LibFlow — Object-Oriented Library Management System in Java

An object-oriented library management application developed in Java. The system implements a rich domain model managing catalog inventory (Books, DVDs), user behavioral progression, dynamic loan validation rules, automated stock notifications, and binary state persistence.

Developed as part of the Object-Oriented Programming (Programação com Objetos — PO) course at Instituto Superior Técnico (IST), Universidade de Lisboa.

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Architectural Highlights & Design Patterns

The system adheres strictly to clean architecture and software engineering design patterns:

1. Strategy Pattern — Loan Rule Engine (RuleChecker)

Borrowing eligibility is evaluated through an extensible chain of independent rule strategies, preventing monolithic conditional branching:

• CheckActiveUser: Validates that the user is not suspended or penalized by unpaid overdue fines.
• CheckCategory: Enforces catalog restrictions (e.g. Reference works cannot be loaned).
• CheckInventory: Ensures available copies exist in the active collection.
• CheckPrice: Verifies that work value does not exceed borrowing limits for the user's current tier.
• CheckNumberRequisitions: Caps concurrent active loans based on user tier.
• CheckRequestTwice: Disallows concurrent duplicate loans of the same work by the same user.

2. State Pattern — User Behavioral Progression (UserBehavior)

User privileges dynamically evolve based on borrowing history and return punctuality:

• Normal: Base borrowing limits and standard return deadlines.
• Cumpridor (Compliant): Earned after consecutive on-time returns; grants extended loan durations and higher borrowing capacity.
• Faltoso (Delinquent): Triggered by overdue returns; imposes strict borrowing limits and requires consecutive timely returns to recover standing.

3. Observer Pattern — Availability Notifications (Notifiable)

An automated subscription mechanism for depleted inventory:

• Users subscribe to works that currently have zero available copies.
• When a copy is returned, state transitions trigger event notifications (DISPONIBILIDADE, REQUISICAO) queued directly into the subscriber's notification inbox.

4. Persistence via Serialization

• Full application state is saved and restored from binary snapshots using Java Object Serialization (LibraryManager), supporting seamless session restoration.

5. Command Pattern UI (bci.app & pt.tecnico.uilib)

• The application interface decouples UI controllers from core domain logic using hierarchical command menus, form prompts, and isolated exception handling.

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Project Structure

.
├── Makefile                # Build automation
├── LICENSE                 # MIT License
├── .gitignore              # Java build exclusions
├── README.md               # Project documentation
└── src/
    ├── bci/
    │   ├── app/            # Command menus, interaction handlers, and UI exceptions
    │   └── core/           # Domain entities, design patterns, and rule checkers
    └── pt/
        └── tecnico/uilib/  # Terminal dialog, form, and menu driver framework

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Requirements

• JDK 17 or higher (Tested on Java 25 LTS)
• GNU Make

On Ubuntu / Debian:

sudo apt-get update
sudo apt-get install openjdk-17-jdk make

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Compilation and Execution

# Compile all Java sources
make

# Run the interactive application
make run

# Clean compiled class files
make clean

Optional Data Ingestion

The application supports populating initial catalog and user records from an external formatted text file at launch:

java -cp bin -Dimport=<path-to-file> bci.app.App

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Known Limitations

• Binary Serialization Coupling: System state persistence relies on native Java Object Serialization, requiring binary class compatibility and preventing external query inspection without deserialization.
• In-Memory Collection Traversal: Catalog search and user query operations evaluate through in-memory collection streams rather than persistent indexing structures.

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Credits

• David Vasques (@DeastV), Bruno Fontenele (@brunomatos2505)
• Collaborative group coursework developed for Programação com Objetos (PO) at Instituto Superior Técnico, Universidade de Lisboa. Terminal dialog framework (pt/tecnico/uilib) provided by the teaching staff.