E-commerce System – Spring Boot Sample

This is an advanced, educational Spring Boot project modeling a simple e-commerce/loan system. It showcases best practices in JPA, validation, REST design, caching, async processing, and messaging, with detailed commentary to accelerate understanding.

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TL;DR

• Start deps: docker-compose -f amit/mysqldockercompose/docker-compose.yaml up, -f amit/redis_docker_compose/docker-compose.yaml up, -f amit/kafka_docker_compose/docker-compose.yaml up
• Run app: mvnw.cmd spring-boot:run
• Try: GET http://localhost:8080/api/products/pagelist
• Send Kafka msg: POST /api/products/send-test-message with { "message": "hello" }
• Logs: ./logs/app.log and console

Project Structure

src/
└─ main/
   ├─ java/com/example/ecommercesystem/
   │  ├─ config/       ← Redis, Kafka, Security configuration
   │  ├─ controller/   ← REST endpoints (Products, Loans)
   │  ├─ service/      ← Business logic, caching, async processing
   │  ├─ repository/   ← Spring Data JPA interfaces
   │  ├─ model/        ← Entities with rich validation and mapping
   │  └─ kafka/        ← Test producer/consumer services
   └─ resources/
      ├─ application.properties      ← base config (DB, Redis, Kafka, logging)
      ├─ application-dev.properties  ← dev overrides & verbose logging
      └─ log4j.properties, reload4j.properties

amit/
├─ mysqldockercompose/      ← MySQL docker-compose + persisted volume
├─ redis_docker_compose/    ← Redis docker-compose + persisted volume
└─ kafka_docker_compose/    ← Kafka docker-compose + persisted volume

src/test/java/              ← JUnit 5 tests (model + context)

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Getting Started

Prerequisites

• JDK 8+ (JDK 11 recommended)
• Maven (or use wrapper mvnw.cmd on Windows)
• Docker Desktop (for MySQL, Redis, Kafka)

Start Local Dependencies (Docker)

Run from repo root in separate terminals:

• MySQL: docker-compose -f amit/mysqldockercompose/docker-compose.yaml up
• Redis: docker-compose -f amit/redis_docker_compose/docker-compose.yaml up
• Kafka: docker-compose -f amit/kafka_docker_compose/docker-compose.yaml up

Build & Run

mvnw.cmd clean install
mvnw.cmd spring-boot:run

App starts at http://localhost:8080

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Feature Highlights

Entity Modeling

• Product, Category, Loan with extensive validation annotations (@NotBlank, @Size, @Email, @Future, @PastOrPresent, numeric bounds)
• Relationship mapping with clear guidance on cascade and fetch strategies
• JSON serialization control to avoid cycles (@JsonManagedReference, @JsonIgnore)

Repository Layer

• Spring Data JPA derived queries and custom JPQL with @Query
• Pagination and sorting via Pageable

Service Layer, Caching, and Async

• Redis-backed Spring Cache (@Cacheable, @CachePut, @CacheEvict) for product list and product-by-id
• ExecutorService + Future + CompletableFuture patterns for concurrent processing

REST & Validation

• Product and Loan controllers with @Valid at boundaries
• Centralized error handling via @ControllerAdvice with consistent response shape

Messaging (Kafka)

• Simple producer/consumer wired with String serdes (test_topic)
• Test endpoint to publish messages

Observability

• Spring Boot Actuator endpoints exposed for development

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cURL Cheatsheet

• List products: curl http://localhost:8080/api/products
• Paged products: curl "http://localhost:8080/api/products/pagelist?page=0&size=12"
• Get product by id: curl http://localhost:8080/api/products/1
• Search products: curl "http://localhost:8080/api/products/search?name=Laptop&description=gaming"
• Create product: curl -X POST http://localhost:8080/api/products -H "Content-Type: application/json" -d '{"name":"Laptop","description":"Gaming","price":1299.99,"contactEmail":"support@example.com","quantityAvailable":10}'
• Fire-and-forget processing: curl -X POST http://localhost:8080/api/products/process
• Futures result: curl -X POST http://localhost:8080/api/products/process-async-with-futures
• CompletableFuture result: curl -X POST http://localhost:8080/api/products/process-async-with-cf
• Kafka test: curl -X POST http://localhost:8080/api/products/send-test-message -H "Content-Type: application/json" -d '{"message":"hello"}'

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API Endpoints (Selected)

• Products
  • GET /api/products – list all (cached)
  • GET /api/products/pagelist?page=&size= – paged listing
  • GET /api/products/{id} – get by id
  • GET /api/products/search?name=...&description=...
  • POST /api/products – create (validated)
  • Async demos: POST /api/products/process, /process-async-with-futures, /process-async-with-cf
  • Kafka test: POST /api/products/send-test-message with { "message": "hello" }
• Loans
  • GET /loans | GET /loans/{id} | POST /loans | PUT /loans/{id} | DELETE /loans/{id}
• Actuator
  • GET /actuator

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Configuration

• MySQL: jdbc:mysql://0.0.0.0:3306/loan_management (mysqluser/mysqlpass)
• Redis: localhost:6379
• Kafka bootstrap: localhost:9092
• Active profile: dev

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Configuration Deep Dive

• Profiles
  • Active: dev (see application-dev.properties)
  • Override via env: SPRING_PROFILES_ACTIVE=dev
• Database (MySQL)
  • URL: spring.datasource.url=jdbc:mysql://0.0.0.0:3306/loan_management
  • User/Pass: spring.datasource.username=mysqluser, spring.datasource.password=mysqlpass
  • DDL: spring.jpa.hibernate.ddl-auto=update (use validate/migrations for prod)
• Redis Cache
  • Host/Port: spring.redis.host=localhost, spring.redis.port=6379
  • Cache type: spring.cache.type=redis, TTL: spring.cache.redis.time-to-live=600000
• Kafka
  • spring.kafka.bootstrap-servers=localhost:9092, consumer group myGroup
• Logging
  • Root level: INFO; file output to ./logs/app.log

Environment overrides (PowerShell):

$env:SPRING_PROFILES_ACTIVE="dev"
$env:SPRING_DATASOURCE_URL="jdbc:mysql://localhost:3306/loan_management"
$env:SPRING_DATASOURCE_USERNAME="mysqluser"
$env:SPRING_DATASOURCE_PASSWORD="mysqlpass"
mvnw.cmd spring-boot:run

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Database Notes

• Entities: Product, Category, Loan
• Relationships: Product → Category many-to-one; Category.products one-to-many with orphan removal
• Batch inserts: GenerationType.IDENTITY impacts JDBC batching; prefer sequences for bulk loads
• Suggested indexes: product(name), product(price), category(name)

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Caching Details

• Cache names: products (list), product (by id)
• Keys: product::<id>, products::SimpleKey []
• Invalidation: saveProduct evicts all products and updates product::<id>
• Serialization: GenericJackson2JsonRedisSerializer

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Kafka How-To

• Start broker via docker-compose (topic auto-create enabled)
• Produce via API: POST /api/products/send-test-message with { "message": "hi" }
• Observe logs: consumer prints Received test_topic Message: ... in console

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Testing

• JUnit 5 tests under src/test/java (model tests, context loads)

Handy commands

• Run all tests: mvnw.cmd test
• Skip tests on build: mvnw.cmd -DskipTests clean install
• Single test: mvnw.cmd -Dtest=ProductTest test

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Why This Project Exists

To serve as a live textbook for Spring Boot, JPA, caching, async, and messaging—bridging theory and production-grade code in one resource. Useful for:

• Self-learners and interview prep
• Bootcamp/instructor demos
• Team onboarding and mentorship

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Error Model & Validation

• Validation failures (HTTP 400):

{
  "error": "validation_failed",
  "fields": {
    "name": "Product name cannot be blank"
  }
}

• Not found (HTTP 404): JSON with timestamp, message, details

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Pagination & Sorting

• Default page size: 12; default sort: id,asc
• Request format: GET /api/products/pagelist?page=0&size=12&sort=id,asc
• Response provides content, totalElements, totalPages, number, etc.

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Roadmap / TODO (Inline)

Implemented

• Redis cache integration for products (Spring Cache with Redis)
• Logging setup (SLF4J + log4j/reload4j), file + console
• JUnit 5 tests scaffold (model + context)
• Kafka basics (producer/consumer) and test endpoint
• Product pagination endpoint (/api/products/pagelist)
• Async processing (ExecutorService, Futures, CompletableFuture)
• MySQL via Spring Data JPA (entities, repositories)
• Actuator endpoints enabled in dev
• Dev profile and overrides
• Docker Compose for MySQL, Redis, Kafka

Planned

• Fix/verify serialization infinite loops in bidirectional entities
• Kafka concurrent processing patterns and tuning
• Connection pool sizing and thread configuration
• Custom decorator example
• Refine profile-specific configuration beyond dev
• WebSocket sample implementation
• Transactional boundaries and DB-level locking demos
• MongoDB setup and integration
• Harden Spring Security (currently permissive for development)

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Contributions & License

Contributions that enhance educational value are welcome.

License: MIT (if a LICENSE file is present in the repo).

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Happy learning—and may this be the forge of your architectural mastery.