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.

pom.xml

<?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.

resources/logback.xml

<?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.

resources/application.properties

app.name=My application app.db=H2

Here we have some application properties.

com/zetcode/config/AppConfig.java

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.

com/zetcode/config/H2Configurer.java

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.

com/zetcode/Application.java

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.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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