Bind properties in application.yml not working

In my SpringBoot project I have application.yml file in src/main/resources/:

server:
  port: 8080

spring:
  datasource:
    driver-class-name: org.sqlite.JDBC
    ...

I want to bind the properties defined above to a Java class:

@Configuration
@ConfigurationProperties(prefix = "spring.datasource")
public class DBConfig {

    // I wished spring-boot could automatically bind it with 'driver-class-name' in application.yml
    private String driverClassName;
    ...

    @Bean
    public DataSource dataSource() {
        final DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(driverClassName);
        ...
        return dataSource;
    }
}

I have the annotation @Configuration and @ConfigurationProperties(prefix = "spring.datasource"). I also have specified the correct prefix. But when I run my application I get an error:

> Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [com/my/webapp/config/DBConfig.class]: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception with message: Property 'driverClassName' must not be empty

The error tells driverClassName is an empty string, so the binding doesn't work. What am I missing? I am using an SQLite database which is not as well supported as MySQL, MariaDB, etc. in SpringBoot. So I provide a datasource bean class to bind database configurations in application.yml to the manually created bean class. Is it unnecessary?

The usual way for configuration properties is to keep them in the separate class and activate them using @EnableConfigurationProperties. You can read this article. And you can try something as follows:

@Configuration
@EnableConfigurationProperties(MyConfigurationProperties.class)
public class DBConfig {

    @Autowired
    private MyConfigurationProperties props;

    @Bean
    public DataSource dataSource() {
        final DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(props.getDriverClassName());
        // ...
        return dataSource;
    }
}

And your properties class will look like this:

@ConfigurationProperties(prefix = "spring.datasource")
public class MyConfigurationProperties {
    
    private String driverClassName;

    // getters ans setters are here
}

But I'm not sure if this is the best solution, because Spring already has its own configuration properties class that binds to the prefix spring.datasource.

And the second option for you is to use the Spring configuration properties:

import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
// ...

@Configuration
@EnableConfigurationProperties(DataSourceProperties.class)
public class DBConfig {

    @Autowired
    private DataSourceProperties props;

    @Bean
    public DataSource dataSource() {
        final DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(props.getDriverClassName());
        // ...
        return dataSource;
    }
}

You only need to add setters for feilds in your DBConfig class and it will work.