Spring Boot and Microservices Roadmap for Beginners

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Spring @ImportResource Annotation Example

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In this article, we will quickly discuss how to use @ImportResource annotation with a simple Spring boot application.
Spring provides a @ImportResource annotation is used 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 an 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"}). The applicationContext.xml will be imported from the classpath.
Let's create a complete simple spring boot example to demonstrate how to set up XML based configuration.

Create and Import Spring Boot application

Let's quickly create a Spring Boot application using Spring Initializr at http://start.spring.io/, which is an online Spring Boot application generator.
Please refer the project structure as in below diagram.

The pom.xml File

<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>

 <groupId>net.guides.springboot2</groupId>
 <artifactId>springboot2-xml-config</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <packaging>jar</packaging>

 <name>springboot2-xml-config</name>
 <description>Demo project for Spring Boot</description>

 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.0.4.RELEASE</version>
  <relativePath/> <!-- lookup parent from repository -->
 </parent>

 <properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
  <java.version>1.8</java.version>
 </properties>

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

  <dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-test</artifactId>
   <scope>test</scope>
  </dependency>
 </dependencies>

 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>
</project>
Let's create Message POJO class with few service class for demonstration. In this example, we are sending messages using different services like SMSService, TwitterService, and EmailService.

Message.java

package net.guides.springboot2.springboot2xmlconfig.model;

public class Message {
 private int id;
 private String message;
 public Message(int id, String message) {
  super();
  this.id = id;
  this.message = message;
 }
}

MessageService.java

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

EmailService.java

import org.springframework.stereotype.Service;

public class EmailService implements MessageService{

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

}

SMSService.java

import org.springframework.stereotype.Service;

public class SMSService implements MessageService{

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

}

TwitterService.java

import org.springframework.stereotype.Service;

public class TwitterService implements MessageService{

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

}

MessageProcessor.java

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

MessageProcessorImpl.java

package net.guides.springboot2.springboot2xmlconfig.service;

public class MessageProcessorImpl implements MessageProcessor {

 private MessageService messageService;

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

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

The applicationContext.xml File

Let's create and configure Spring beans in 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>

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.
package net.guides.springboot2.springboot2xmlconfig;

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


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