Spring BeanFactory tutorial

last modified October 18, 2023

Spring BeanFactory tutorial shows how use BeanFactory to work with beans in a Spring application

Spring is a popular Java application framework for creating enterprise applications.

Spring BeanFactory

BeanFactory is a central registry of application components. It centralizes configuration of application components. BeanFactory loads bean definitions stored in a configuration source such as an XML document or a Java configuration.

Spring BeanFactory example

The application creates a bean factory, loads bean definitions from an XML configuration file and applies a post processor on the beans.

pom.xml src ├───main │ ├───java │ │ └───com │ │ └───zetcode │ │ Application.java │ └───resources │ database.properties │ logback.xml │ my-beans.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>beanfactory</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>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</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, spring-jdbc, 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/database.properties

db.url=jdbc:h2:mem:testdb db.username=testuser db.password=s$cret

These properties are going to be inserted into a bean with a bean post processing factory.

resources/my-beans.xml

<?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="dataSource" class="org.springframework.jdbc.datasource.SimpleDriverDataSource">
    <property name="url" value="${db.url}"></property>
    <property name="username" value="${db.username}"></property>
    <property name="password" value="${db.password}"></property>
</bean>

</beans>

The my-beans.xml file declares a dataSource bean. The ${} syntax inserts values from an external properties file.

com/zetcode/Application.java

package com.zetcode;

import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer; import org.springframework.beans.factory.support.DefaultListableBeanFactory; import org.springframework.beans.factory.xml.XmlBeanDefinitionReader; import org.springframework.core.io.ClassPathResource; import org.springframework.jdbc.datasource.SimpleDriverDataSource;

public class Application {

private static final Logger logger = LoggerFactory.getLogger(Application.class);

public static void main(String[] args) {

    var factory = new DefaultListableBeanFactory();
    var reader = new XmlBeanDefinitionReader(factory);
    reader.loadBeanDefinitions(new ClassPathResource("my-beans.xml"));

    var cfg = new PropertyPlaceholderConfigurer();
    cfg.setLocation(new ClassPathResource("database.properties"));
    cfg.postProcessBeanFactory(factory);

    var dataSource = (SimpleDriverDataSource) factory.getBean("dataSource");

    logger.info("Url: {}", dataSource.getUrl());
    logger.info("User name: {}", dataSource.getUsername());
    logger.info("Password: {}", dataSource.getPassword());
}

}

The application creates a BeanFactory and registers a bean.

var factory = new DefaultListableBeanFactory(); var reader = new XmlBeanDefinitionReader(factory); reader.loadBeanDefinitions(new ClassPathResource(“my-beans.xml”));

A DefaultListableBeanFactory, which is an implementation of the BeanFactory, is created. It reads beans from my-beans.xml configuration file with XmlBeanDefinitionReader. The bean definitions are loaded with loadBeanDefinitions.

var cfg = new PropertyPlaceholderConfigurer(); cfg.setLocation(new ClassPathResource(“database.properties”)); cfg.postProcessBeanFactory(factory);

The PropertyPlaceholderConfigurer inserts properties into the bean from the database.properties file.

var dataSource = (SimpleDriverDataSource) factory.getBean(“dataSource”);

We get the bean from the factory with getBean.

logger.info(“Url: {}”, dataSource.getUrl()); logger.info(“User name: {}”, dataSource.getUsername()); logger.info(“Password: {}”, dataSource.getPassword());

We retrieve the dataSource bean attributes.

$ mvn -q exec:java 10:02:30.701 INFO com.zetcode.Application - Url: jdbc:h2:mem:testdb 10:02:30.701 INFO com.zetcode.Application - User name: testuser 10:02:30.701 INFO com.zetcode.Application - Password: s$cret

We run the application.

In this article we have shown how a BeanFactory is created and how bean definitions are loaded and post processed.

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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