Ebooks

Spring BeanFactory tutorial

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>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>

        <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>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, 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 tutorial, we have shown how a BeanFactory is created and how bean definitions are loaded and post processed.

You might also be interested in these related tutorials: Spring BeanDefinitionBuilder tutorial, Spring Singleton scope bean, Spring inject List XML tutorial, Spring BeanDefinitionBuilder tutorial, Spring HikariCP tutorial, and Java tutorial.