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Multiple Datasource's with Parallel Data Fetching

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

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

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