How do you create a Spring Boot application that connects to multiple data sources?

Table of Contents

• Introduction
• 1. Defining Multiple Data Sources in Spring Boot
  • Step 1: Add Dependencies
• 2. Configuring Multiple Data Sources
  • Step 2: Configure Properties for Data Sources
  • Step 3: Create DataSource Configuration Classes
    • Configuration for the First Data Source (MySQL):
    • Configuration for the Second Data Source (PostgreSQL):
• 3. Creating Repositories for Each Data Source
  • • MySQL Repository Example:
    • PostgreSQL Repository Example:
• 4. Using the Data Sources in Your Application
• Conclusion

Introduction

In modern applications, it’s common to work with multiple databases or data sources. For example, you might need one data source for transactional data and another for analytical queries, or you may want to separate data storage between different services. Spring Boot provides an easy way to configure multiple data sources, allowing you to seamlessly connect and interact with more than one database in the same application.

In this guide, we’ll explore how to set up and configure multiple data sources in a Spring Boot application using Spring Data JPA. We will cover how to configure two different data sources, create separate DataSource beans, and define EntityManagerFactory for each source.

1. Defining Multiple Data Sources in Spring Boot

To connect to multiple data sources in Spring Boot, you'll need to:

• Configure two different DataSource beans.
• Configure two separate EntityManagerFactory beans for each database.
• Configure separate transaction managers for each data source.

Step 1: Add Dependencies

First, add the necessary dependencies for Spring Data JPA and your database connectors in the pom.xml file. Here's an example for connecting to two different databases (e.g., MySQL and PostgreSQL):

2. Configuring Multiple Data Sources

Step 2: Configure Properties for Data Sources

In your application.properties or application.yml file, define the connection properties for both databases. For instance:

Here:

• **spring.datasource** refers to the first data source (e.g., MySQL).
• **spring.datasource.secondary** is used to configure the second data source (e.g., PostgreSQL).

Step 3: Create DataSource Configuration Classes

To set up multiple data sources, you need to create two separate configuration classes that define beans for each data source, EntityManagerFactory, and TransactionManager.

Configuration for the First Data Source (MySQL):

Configuration for the Second Data Source (PostgreSQL):

3. Creating Repositories for Each Data Source

Each data source requires its own set of repositories, so make sure you organize them into different packages based on the database they belong to.

MySQL Repository Example:

PostgreSQL Repository Example:

4. Using the Data Sources in Your Application

Now that you’ve configured the data sources, you can inject the appropriate repository into your services or controllers as needed.

Conclusion

Configuring multiple data sources in a Spring Boot application is essential when dealing with multiple databases. The key steps include:

1. Configuring DataSource Beans: Define separate DataSource beans for each database.
2. Setting Up Entity Manager and Transaction Managers: Define EntityManagerFactory and PlatformTransactionManager beans for each data source.
3. Creating Repositories: Define separate repositories for each data source.
4. Using in Services: Inject and use the repositories in services as required.

By following this approach, you can efficiently manage and interact with multiple data sources in a single Spring Boot application, allowing your application to scale and integrate with diverse databases.