Configuring a DataSource Programmatically in Spring Boot

Spring Boot uses an opinionated algorithm to scan for and configure a DataSource. This allows us to easily get a fully-configured DataSource implementation by default.

In addition, Spring Boot automatically configures a lightning-fast connection pool, either HikariCP, Apache Tomcat, or Commons DBCP, in that order, depending on which are on the classpath.

While Spring Boot’s automatic DataSource configuration works very well in most cases, sometimes we’ll need a higher level of control, so we’ll have to set up our own DataSource implementation, hence skipping the automatic configuration process.

In this tutorial, we’ll learn how to configure a DataSource programmatically in Spring Boot.

Further reading:

Spring JPA – Multiple Databases

How to set up Spring Data JPA to work with multiple, separate databases.

Configuring Separate Spring DataSource for Tests

A quick, practical tutorial on how to configure a separate data source for testing in a Spring application.

2. The Maven Dependencies

Creating a DataSource implementation programmatically is straightforward overall.

To learn how to accomplish this, we’ll implement a simple repository layer, which will perform CRUD operations on some JPA entities.

Let’s take a look at our demo project’s dependencies:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <version>2.4.1</version>
    <scope>runtime</scope>
</dependency>

As shown above, we’ll use an in-memory H2 database instance to exercise the repository layer. In doing so, we’ll be able to test our programmatically-configured DataSource, without the cost of performing expensive database operations.

In addition, let’s make sure to check the latest version of spring-boot-starter-data-jpa on Maven Central.

3. Configuring a DataSource Programmatically

Now, if we stick with Spring Boot’s automatic DataSource configuration and run our project in its current state, it will work just as expected.

Spring Boot will do all the heavy infrastructure plumbing for us. This includes creating an H2 DataSource implementation, which will be automatically handled by HikariCP, Apache Tomcat, or Commons DBCP, and setting up an in-memory database instance.

Additionally, we won’t even need to create an application.properties file, as Spring Boot will provide some default database settings as well.

As we mentioned before, at times we’ll need a higher level of customization, so we’ll have to programmatically configure our own DataSource implementation.

The simplest way to accomplish this is by defining a DataSource factory method, and placing it within a class annotated with the @Configuration annotation:

@Configuration
public class DataSourceConfig {

    @Bean
    public DataSource getDataSource() {
        DataSourceBuilder dataSourceBuilder = DataSourceBuilder.create();
        dataSourceBuilder.driverClassName("org.h2.Driver");
        dataSourceBuilder.url("jdbc:h2:mem:test");
        dataSourceBuilder.username("SA");
        dataSourceBuilder.password("");
        return dataSourceBuilder.build();
    }
}

In this case, we used the convenient DataSourceBuilder class, a non-fluent version of Joshua Bloch’s builder pattern, to programmatically create our custom DataSource object.

6. Conclusion

In this article, we learned how to configure a DataSource implementation programmatically in Spring Boot.

As usual, all the code samples shown in this article are available over on GitHub.