Spring @Bean
last modified October 18, 2023
In this article we show how to use @Bean annotation to declare beans in Java configuration classes.
Spring is a popular Java application framework for creating enterprise applications.
Spring @Bean
@Bean annotation indicates that the annotated method produces a bean to
be managed by the Spring container. It is a direct analog of the <bean/>
XML tag. @Bean supports most of the attributes offered by <bean/>,
such as: init-method, destroy-method, autowiring, lazy-init,
dependency-check, depends-on, scope.
Spring @Bean example
The application produces a Spring-managed bean with the @Bean annotation.
It also gives the bean some aliases.
pom.xml
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ ├───bean
│ │ │ HelloMessage.java
│ │ └───config
│ │ AppConfig.java
│ └───resources
│ logback.xml
│ messages.properties
└───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>beanannotation</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.
motd="Hello there!"
The messages.properties contains a message of the day property,
which is used by our HelloMessage bean. This gives the application
more flexibility and avoids hardcoding the message into the Java code.
package com.zetcode.bean;
public class HelloMessage {
private String message;
public HelloMessage(String message) {
this.message = message;
}
public String getMessage() {
return message;
}
}
The HelloMessage bean is created with a @Bean annotated
method.
package com.zetcode.config;
import com.zetcode.bean.HelloMessage;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
@Configuration
@PropertySource(value="messages.properties")
public class AppConfig {
@Value("${motd}")
private String message;
@Bean(name={"myMessage", "motd"})
public HelloMessage helloMessageProducer() {
var helloMessage = new HelloMessage(message);
return helloMessage;
}
}
We define a HelloMessage producer in the AppConfig.
@Configuration
@PropertySource(value="messages.properties")
public class AppConfig {
With @Configuration we declare that AppConfig is
a configuration class. The @PropertySource annotation allows us
to use properties from the messages.properties file easily with
@Value.
@Value("${motd}")
private String message;
We inject the motd property into the message attribute.
@Bean(name={"myMessage", "motd"})
public HelloMessage helloMessageProducer() {
var helloMessage = new HelloMessage(message);
return helloMessage;
}
The helloMessageProducer produces a new HelloMessage bean.
It takes its message from the external property. The @Bean annotation
makes the HelloMessage bean produced and managed by Spring.
In addition, we give the bean two aliases.
package com.zetcode;
import com.zetcode.bean.HelloMessage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
@ComponentScan(basePackages = "com.zetcode")
public class Application {
private static final Logger logger = LoggerFactory.getLogger(Application.class);
public static void main(String[] args) {
var ctx = new AnnotationConfigApplicationContext(Application.class);
var msgBean1 = ctx.getBean(HelloMessage.class);
logger.info("{}", msgBean1.getMessage());
var msgBean2 = (HelloMessage) ctx.getBean("myMessage");
logger.info("{}", msgBean2.getMessage());
var msgBean3 = (HelloMessage) ctx.getBean("motd");
logger.info("{}", msgBean3.getMessage());
ctx.close();
}
}
The application is annotated with @ComponentScan. The basePackages
option tells Spring to look for components in the com/zetcode package and
its subpackages.
var ctx = new AnnotationConfigApplicationContext(Application.class);
AnnotationConfigApplicationContext is a Spring standalone application context.
It accepts the annotated Application as an input; thus the scanning is
enabled.
var msgBean1 = ctx.getBean(HelloMessage.class);
logger.info("{}", msgBean1.getMessage());
We get the bean by its type.
var msgBean2 = (HelloMessage) ctx.getBean("myMessage");
logger.info("{}", msgBean2.getMessage());
var msgBean3 = (HelloMessage) ctx.getBean("motd");
logger.info("{}", msgBean3.getMessage());
Here we get the same bean by its aliases.
$ mvn -q exec:java 14:39:29.324 INFO com.zetcode.Application - "Hello there!" 14:39:29.324 INFO com.zetcode.Application - "Hello there!" 14:39:29.324 INFO com.zetcode.Application - "Hello there!"
We run the application.
In this article we have used the @Bean annotation to produce a
managed Spring bean.
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