Java Backend Fundamentals

A hands-on learning repository documenting my journey through Java backend development. This repository contains small practice projects and experiments covering core Java backend technologies, persistence, web development, and the Spring ecosystem.

Learning Roadmap

The projects are organized as individual learning modules:

• JDBC
• Servlets
• Hibernate
• Spring Core
• Spring Java Configuration
• Spring XML Configuration
• Spring JDBC
• Spring Data JPA
• Spring MVC
• Spring Boot

Projects

Project	Topics
jdbc-practice	JDBC, database connections, SQL, CRUD
servlet-practice	Servlets, HTTP, Tomcat, request/response
hibernate-practice	Hibernate ORM, entities, sessions, persistence
spring-java-configuration	Spring IoC and Java-based configuration
spring-xml-configuration	Spring IoC and XML-based configuration
spring-jdbc	Spring JDBC and database access
spring-data-jpa-demo	Spring Data JPA and repository abstraction
spring-boot-mvc-demo	Spring Boot, MVC, controllers, web applications

JDBC Fundamentals

The JDBC practice project focuses on database connectivity and core JDBC operations using PostgreSQL.

Learned

• JDBC database connectivity with DriverManager
• Connection, Statement, and ResultSet
• executeQuery() and executeUpdate()
• CRUD operations: INSERT, SELECT, UPDATE, DELETE
• PreparedStatement and parameterized SQL
• Batch processing with addBatch() and executeBatch()
• Transaction management with commit() and rollback()
• DatabaseMetaData and ResultSetMetaData
• Try-with-resources for JDBC resource management
• Maven dependency management for the PostgreSQL JDBC driver

Project Structure

jdbc-practice/
├── pom.xml
└── src/
    └── main/
        └── java/
            ├── Main.java
            ├── ConnectionDemo.java
            ├── StatementDemo.java
            ├── CrudDemo.java
            ├── PreparedStatementDemo.java
            ├── BatchDemo.java
            ├── TransactionDemo.java
            └── MetadataDemo.java
            

Servlet Fundamentals

Learned

• Embedded Tomcat
• Servlet registration and URL mapping
• Context path vs servlet path
• HTTP request and response
• HttpServletRequest
• HttpServletResponse
• doGet(), doPost(), doPut(), doDelete()
• Servlet lifecycle: init() and destroy()

Example

The Servlet practice project uses embedded Tomcat and maps:

http://localhost:8080/greetings/hello

Hibernate Fundamentals

The Hibernate practice project covers ORM fundamentals, JPA entity mapping, persistence, HQL, entity lifecycle, persistence context, transactions, relationships, and fetch strategies using PostgreSQL.

Hibernate Setup

• Maven project setup
• Hibernate ORM dependency configuration
• PostgreSQL JDBC driver
• hibernate.cfg.xml
• Database connection and dialect configuration
• SessionFactory creation
• Session management
• SessionFactory lifecycle and resource management

JPA Entity Mapping

• @Entity
• @Id
• @GeneratedValue
• @Column
• @Table
• Entity-to-table mapping
• Field-to-column mapping
• Generated primary keys

Session & Transactions

• SessionFactory
• Session
• Transaction
• beginTransaction()
• commit()
• rollback()
• Transaction boundaries
• Basic transaction failure handling

Entity Lifecycle

• Transient state
• Persistent state
• Detached state
• persist()
• detach()
• Entity state transitions
• Dirty checking of persistent entities

CRUD Operations

• persist() for inserting entities
• find() for retrieving entities
• getReference() for obtaining entity references
• Updating persistent entities
• Automatic updates through dirty checking
• remove() for deleting entities

HQL

• HQL SELECT
• WHERE conditions
• Parameterized HQL queries
• LIKE
• ORDER BY
• Aggregate functions
• COUNT()
• AVG()
• HQL JOIN
• JOIN FETCH

Query API

• createQuery()
• Typed HQL queries
• setParameter()
• getResultList()
• getSingleResult()

Persistence Context

• Persistence context
• First-level cache
• Entity identity within a persistence context
• Dirty checking
• flush()
• refresh()
• clear()
• detach()
• Synchronization between entities and the database

Entity Relationships

• Entity relationships and foreign keys
• @OneToMany
• @ManyToOne
• mappedBy
• Relationship ownership
• Cascade operations
• Bidirectional relationships
• Collection mapping
• Foreign-key based associations

Fetch Strategies

• FetchType.LAZY
• FetchType.EAGER
• Lazy loading
• Explicit initialization of lazy associations
• JOIN FETCH
• Difference between lazy and eager loading

Exception Handling

• Hibernate exception handling
• Transaction failure handling
• Rollback on operation failure
• Handling invalid entity operations
• Resource cleanup with try-with-resources

Project Structure

hibernate-practice/
├── pom.xml
├── src/
│   └── main/
│       ├── java/
│       │   ├── ConfigurationDemo.java
│       │   ├── CrudDemo.java
│       │   ├── EntityLifecycleDemo.java
│       │   ├── ExceptionDemo.java
│       │   ├── FetchTypeDemo.java
│       │   ├── HibernateUtil.java
│       │   ├── HqlDemo.java
│       │   ├── Laptop.java
│       │   ├── Main.java
│       │   ├── PersistenceContextDemo.java
│       │   ├── RelationshipDemo.java
│       │   ├── Student.java
│       │   └── TransactionDemo.java
│       └── resources/
│           └── hibernate.cfg.xml