Spring 3.x framework provides support for moving the bean definitions out of the XML file into the Java class. This tutorial will explore the Spring-specific @Configuration annotation for spring annotation based configuration.
1. Introduction
- Spring is an open-source framework created to address the complexity of an enterprise application development
- One of the chief advantages of the Spring framework is its layered architecture, which allows the developer to be selective about which of its components they can use while providing a cohesive framework for
J2EEapplication development - Spring framework provides support and integration to various technologies for e.g.:
- Support for Transaction Management
- Support for interaction with the different databases
- Integration with the Object Relationship frameworks for e.g. Hibernate, iBatis etc
- Support for Dependency Injection which means all the required dependencies will be resolved with the help of containers
- Support for
RESTstyle web-services
1.1 @Configuration annotation in spring
The @Configuration annotation in spring help in the annotation-based configuration. Implementing this annotation declares a class provides one or more @Bean methods and may be used by the spring container to generate the bean definitions and serve requests for those beans at runtime. Below snippet shows how to include this annotation in the java class.
Code Snippet
@Configuration
public class ApplicationConfig {
@Bean
public MyClass getService() {
// Do something.
}
@Bean
public MyClass1 getService() {
// Do something.
}
}
Now, open up the Eclipse IDE and let us see how to implement this annotation in the spring framework!
2. Spring @Configuration Annotation Example
Here is a systematic guide for implementing this tutorial in the spring framework.
2.1 Tools Used
We are using Eclipse Kepler SR2, JDK 8, MySQL and Maven. Having said that, we have tested the code against JDK 1.7 and it works well.
2.2 Project Structure
Firstly, let us review the final project structure, in case you are confused about where you should create the corresponding files or folder later!
2.3 Project Creation
This section will demonstrate how to create a Java-based Maven project with Eclipse. In Eclipse IDE, go to File -> New -> Maven Project.
In the New Maven Project window, it will ask you to select a project location. By default, ‘Use default workspace location’ will be selected. Select the ‘Create a simple project (skip archetype selection)’ checkbox and just click on the next button to proceed.
It will ask you to ‘Enter the group and the artifact id for the project’. We will input the details as shown in the below image. The version number will be by default: 0.0.1-SNAPSHOT.
Click on Finish and the creation of a maven project is completed. If you observe, it has downloaded the maven dependencies and a pom.xml file will be created. It will have the following code:
pom.xml
<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>com.spring</groupId> <artifactId>SpringConfigurationAnnotation</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> </project>
We can start adding the dependencies that developers want like Spring Core, Spring Context etc. Let us start building the application!
3. Application Building
Below are the steps involved in developing this application.
3.1 Maven Dependencies
Here, we specify the dependencies for the spring framework. Maven will automatically resolve the rest dependencies such as Spring Beans, Spring Core etc. The updated file will have the following code:
pom.xml
<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>com.spring</groupId> <artifactId>SpringConfigurationAnnotation</artifactId> <version>0.0.1-SNAPSHOT</version> <name>Spring Configuration Annotation Example</name> <description>javacodegeek.com</description> <dependencies> <!-- https://mvnrepository.com/artifact/org.springframework/spring-core --> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>5.1.0.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>5.1.0.RELEASE</version> </dependency> </dependencies> </project>
3.2 Java Class Creation
Let us write the Java classes involved in this application.
3.2.1 Implementation of Bean class
Add the following code to the bean definition:
Country.java
package com.spring;
public class MyBeanImpl implements MyBean {
public String getBeanName() {
return "My service bean.";
}
}
3.2.2 Implementation of Configuration class
Annotate this class with the @Configuration annotation to tell spring about the configuration file and define the bean via @Bean annotation. Add the following code to it:
AppConfig.java
package com.spring.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.spring.MyBean;
import com.spring.MyBeanImpl;
@Configuration
public class AppConfig {
@Bean
public MyBean getBeanName() {
return new MyBeanImpl();
}
}
3.2.3 Implementation of Utility Class
The implementation class will be able to configure the bean for further implementation. Add the following code to it:
AppMain.java
package com.spring.util;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import com.spring.MyBean;
import com.spring.config.AppConfig;
public class AppMain {
public static void main(String[] args) {
AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(AppConfig.class);
// getting the bean definition!
MyBean bean = ac.getBean(MyBean.class);
System.out.println(bean.getBeanName());
// closing the context object!
ac.close();
}
}
4. Run the Application
To execute the application, right click on the AppMain class, Run As -> Java Application. Developers can debug the example and see what happens after every step. Enjoy!
5. Project Demo
The code shows the following log as the output of this tutorial.
My service bean.
That is all for this tutorial and I hope the article served you whatever you were looking for. Happy Learning and do not forget to share!
6. Conclusion
This post defines the @Configuration in the spring framework and helps developers understand the basic configuration required to achieve this. Developers can download the sample application as an Eclipse project in the Downloads section.
7. Download the Eclipse Project
This was an example of Spring @Configuration Annotation for beginners.
You can download the full source code of this example here: SpringConfigurationAnnotation
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