Library Management System | Android App

CoolLib — Native Android Client

Jetpack Compose Kotlin MVVM Hilt DI

A high-performance library management mobile application featuring a "Book-Style" custom design system. Built with Clean Architecture, it provides an offline-first experience with real-time synchronization to the Spring backend.

Source Code

Architectural Philosophy

CoolLib Android is engineered using Modern Android Development (MAD) practices. By implementing a reactive data pipeline and strict layer separation, the app ensures a fluid user experience even under complex data states and varying network conditions.

Key Technical Wins

Clean Architecture

Implemented strict MVVM with isolated Data, Domain, and UI layers using Kotlin-First principles for maximum maintainability.

Performance Tuning

Reduced data load times by 60% via Coroutines (async/awaitAll) for concurrent repository-level data mapping and transformation.

Dependency Injection

Engineered a robust DI graph with Hilt, utilizing custom Qualifiers (@IoDispatcher) for granular threading control.

Reactive Pipeline

Built a real-time data flow using StateFlow/SharedFlow integrated with Room for a reliable "Offline-First" experience.

Data Flow Architecture

Android App Architecture

flowchart LR subgraph DI ["`**Hilt Dependency Injection**`"] Hilt{{Hilt Container}} end subgraph Data ["`**Data Layer**`"] direction TB Room[(Room Database)] DAO(Data Access Objects) Impl(RepositoryImpl) end subgraph Domain ["`**Domain Layer**`"] direction TB RepoI(interface Repository) UC(UseCases / Interactors) end subgraph Presentation ["`**UI Layer**`"] direction TB VM(ViewModel) UIState([UiState]) Compose(Jetpack Compose) end Room <--> DAO Impl --> DAO Impl -.->|Implements| RepoI UC --> RepoI VM --> UC VM -- "Exposes" --> UIState UIState -- "Renders" --> Compose Compose -- "User Action" --> VM Hilt -.->|Inject| DAO Hilt -.->|Binds interface to| Impl Hilt -.->|Inject| UC Hilt -.->|Inject| VM %% ========================= %% STYLE SYSTEM (Light Theme) %% ========================= style Hilt fill:#0284c7,stroke:#0369a1,stroke-width:2px,color:#ffffff style Room fill:#334155,stroke:#1e293b,stroke-width:2px,color:#ffffff style DAO fill:#475569,stroke:#334155,stroke-width:2px,color:#ffffff style Impl fill:#64748b,stroke:#475569,stroke-width:2px,color:#ffffff style RepoI fill:#0d9488,stroke:#0f766e,stroke-width:2px,color:#ffffff style UC fill:#14b8a6,stroke:#0d9488,stroke-width:2px,color:#ffffff style VM fill:#16a34a,stroke:#15803d,stroke-width:2px,color:#ffffff style UIState fill:#bbf7d0,stroke:#16a34a,stroke-width:2px,color:#14532d style Compose fill:#f0fdf4,stroke:#16a34a,stroke-width:2px,color:#166534 style DI fill:none,stroke:#0284c7,stroke-dasharray: 5 5 style Data fill:none,stroke:#475569,stroke-dasharray: 5 5 style Domain fill:none,stroke:#0d9488,stroke-dasharray: 5 5 style Presentation fill:none,stroke:#16a34a,stroke-dasharray: 5 5 linkStyle default stroke:#64748b,stroke-width:1.5px

● Strict Unidirectional Data Flow (UDF) powered by Kotlin StateFlow and Hilt DI.

Single Source of Truth (SSOT)

Data Fetching Logic (Search vs Detail)

graph LR %% ==================== 搜索场景 ==================== subgraph Search_Scenario ["`**BookScreen - Search (Remote Only)**`"] SUI(Search UI) SVM(SearchViewModel) SRepo(BookRepository) SAPI[Retrofit API] SUI -->|1. Type Query| SVM SVM -->|2. Call| SRepo SRepo -->|3. HTTP GET| SAPI SAPI -.->|4. DTO List| SRepo SRepo -.->|5. Domain Models| SVM SVM -.->|6. Update StateFlow| SUI end %% 强制垂直隔离线 Search_Scenario --- Detail_Scenario linkStyle 0 stroke:transparent,stroke-width:0px; %% ==================== 详情页场景 ==================== subgraph Detail_Scenario ["`**BookDetailScreen - Cache First**`"] DUI(Detail UI) DVM(DetailViewModel) DRepo(BookRepositoryImpl) DB[(Room DB)] DAPI[Retrofit API] %% UI 到 Repo 的请求流 DUI -->|1. Request ID| DVM DVM -->|2. Fetch| DRepo %% 缓存优先策略 (Cache-First) DRepo -->|3. Check Cache| DB DB -.->|4a. Found: Return Data| DRepo %% 缓存未命中流 (Cache Miss) DRepo -->|4b. Miss: Fetch Remote| DAPI DAPI -->|5. Save Network DTO| DB DB -.->|6. Emit Updated Data| DRepo %% 统一返回 UI 流 DRepo -.->|7. Domain Model| DVM DVM -.->|8. BookUiState| DUI end %% ==================== 现代 Slate & Teal 样式 ==================== %% 节点样式 style SUI fill:#f0fdf4,stroke:#16a34a,stroke-width:2px,color:#166534 style DUI fill:#f0fdf4,stroke:#16a34a,stroke-width:2px,color:#166534 style SVM fill:#16a34a,stroke:#15803d,stroke-width:2px,color:#ffffff style DVM fill:#16a34a,stroke:#15803d,stroke-width:2px,color:#ffffff style SRepo fill:#0d9488,stroke:#0f766e,stroke-width:2px,color:#ffffff style DRepo fill:#0d9488,stroke:#0f766e,stroke-width:2px,color:#ffffff style SAPI fill:#475569,stroke:#334155,stroke-width:2px,color:#ffffff style DAPI fill:#475569,stroke:#334155,stroke-width:2px,color:#ffffff style DB fill:#334155,stroke:#1e293b,stroke-width:2px,color:#ffffff %% 容器样式 style Search_Scenario fill:none,stroke:#64748b,stroke-width:1.5px,stroke-dasharray: 3 3 style Detail_Scenario fill:none,stroke:#64748b,stroke-width:1.5px,stroke-dasharray: 3 3 %% 全局线条 linkStyle default stroke:#64748b,stroke-width:1.5px

*Search provides real-time results, while Details use an on-demand caching strategy.*

Tech Stack

UI Framework: Jetpack Compose, Material 3, Coil, Compose Navigation
Logic & Concurrency: MVVM, Clean Architecture, Coroutines, Kotlin Flow, Hilt (DI)
Data Persistence: Retrofit, Moshi, Room (Local DB), DataStore

Core Features

Loan Tracking

Smart Insights

Intelligent Search

Book-Style UI

Method	Endpoint	Business Logic & Description
POST	`/api/loan/checkout`	Initiate Loan: Validates scanned ISBN against library inventory. Checks user borrowing limits and calculates the initial 14-day due date.
GET	`/api/loan/active`	Real-time Status: Returns a list of current holdings. Backend performs dynamic calculations for "Days Remaining" and marks items as `OVERDUE` if past deadline.
PATCH	`/api/loan/extend/{id}`	Renewal Request: Extends due date by 7 days. Conflict Check: Request is rejected if the book has an active Reservation by another user. Policy-Driven
GET	`/api/loan/history`	Audit Trail: Accesses archived loan records. Useful for Personal Analytics and verifying returned dates to resolve disputes.
PUT	`/api/loan/reminders`	Fulfillment Logic: Syncs device FCM Token to backend. Triggers automated push alerts 2 days before the due date to minimize late fees. Automation

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CoolLib — Native Android Client

Architectural Philosophy

Key Technical Wins

Clean Architecture

Performance Tuning

Dependency Injection

Reactive Pipeline

Data Flow Architecture

Single Source of Truth (SSOT)

Tech Stack

Core Features

Local-First Persistence

Asynchronous Orchestration

Domain-Centric Logic

Declarative Composition

Search Engine Architecture

Sub-ms Room FTS5

Debounced Stream Processing

"Paper-like" Tactile UX

Where Paper Meets Pixels

Visual Storytelling

Thoughtful Curation

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