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.

<?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.

<?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.

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.

<?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.

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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