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Spring @Bean annotation tutorial

Spring @Bean annotation tutorial shows 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.

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>beanannotation</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
        <spring-version>5.1.3.RELEASE</spring-version>

    </properties>

    <dependencies>

        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</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>1.6.0</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/message.properties
motd="Hello there!"

The message.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.

com/zetcode/bean/HelloMessage.java
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.

com/zetcode/config/AppCofig.java
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.

com/zetcode/Application.java
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 tutorial, we have used the @Bean annotation to produce a managed Spring bean.

You might also be interested in these related tutorials: Spring Singleton scope bean, Spring @ComponentScan tutorial, Spring @Autowired tutorial, Java tutorial, or list all Spring tutorials.