Configuring Multiple Data Sources in Spring Boot

To support heterogeneous database access—such as reading from both MySQL and PostgreSQL—Spring Boot applications can be configured with multiple data sources using dynamic routing.

Dependency Setup

Add the following dependencies to pom.xml:

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>
<dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <scope>runtime</scope>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>dynamic-datasource-spring-boot-starter</artifactId>
    <version>3.6.1</version>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.2</version>
</dependency>
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.3.1</version>
</dependency>

DataSource Configuration

Define two named data sources in application.yml:

spring:
  datasource:
    dynamic:
      primary: postgresql
      strict: false
      datasource:
        postgresql:
          driver-class-name: org.postgresql.Driver
          url: jdbc:postgresql://localhost:5432/myapp_pg
          username: pg_user
          password: pg_pass
        mysql:
          driver-class-name: com.mysql.cj.jdbc.Driver
          url: jdbc:mysql://localhost:3306/myapp_mysql?useSSL=false&serverTimezone=UTC
          username: mysql_user
          password: mysql_pass

The primary key specifies the default data source used when no explicit routing is declared.

Mapper Organization and Routing

Group mapper interfaces by target database. For example:

• src/main/java/com/example/mapper/postgres/ contains interfaces for PostgreSQL.
• src/main/java/com/example/mapper/mysql/ contains interfaces for MySQL.

Corresponding XML maping files should follow the same structure under src/main/resources/mapper/.

Configure MyBatis Plus to scan mappers correctly:

mybatis-plus:
  mapper-locations: classpath:mapper/**/*Mapper.xml

Data Source Selection at Runtime

Use the @DS annotation on mapper interfaces or methods to route queries:

@Mapper
@DS("postgresql")
public interface UserPostgreSqlMapper {
    List<User> findAll();
}

@Mapper
@DS("mysql")
public interface OrderMySqlMapper {
    List<Order> findRecent();
}

Omitting @DS defaults to the primary data source (postgresql, per configuration). Explicit annotation improves clarity and maintainability.

Optional: Custom DataSource Resolver

For programmatic control, inject DynamicRoutingDataSource and use DsContextHolder.set("mysql") before operations—though declarative @DS is preferred for most cases.