> For the complete documentation index, see [llms.txt](https://rajadilipkolli.gitbook.io/my-spring-boot-experiments/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://rajadilipkolli.gitbook.io/my-spring-boot-experiments/jpa/boot-data-multipledatasources.md).

# multiple datasources using Spring Boot

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

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

### MySQL Configuration

```properties
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


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://rajadilipkolli.gitbook.io/my-spring-boot-experiments/jpa/boot-data-multipledatasources.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.