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Java Spring
Messenger

Educational backend project implementing a messaging system with Spring Boot. REST API, user management, message threading and standard Spring layered architecture.

JavaSpring Boot Spring SecuritySpring Data JPA REST APIPostgreSQL
Overview

What it does

A backend-only messaging service built to explore Spring Boot architecture. Covers the full request lifecycle from REST controller through service layer to JPA repository, with Spring Security for auth.

Designed as a learning project, the codebase demonstrates idiomatic Spring patterns: dependency injection, transaction management, DTO mapping and integration testing with MockMvc.

Features

Key capabilities

01
User management
Registration, login, profile CRUD. Password hashing with BCrypt. JWT-based stateless authentication.
02
Messaging logic
Send and receive messages. Conversation threading by participants. Paginated message history.
03
REST API
Standard HTTP methods and status codes. JSON request/response. Input validation with Spring Validator.
04
Spring architecture
Clean Controller → Service → Repository layering. Spring Data JPA with H2 (dev) and PostgreSQL (prod).
Architecture

Project structure

tree
src/main/java/
└── messenger/
    ├── controller/
    │   ├── AuthController.java      # /api/auth/*
    │   ├── UserController.java      # /api/users/*
    │   └── MessageController.java   # /api/messages/*
    ├── service/
    │   ├── AuthService.java
    │   ├── UserService.java
    │   └── MessageService.java
    ├── repository/
    │   ├── UserRepository.java
    │   └── MessageRepository.java
    ├── model/
    │   ├── User.java
    │   └── Message.java
    ├── dto/                         # Request/response DTOs
    ├── security/                    # JWT filter, Spring Security config
    └── config/
API

REST endpoints

http
# Auth
POST  /api/auth/register   # { username, email, password }
POST  /api/auth/login      # { email, password } → JWT

# Users
GET   /api/users/me        # current user profile
PUT   /api/users/me        # update profile

# Messages
GET   /api/messages        # ?with=userId&page=0&size=20
POST  /api/messages        # { recipientId, content }
GET   /api/conversations   # list all conversations
Installation

Running locally

bash
# Requires Java 17+ and Maven
mvn spring-boot:run

# Runs on http://localhost:8080
# H2 console: http://localhost:8080/h2-console