Payment Processing Demo — Java 17

A mock credit card payment processing application built with Spring Boot 3.x (Java 17) and React.

Quick Start

cd payment-app-java17
mvn spring-boot:run

Then open http://localhost:8080 in your browser.

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What Changed from Java 11

Area	Java 11 (payment-app)	Java 17 (payment-app-java17)
Spring Boot	2.7.18	3.2.5
Java version	11	17
javax.* imports	javax.persistence.*, javax.validation.*	jakarta.persistence.*, jakarta.validation.*
AuthorizeRequest	Verbose POJO with getters/setters	Record
CaptureRequest	Verbose POJO with getter/setter	Record
RefundRequest	Verbose POJO with getter/setter	Record
PaymentResponse	POJO + Builder pattern	Record (canonical constructor)
PaymentService.getHistory()	Collectors.toList()	Stream.toList() (unmodifiable)
Error messages	String concatenation	Text blocks with .formatted()
Exception handling	Explicit cast after instanceof	Pattern matching instanceof
Prometheus property	management.metrics.export.prometheus.enabled	management.prometheus.metrics.export.enabled
Dockerfile build stage	maven:3.8.8-eclipse-temurin-11	maven:3.9.6-eclipse-temurin-17
Dockerfile runtime	gcr.io/distroless/java11-debian12:nonroot	gcr.io/distroless/java17-debian12:nonroot

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API Endpoints

Method	Path	Description
POST	/api/payments/authorize	Authorize a card transaction
POST	/api/payments/capture	Capture an authorized transaction
POST	/api/payments/refund	Refund a captured transaction
GET	/api/payments/{id}	Get transaction by ID
GET	/api/payments/history	List recent 20 transactions
POST	/admin/cache/clear	Clear the local Caffeine cache
GET	/actuator/health	Readiness / health probe
GET	/actuator/prometheus	Prometheus metrics

Authorize a Payment

curl -X POST http://localhost:8080/api/payments/authorize \
  -H "Content-Type: application/json" \
  -d '{
    "cardNumber": "4263970000005262",
    "expiryMonth": "12",
    "expiryYear": "26",
    "cvv": "123",
    "amount": 99.99,
    "currency": "USD"
  }'

Capture a Transaction

curl -X POST http://localhost:8080/api/payments/capture \
  -H "Content-Type: application/json" \
  -d '{"transactionId": "<id from authorize response>"}'

Refund a Transaction

curl -X POST http://localhost:8080/api/payments/refund \
  -H "Content-Type: application/json" \
  -d '{"transactionId": "<id from capture response>"}'

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Test Card Numbers

Network	Card Number
Visa	4263970000005262
MasterCard	5425230000004415
Amex	374101000000608

Use any future expiry date (e.g., 12/26) and any 3–4 digit CVV.

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Simulated Behavior

• Processing delay: 200–500 ms per request
• Random decline rate: ~10% of transactions
• Response codes:
  • 00 — Approved
  • 51 — Insufficient Funds
  • 05 — Do Not Honor
  • 54 — Expired Card

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Transaction Status Flow

AUTHORIZED → CAPTURED → REFUNDED
     └──────→ DECLINED (terminal)

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Docker

Build

docker build -t payment-app-java17 .

Run

docker run -p 8080:8080 payment-app-java17

The image uses a distroless base (gcr.io/distroless/java17-debian12:nonroot) and runs as a non-root user (uid 65532).

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Tech Stack

Layer	Technology
Backend	Java 17, Spring Boot 3.2.5
Database	H2 (in-memory)
Cache	Caffeine (local, 10 min TTL)
Metrics	Micrometer + Prometheus
Frontend	React 18 (CDN, no build step)
Container	Distroless Java 17, non-root user

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H2 Console

Available at http://localhost:8080/h2-console

• JDBC URL: jdbc:h2:mem:paymentdb
• Username: sa
• Password: (empty)

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Java 17 Features Applied

Records (AuthorizeRequest, CaptureRequest, RefundRequest, PaymentResponse)

Records auto-generate the canonical constructor, accessors, equals(), hashCode(), and toString(). Jackson 2.15 (Spring Boot 3.x) deserializes records via the canonical constructor. Hibernate Validator 8.x validates annotations on record components.

Text Blocks (PaymentService)

Error messages in capture() and refund() use text blocks with .formatted() for cleaner multi-line string templates.

Pattern Matching instanceof (PaymentController)

Exception handlers use if (e instanceof IllegalStateException ise) — eliminates the redundant explicit cast.

Stream.toList() (PaymentService.getHistory())

Replaces Collectors.toList() with the Java 16+ Stream.toList(), which returns an unmodifiable list — safer for a read-only history endpoint.

jakarta.* Namespace

All javax.persistence.* and javax.validation.* imports replaced with jakarta.* as required by Jakarta EE 9+ / Spring Boot 3.x.