Study of Java JPA

Este README também está disponível em Português Brasileiro.

This project demonstrates how to implement a clean, test-driven backend architecture using the Java Persistence API (JPA) with PostgreSQL and JUnit 5. It focuses on reusability and separation of concerns through a Generic DAO pattern and fully annotated entity classes.

🚀 Key Features

• ✅ JPA-based persistence with PostgreSQL;
• ✅ Generic DAO structure for all entities using GenericDAO<T> and IGenericDAO<T>;
• ✅ Domain entities: Course, Enrollment, and Product with validation constraints and sequence generation;
• ✅ JPQL-based dynamic queries for search and update operations;
• ✅ JUnit 5 test classes covering full CRUD functionality for all DAOs;
• ✅ Automatic ID management using @SequenceGenerator and @GeneratedValue;
• ✅ JPA configuration via persistence.xml with PostgreSQL connection and Hibernate properties;
• ✅ Full Javadoc coverage added for all entities, DAOs, generic classes, and test suites, including @link references for better navigation;
• ✅ Comprehensive relationship mappings including One-To-Many, Many-To-Many, and One-To-One between entities;
• ✅ Achieved 100% test coverage across all project modules.

🗂️ Project Structure

• br.com.eaugusto.domain: Contains all JPA entity classes;
• br.com.eaugusto.dao: Interfaces and classes for each entity DAO;
• br.com.eaugusto.dao.generic: Reusable generic DAO interface and implementation;
• br.com.eaugusto.dao.interfaces: Dedicated package for DAO interfaces to organize code;
• src/test/java: Unit test classes covering all DAO methods and entity operations, including relationship tests;
• src/main/java/META-INF/persistence.xml: JPA configuration file.

🧪 Testing Approach

• ✅ Built entirely with JUnit 5 using assertions and lifecycle annotations (@BeforeEach, @AfterEach);
• ✅ Test coverage includes insert, update, search by ID, search all, and delete operations;
• ✅ Relationship integrity tested with entity associations (One-To-Many, Many-To-Many, One-To-One);
• ✅ Time-based tests for Instant comparisons use ChronoUnit.MILLIS for accuracy;
• ✅ All tests run using a PostgreSQL database configured via persistence.xml.

📋 Technologies Used

• Java 17+;
• JPA 2.2 (Jakarta Persistence);
• PostgreSQL 14+;
• Hibernate 5.6.2.Final;
• JUnit 5 for testing;
• pgAdmin 4;
• Spring Tools Suite 4.

📑 Learning Objectives

• Understand how JPA annotations map Java classes to database tables;
• Implement a generic DAO architecture for entity management;
• Use JPQL for dynamic queries with entity classes;
• Apply TDD and verify data persistence using comprehensive unit tests;
• Manage complex entity relationships and cascading operations;
• Document code thoroughly with Javadocs for maintainability.

⚙️ Configuration

All persistence settings can be adjusted in the persistence.xml file located in src/main/java/META-INF/. You can configure:

• Database URL;
• Username and password;
• Hibernate dialect and schema generation strategy;
• SQL logging options for debugging purposes.