Spring Boot CRUD REST API (No Database) | Learn @GetMapping, @PostMapping & Postman
This is Video 4 of the Spring Boot Project Series.
In this video, we focus on core REST API concepts in Spring Boot by building a CRUD API using an in-memory HashMap, without using any database or JPA.
👉 This approach helps you clearly understand how APIs work before moving to PostgreSQL, JPA, and Hibernate in upcoming videos.
🦜 What you’ll learn in this video
What is a REST API in Spring Boot
Creating APIs using @RestController
Understanding and using:
@GetMapping
@PostMapping
@PutMapping
@DeleteMapping
@PathVariable
@RequestBody
@ResponseBody
Building full CRUD functionality using HashMap
How data is stored in memory (and why it disappears on restart)
How to test REST APIs using Postman
Understanding HTTP methods and request/response flow
🦜 Why we are NOT using a database yet
This video is intentionally database-free
Helps beginners avoid confusion between:
API logic
Database logic
In the next videos, we will:
Replace HashMap with JPA Repository
Connect PostgreSQL
Persist data properly in a real database
🦜 Who this video is for
Beginners learning Spring Boot
Java developers new to REST APIs
Anyone confused about CRUD operations
Developers preparing for backend / Java interviews
Learners who want step-by-step project-based learning
🚀 What’s coming next in this series
Creating real entities
Connecting PostgreSQL
Using Spring Data JPA & Hibernate
Moving logic to Service layer
DTOs & Global Exception Handling
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