
 * based ClassPathXmlApplicationContext
 * 
 */
public interface Teacher {

    String doStudies();
}

ScienceTecher.java

package example.spring_ioc_with_xml;

public class ScienceTeacher implements Teacher {
    @Override
    public String doStudies() {
        return "Let us study chapter 'Work & Energy'!";
    }
}

MathTecher.java

package example.spring_ioc_with_xml;

public class MathTeacher implements Teacher {
    @Override
    public String doStudies() {
        return "Let us study chapter 'Quadratic Equations'!";
    }
}

MusicTeacher.java

package example.spring_ioc_with_xml;

public class MusicTeacher implements Teacher {
    @Override
    public String doStudies() {
        return "Let us learn how to play Guitar!";
    }
}

Now lets create our ApplicationContext.xml file.

<?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">

  <bean id="mathTeacher" class="example.spring_ioc_with_xml.MathTeacher"/>
  <bean id="scienceTeacher" class="example.spring_ioc_with_xml.ScienceTeacher" />
  <bean id="musicTeacher" class="example.spring_ioc_with_xml.MusicTeacher" />

</beans>

And its time to create a Main class with the implementation of ClassPathXmlApplicationContext to perform IoC.

package example.spring_ioc_with_xml;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {

    public static void main(String[] args) {

        ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");

        Teacher teacher = classPathXmlApplicationContext.getBean("scienceTeacher", ScienceTeacher.class);
        String scienceTeachersMessage = teacher.doStudies();
        System.out.println(scienceTeachersMessage);

        teacher = classPathXmlApplicationContext.getBean("mathTeacher", MathTeacher.class);
        System.out.println(teacher.doStudies());

        teacher = classPathXmlApplicationContext.getBean("musicTeacher", MusicTeacher.class);
        System.out.println(teacher.doStudies());

    }
}

Output:

Note:

Make sure to add the below dependency in your build.gradle dependencies.

implementation group: 'org.springframework', name: 'spring-context', version: '5.3.22'