Spring Boot · Java 17

Smart Wallet Application

A server-rendered wallet service: users hold multiple currency wallets, transfer funds to each other, and move between subscription tiers that are charged against a wallet balance.

Open the demo → No install, no database. Use demo accounts or register.

The demo

The console published alongside these docs is the application's own Thymeleaf markup and stylesheets, running against a seeded registry in your browser. There is no backend behind a static host, so the services in src/main/java/app are reproduced in JavaScript: the same arithmetic, the same failure reasons, the same order of checks.

What works

Sign in, register new accounts, transfer funds, top up a wallet, switch a wallet off, upgrade or downgrade a tier, edit your profile, and read the transaction and subscription history.

Seeded state

example with a 20.00 EUR main wallet on the DEFAULT tier. An admin account, admin, also exists to manage users and inspect roles.

Where state lives

In sessionStorage, so a reload keeps your balance and a new tab starts clean. Nothing is sent to a server.

Admin functions

Signing in as admin unlocks the Admin Users console in the sidebar, allowing user status toggling and role switching.

What it does

Wallets

Every registered user gets a main EUR wallet seeded with a starting balance. Deposits and withdrawals are recorded as transactions.

Transfers

A transfer is a withdrawal from the sender paired with a deposit to the recipient's first active wallet, inside one database transaction.

Subscriptions

Default, Premium and Ultimate tiers on a monthly or yearly period. Upgrading charges the chosen wallet and completes the previous subscription.

Notifications

Preferences are pushed to a separate notification service over an OpenFeign client. The call degrades to a logged warning when that service is down.

How a transfer flows

The controller resolves the authenticated user and hands it to WalletService.transfer, so the wallet id in the request is checked against its real owner before any balance moves. A withdrawal that fails ownership, an inactive wallet, or an insufficient balance is still persisted as a FAILED transaction with a failure reason, and the deposit never runs.

Running it locally

Requires JDK 17 and a MySQL instance on localhost:3306. The Maven wrapper is checked in, so no local Maven install is needed.

git clone https://github.com/PhoenixMaster123/smart-wallet-application.git
cd smart-wallet-application

./mvnw spring-boot:run

The app starts on http://localhost:8080 and seeds a default user from application.properties.

Profiles. dev is active by default and points at a local MySQL; the schema is created on first run. Deploy with --spring.profiles.active=prod and supply DB_URL, DB_USERNAME and DB_PASSWORD as environment variables.

Without a database

To boot against an in-memory H2 instead — this is exactly what CI does:

./mvnw clean package
java -jar target/smart-wallet-application-*.jar \
  --spring.datasource.url='jdbc:h2:mem:local;DB_CLOSE_DELAY=-1' \
  --spring.datasource.driverClassName=org.h2.Driver \
  --spring.datasource.username=sa \
  --spring.datasource.password= \
  --spring.jpa.hibernate.ddl-auto=create-drop

Routes

Route	Access	Purpose
GET `/`	Public	Landing page
GET `/login`	Public	Sign in
GET `/register`	Public	Create an account
GET `/home`	User	Dashboard: profile, main wallet, subscription
GET `/transfers`	User	Send funds to another user
GET `/transactions`	User	Transaction history
GET `/subscriptions`	User	Compare and buy a tier
GET `/subscriptions/history`	User	Past subscriptions
GET `/users/{id}/profile`	Self or admin	View and edit a profile
GET `/users`	Admin	User administration
GET `/reports`	Admin	Reporting

Architecture

Packages are organised by feature rather than by layer. Each of user, wallet, transaction and subscription owns its model, repository and service; web holds the controllers, DTOs and mappers that sit in front of them.

Persistence — Spring Data JPA over MySQL, schema managed by Hibernate.
Security — form login backed by UserDetailsService, with method-level @PreAuthorize guarding admin and per-user routes.
Views — Thymeleaf templates with the Spring Security dialect.
Events — a successful charge publishes an application event that the email and gift listeners handle asynchronously.
Service calls — OpenFeign clients for the notification service, written to tolerate it being unavailable.

Quality gates

CI runs on every push and pull request against master. All three steps must pass:

Step	Command
Checkstyle	`./mvnw checkstyle:check`
Build and test	`./mvnw clean verify`
Boot smoke test	Runs the packaged jar and waits for startup

The Checkstyle rules in config/checkstyle/checkstyle.xml are structural rather than cosmetic: imports, naming, braces and common correctness traps. Formatting an IDE already handles is left out, so the build fails only on things worth failing on.