Spring Boot 2 Java Based Configuration Example - RameshMF/spring-boot-developers-guide GitHub Wiki

In this article, we will quickly discuss how to develop a simple Spring boot 2 application using Java-based configuration.

We use @Configuration and @Bean annotations to develop spring boot 2 standalone in-memory application. Note that we haven't used @Service or @Component annotation in this example. (annotation based configuration)

2. Tools and Technologies Used

  • Spring Boot - 2.0.4.RELEASE
  • JDK - 1.8 or later
  • Spring Framework - 5.0.8 RELEASE
  • Maven - 3.2+
  • IDE - Eclipse or Spring Tool Suite (STS)

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.

package structure 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-annotation-config</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>springboot2-annotation-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>

Create few Services using @Service Annotation

Note that we haven't used @Service or @Component annotations.

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);
	}

}

UserService.java

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

UserServiceImpl.java

package net.guides.springboot2.springboot2annotationconfig.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

public class UserServiceImpl implements UserService {

	@Autowired
	@Qualifier("TwitterService")
	private MessageService messageService;

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

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

Running Application

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

In this file, we have used @Bean annotation to create bean programatically(using new keyword).

package net.guides.springboot2.springboot2annotationconfig;

package net.guides.springboot2.springboot2javaconfig;

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

import net.guides.springboot2.springboot2javaconfig.service.EmailService;
import net.guides.springboot2.springboot2javaconfig.service.MessageProcessor;
import net.guides.springboot2.springboot2javaconfig.service.MessageProcessorImpl;
import net.guides.springboot2.springboot2javaconfig.service.MessageService;
import net.guides.springboot2.springboot2javaconfig.service.SMSService;
import net.guides.springboot2.springboot2javaconfig.service.TwitterService;

@SpringBootApplication
public class Springboot2JavaConfigApplication {

	@Bean(name = "emailService")
	public MessageService emailService() {
		return new EmailService();
	}

	@Bean(name = "smsService")
	public MessageService smsService() {
		return new SMSService();
	}

	@Bean(name = "twitterService")
	public MessageService twitterService() {
		return new TwitterService();
	}

	@Bean
	public MessageProcessor messageProcessor() {
		return new MessageProcessorImpl(twitterService());
	}

	public static void main(String[] args) {
		ApplicationContext applicationContext = SpringApplication.run(Springboot2JavaConfigApplication.class, args);
		MessageProcessor userService = applicationContext.getBean(MessageProcessor.class);
		userService.processMsg("twitter message sending ");
	}
}

Output

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