Spring @Configuration tutorial
last modified October 18, 2023
Spring @Configuration annotation tutorial shows how to configure Spring application using @Configuration annotation.
Spring is a popular Java application framework for creating enterprise applications.
Spring @Configuration
@Configuration annotation is used for Spring annotation based configuration.
The @Configuration is a marker annotation which indicates that a class
declares one or more @Bean methods and may be processed
by the Spring container to generate bean definitions and service requests for
those beans at runtime
Spring @Configuration example
The following application uses @Configuration to configure a Spring
application.
pom.xml
src
└───src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ └───config
│ │ AppConfig.java
│ │ H2Configurer.java
│ └───resources
│ application.properties
│ logback.xml
└───test
└───java
This is the project structure.
<?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>com.zetcode</groupId>
<artifactId>configurationex</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
<spring-version>5.3.23</spring-version>
</properties>
<dependencies>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.4.0</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring-version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring-version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<mainClass>com.zetcode.Application</mainClass>
</configuration>
</plugin>
</plugins>
</build>
</project>
In the pom.xml file, we have basic Spring dependencies spring-core,
spring-context, and logging logback-classic dependency.
The exec-maven-plugin is used for executing Spring application from the
Maven on the command line.
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<logger name="org.springframework" level="ERROR"/>
<logger name="com.zetcode" level="INFO"/>
<appender name="consoleAppender" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<Pattern>%d{HH:mm:ss.SSS} %blue(%-5level) %magenta(%logger{36}) - %msg %n
</Pattern>
</encoder>
</appender>
<root>
<level value="INFO" />
<appender-ref ref="consoleAppender" />
</root>
</configuration>
The logback.xml is a configuration file for the Logback logging library.
app.name=My application app.db=H2
Here we have some application properties.
package com.zetcode.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
@Configuration
@ComponentScan(basePackages = "com.zetcode")
@PropertySource(value = "application.properties")
public class AppConfig {
@Bean
public H2Configurer databaseConfig() {
return new H2Configurer();
}
}
AppConfig is the application configuration class. It is
decorated with the @Configuration annotation, which is a specialization
of the @Component.
@Configuration
@ComponentScan(basePackages = "com.zetcode")
@PropertySource(value = "application.properties")
public class AppConfig {
Component scanning is enabled with @ComponentScan and the resources
are loaded with @PropertySource.
@Bean
public H2Configurer databaseConfig() {
return new H2Configurer();
}
With @Bean annotation, we create a H2Configurer bean.
package com.zetcode.config;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class H2Configurer {
private static final Logger logger = LoggerFactory.getLogger(H2Configurer.class);
public H2Configurer() {
logger.info("Configuring H2 database");
}
}
The H2Configurer simply logs a message.
package com.zetcode;
import com.zetcode.config.AppConfig;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.stereotype.Component;
@Component
public class Application {
private static final Logger logger = LoggerFactory.getLogger(Application.class);
public static void main(String[] args) {
var ctx = new AnnotationConfigApplicationContext(AppConfig.class);
var app = ctx.getBean(Application.class);
app.run();
ctx.close();
}
@Value("${app.name}")
private String applicationName;
@Value("${app.db}")
private String database;
private void run() {
logger.info("Application name: {}", applicationName);
logger.info("Database: {}", database);
}
}
The application class prints the application properties. The properties are
injected into the attributes with @Value.
var ctx = new AnnotationConfigApplicationContext(AppConfig.class);
The AppConfig is loaded into the application context.
$ mvn -q exec:java 20:07:39.769 INFO com.zetcode.config.H2Configurer - Configuring H2 database 20:07:39.801 INFO com.zetcode.Application - Application name: My application 20:07:39.816 INFO com.zetcode.Application - Database: H2
We run the application.
In this article we have configured a Spring application with @Configuration.
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