Using XML Configuration in Spring Boot Applications

Spring Boot 3 primarily favors annotation-based configuration for its simplicity and maintainability. However, there are scenarios where you might need to integrate existing XML configurations into your application. This tutorial demonstrates how to achieve this using a @Configuration class and the @ImportResource annotation.

Firstly, if you are new to Spring Boot Configuration, check this article: Configuring Spring Boot applications

Project Setup:

1. Create a new Spring Boot project using your preferred IDE or Spring Initializr.
2. Within the src/main/java directory, create the following packages:
   • com.example.demo

Java Classes:

Create a Java class named MyService.java under com.example.demo:

package com.example.demo;

public class MyService {

    private String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

Create a Java class named XmlConfiguration.java under com.example.demo:

package com.example.demo;

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ImportResource;

@Configuration
@ImportResource({"classpath*:applicationContext.xml"})
public class XmlConfiguration {
}

Define Spring Boot XML Configuration

Create an XML file named applicationContext.xml under src/main/resources:

<?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="myService" class="com.example.demo.MyService">
        <property name="message" value="Hello from XML configuration!" />
    </bean>

</beans>

Explanation:

• XmlConfiguration.java:
  • @Configuration: Marks this class as a Spring configuration class.
  • @ImportResource: This annotation instructs Spring Boot to import bean definitions from the specified resource(s). In this case, we reference classpath:applicationContext.xml.
• applicationContext.xml:
  • XML schema declarations: Specify the locations of Spring Bean schema files.
  • <bean id="myService">: Defines a bean with the ID “myService” and specifies its class as com.example.demo.MyService.
  • <property name="message">: Sets the “message” property of the bean with the specified value.

Here is the project structure:

Running the Application:

1. Ensure you have Maven or Gradle configured for your project.
2. Run the Spring Boot application using your preferred method (e.g., mvn spring-boot:run for Maven).

Verification:

Use your favorite debugger or logging framework to verify that the MyService bean is indeed created and configured with the message “Hello from XML configuration!”.

Important Note:

While XML configuration offers flexibility, Spring Boot encourages the use of annotation-based configuration for its advantages in maintainability and IDE support. Consider migrating existing XML configurations to annotations whenever possible.

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