Spring bean reference tutorial
last modified October 18, 2023
Spring bean reference tutorial shows how to refer to beans in a XML configuration file in a Spring application.
Spring is a popular Java application framework for creating enterprise applications.
Spring ref attribute
The ref attribute is a shortcut to the <ref> tag,
used to refer to other beans for injection.
Spring bean reference example
The application contains two beans: infoMessage and mesageRenderer.
The mesageRenderer refers to the infoMessage via the ref
attribute.
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ ├───bean
│ │ │ IMessage.java
│ │ │ InfoMessage.java
│ │ └───service
│ │ MessageRenderer.java
│ └───resources
│ logback.xml
│ my-beans.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>beanreference</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
and 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} [%thread] %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.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="infoMessage" class="com.zetcode.bean.InfoMessage"/>
<bean name="messageRenderer" class="com.zetcode.service.MessageRenderer">
<constructor-arg name="message" ref="infoMessage"/>
</bean>
</beans>
The my-beans.xml file declares two beans: info and
messageRenderer. The infoMessage refers to the infoMessage
via the ref attribute. Spring injects the infoMessage bean
into the message attribute via constructor injection.
package com.zetcode.bean;
public interface IMessage {
String getMessage();
}
The IMessage interface has one method declaration.
package com.zetcode.bean;
public class InfoMessage implements IMessage {
public String getMessage() {
return "This is information message";
}
}
The InfoMessage bean returns an information message.
package com.zetcode.service;
import com.zetcode.Application;
import com.zetcode.bean.IMessage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class MessageRenderer {
private static final Logger logger = LoggerFactory.getLogger(Application.class);
private IMessage message;
public MessageRenderer(IMessage message) {
this.message = message;
}
public void renderMessage() {
logger.info("{}", message.getMessage());
}
}
The MessageRenderer renders a message. It expects one bean to be
injected. Spring injects the infoMessage bean into the
MessageRenderer via constructor injection.
package com.zetcode;
import com.zetcode.service.MessageRenderer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.GenericXmlApplicationContext;
public class Application {
private static final Logger logger = LoggerFactory.getLogger(Application.class);
public static void main(String[] args) {
var ctx = new GenericXmlApplicationContext("my-beans.xml");
var renderer = (MessageRenderer) ctx.getBean("messageRenderer");
renderer.renderMessage();
ctx.close();
}
}
This is the main application class. It retrieves the MessageRenderer bean
and call its renderMessage method.
$ mvn -q exec:java 12:05:23.567 [com.zetcode.Application.main()] INFO com.zetcode.Application - This is information message
We run the application.
In this article we have shown how to refer to other beans with Spring's XML
ref attribute.
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