Library Management System | Spring Backend

CoolLib — Distributed Library Core API

Spring Boot 3.4 PostgreSQL JWT Security Kotlin

A high-performance backend ecosystem engineered with Clean Architecture. It implements a strict separation between JPA Entities and DTOs, serving as the central orchestration hub for both Android (Kotlin) and iOS (SwiftUI) clients.

Source Code API Security

Project Overview

CoolLib Backend is a robust RESTful service built with Spring Boot 3.4 and Kotlin. Beyond standard CRUD operations, it manages complex business logic layers to ensure data consistency, security, and seamless synchronization across the mobile ecosystem.

Key Technical Wins

Layered Architecture

Strictly follows the Controller-Service-Repository pattern, ensuring complete decoupling between business logic and data access layers.

Secure Sessions

Integrated Spring Security with JWT (JSON Web Tokens) to provide a stateless authentication mechanism tailored for mobile clients.

Persistence Layer

Leverages PostgreSQL and Spring Data JPA, ensuring the atomicity of borrowing operations through @Transactional services.

Performance Optimization

Reduced network overhead via DTO Projections and optimized database indexing for high-speed book searches.

System Architecture

Architecture Design
graph TD A[CoolLib Android Jetpack Compose] B[CoolLib iOS SwiftUI + SwiftData] C{Restful API Spring MVC + JWT} D[Business Logic Book Service Layer] E[Data Access Spring Data JPA] F[(Persistence PostgreSQL)] A --> C B --> C C --> D D --> E E --> F style A fill:#3DDC84,stroke:#2eb26a,stroke-width:2px,color:#fff style B fill:#5AC8FA,stroke:#3fa7d6,stroke-width:2px,color:#fff style C fill:#6DB33F,stroke:#5a9234,stroke-width:2px,color:#fff style D fill:#4CAF50,stroke:#3d8b40,stroke-width:1px,color:#fff style E fill:#388E3C,stroke:#2e7031,stroke-width:1px,color:#fff style F fill:#336791,stroke:#264e6e,stroke-width:2px,color:#fff linkStyle default stroke:#8B4513,stroke-width:1.5px

*The backend follows a strict Stateless pattern.*

Authentication Flow

JWT Authentication Flow
sequenceDiagram autonumber participant Mobile as Mobile App participant Spring as Spring Boot API participant JWT as JwtProvider participant DB as PostgreSQL Note over Mobile, DB: 1. Login & Token Generation Mobile->>Spring: POST /api/auth/login Spring->>DB: Validate Credentials (BCrypt) DB-->>Spring: User Found & Matches Spring->>JWT: Generate Claims (UserID, Role) JWT-->>Spring: Return Signed JWT Spring-->>Mobile: 200 OK (Access Token) Note over Mobile, DB: 2. Authorized Request (Stateless) Mobile->>Spring: POST /api/loan (Header: Bearer <token>) Spring->>JWT: Validate Signature & Claims JWT-->>Spring: Token Valid (User: Ryan) Spring->>DB: Execute Loan Books Business DB-->>Spring: Return Data

*The security layer uses a OncePerRequestFilter to intercept and validate JWTs.*

Tech Stack

  • Core Framework: Spring Boot 3.4, Kotlin (JVM 17), Maven
  • Security: JWT, Spring Security, BCrypt Password Hashing
  • Data Management: PostgreSQL, Spring Data JPA, Hibernate ORM
  • Standards: RESTful API Design, Docker-Ready Deployment

Core Features

Advanced Search

Transaction Logic

Standardized Responses

Method Endpoint Description Auth
POST /api/v1/auth/login Verify credentials and issue a JWT Access Token.
POST /api/v1/borrow/scan Process borrowing via Barcode/ISBN scan. In Dev
GET /api/v1/stats/loans Fetch aggregate data of active loans and trends. Planned
GET /api/v1/users/profile Retrieve identity claims from the decrypted JWT payload.
GET /api/v1/auth/validate Check if the current token is expired or blacklisted.
Method Endpoint Description Auth
GET /api/v1/books/search Multi-criteria filtering by Title, Author, Publisher, and Year.
GET /api/v1/books/fuzzy Fuzzy search using Levenshtein Distance or partial matching logic. In Dev
GET /api/v1/books/recommend Content-based filtering using User Borrowing History. Planned
GET /api/v1/books/isbn/{isbn} Direct lookup via 10 or 13-digit International Standard Book Number.
Transaction Processing Pipeline
ACID SECURE
Identity Authorization
Extract userId & roles from JWT claims.
Concurrency Locking
Execute SELECT FOR UPDATE to prevent race conditions.
Business Validation
Verify stock availability and user borrow limits.
Atomic Commit
Persist LoanRecord & update Inventory.

Managed by Spring @Transactional logic.

book_dto_response.json
Large Content Handling

To optimize network bandwidth for mobile clients, long descriptions are truncated in search results and fully loaded only via the /details endpoint. 

{
  "status": "SUCCESS",
  "data": {
    "id": 262,
    "isbn": "9780099590088",
    "title": "Sapiens: A Brief History of Humankind",
    "author": "Yuval Noah Harari",
    "publisher": "Vintage",
    "year": 2011,
    "available": true,
    "description": "// [Omitted: 2,500+ characters of content] ..."
  },
  "_metadata": {
    "content_length": 2541,
    "truncated": true
  }
}
Performance Win: This partial loading strategy reduces the average payload size by 85% for book catalog browsing on mobile devices.

Mobile Connectivity

Both Android and iOS clients interact with this backend through standard REST endpoints.

Required Header: Authorization: Bearer <token>

Developed with passion by Ryan Su © 2026