multiple datasources using Spring Boot

This Spring Boot application demonstrates how to work with multiple datasources and implement efficient parallel data fetching.

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Features

• Multiple database connections (PostgreSQL and MySQL)

• Parallel data fetching using CompletableFuture

• Database migrations using both Liquibase and Flyway

• Exception handling with Problem Details

• Virtual Threads support

• Swagger API documentation

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Architecture

Database Setup

• PostgreSQL Database: Stores member information

  • Managed by Liquibase migrations

  • Uses sequence-based ID generation

• MySQL Database: Stores cardholder information

  • Managed by Flyway migrations

  • Uses identity-based ID generation

Key Components

• DetailsService: Implements parallel data fetching

  • Uses CompletableFuture for asynchronous operations

  • Implements timeout handling (5 seconds)

  • Provides comprehensive error handling

• Data Models:

  • Member: Core member information (PostgreSQL)

  • CardHolder: Card-related information (MySQL)

• Exception Handling:

  • CustomServiceException: For service-layer errors

  • MemberNotFoundException: For missing member scenarios

  • Problem Details support for standardized error responses

Configuration

PostgreSQL Configuration

spring.datasource.url=jdbc:postgresql://localhost:5432/memberdb
spring.datasource.username=postgres
spring.datasource.password=postgres

MySQL Configuration

app.datasource.cardholder.url=jdbc:mysql://localhost:3306/cardholderdb
app.datasource.cardholder.username=user
app.datasource.cardholder.password=password

Getting Started

1. Start PostgreSQL and MySQL databases

2. Configure database connections in application.properties

3. Run the application: The databases will be automatically initialized

4. Access Swagger UI: http://localhost:8080/swagger-ui.html

Implementation Notes

• Database migrations run automatically on startup

• Data bootstrapping occurs via ApplicationReadyEvent

• Parallel data fetching implemented using Spring's @Qualifier("applicationTaskExecutor")

• Virtual Threads enabled for improved scalability

• HikariCP connection pooling with optimized settings

• Automatic commit disabled for better transaction control

API Endpoints

• GET /api/details/{memberId}: Fetches member details from both databases in parallel

  • Returns combined information from both datasource's

  • Implements timeout handling (5 seconds)

  • Returns standardized error responses using Problem Details

Testing

• Integration tests demonstrate concurrent request handling

• MockMvcTester used for API testing

• Testcontainers with parallel startup for database testing