M04 Q20 How are DataSource and JdbcTemplate autoconfigured?

DataSource and JdbcTemplate are configured by Auto Configuration Classes defined in spring-boot-autoconfigure module.

DataSource is configured by DataSourceAutoConfiguration, JdbcTemplate is configured by JdbcTemplateAutoConfiguration. DataSourceAutoConfiguration requires some properties to be defined, example below shows MySQL configuration:

spring.datasource.url=jdbc:mysql://localhost:3306/spring-tutorial
spring.datasource.username=spring-tutorial
spring.datasource.password=spring-tutorial

Above properties will be injected into DataSourceProperties by the prefix spring.datasource and used by DataSourceAutoConfiguration.

After having Auto Configuration enabled by default in Spring Boot, configured properties and Database Connector on your classpath, you can just use @Autowire to inject DataSource or JdbcTemplate.