Spring Boot XML Configuration Example

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In this article, we will quickly discuss how to develop a simple Spring boot application using XML-based Spring configuration.

In this example, we don't use either Annotation-based configuration or Java-based configuration, we only use XML-based configuration to create and configure beans.

Overview

Spring provides a @ImportResource annotation to load beans from an applicationContext.xml file into an Application Context.

@ImportResource({"classpath*:applicationContext.xml"})

In this example, we are creating a simple message-processing spring boot application. Here we are sending a message using different services like SMSService, TwitterService, and EmailService. We will configure message service beans in the applicationContext.xml file and we will load beans using @ImportResource annotation as:

@SpringBootApplication
@ImportResource({"classpath*:applicationContext.xml"})
public class Springboot2XmlConfigApplication {
    public static void main(String[] args) {
        ApplicationContext applicationContext = SpringApplication.run(Springboot2XmlConfigApplication.class, args);

        MessageProcessor userService = applicationContext.getBean(MessageProcessor.class);
        userService.processMsg("twitter message sending ");
    }
}

While there are multiple ways of doing this, the recommended way is to create a separate configuration class to load this XML bean definition file.

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

The key part of the definition is @ImportResource({" classpath*:applicationContext.xml"}). 

 
Let's create a complete simple spring boot example to demonstrate how to set up an XML-based configuration.

1. Setup

Let's quickly create a Spring Boot application using Spring Initializr at http://start.spring.io/, which is an online Spring Boot application generator.

Add this Maven dependency in the pom.xml file:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Here is the project structure or packaging structure for your reference:

2. Create Interfaces and Classes

In this example, we are sending messages using different services like SMSService, TwitterService, and EmailService. 

MessageService.java

Let's create a MessageService interface with the following content:

public interface MessageService {
    public void sendMsg(String message);
}

EmailService.java

Let's create an EmailService class that implements the MessageService interface and its method:

public class EmailService implements MessageService {

    public void sendMsg(String message) {
        System.out.println(message);
    }
}

SMSService.java

Let's create the SMSService class that implements the MessageService interface and its method:

public class SMSService implements MessageService {

    public void sendMsg(String message) {
        System.out.println(message);
    }
}

TwitterService.java

Let's create the TwitterService class that implements the MessageService interface and its method:

public class TwitterService implements MessageService {

    public void sendMsg(String message) {
        System.out.println(message);
    }
}

MessageProcessor.java

Let's create a MessageProcessor interface with the following content:

public interface MessageProcessor {
    public void processMsg(String message);
}

MessageProcessorImpl.java

Let's create the MessageProcessorImpl class that implements the MessageProcessor interface and its method:

public class MessageProcessorImpl implements MessageProcessor {

    private MessageService messageService;

    public void setMessageService(MessageService messageService) {
        this.messageService = messageService;
    }

    public void processMsg(String message) {
        messageService.sendMsg(message);
    }
}

3. The applicationContext.xml File

Let's create and configure Spring beans in the 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="emailService"
  class="net.guides.springboot2.springboot2xmlconfig.service.EmailService" />
	<bean id="sMSService"
  class="net.guides.springboot2.springboot2xmlconfig.service.SMSService" />
	<bean id="twitterService"
  class="net.guides.springboot2.springboot2xmlconfig.service.TwitterService" />
	<bean id="messageProcessor"
  class="net.guides.springboot2.springboot2xmlconfig.service.MessageProcessorImpl">
		<property name="messageService" ref="twitterService"></property>
	</bean>
</beans>

4. Running Application

This spring boot application has an entry point Java class called Springboot2XmlConfigApplication.java with the public static void main(String[] args) method, which you can run to start the application.

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.ImportResource;

import net.guides.springboot2.springboot2xmlconfig.service.MessageProcessor;

@SpringBootApplication
@ImportResource({
    "classpath*:applicationContext.xml"
})
public class Springboot2XmlConfigApplication {

    public static void main(String[] args) {
        ApplicationContext applicationContext = SpringApplication.run(Springboot2XmlConfigApplication.class, args);

        MessageProcessor userService = applicationContext.getBean(MessageProcessor.class);
        userService.processMsg("twitter message sending ");
    }
}

Output:

Master Spring Boot with Source Code on GitHub - Spring Boot Tutorial 

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