DEV Community: Akanksha Soni

I Kept Seeing These Spring Boot Errors — Until I Learned This

Akanksha Soni — Thu, 22 Jan 2026 17:01:08 +0000

Spring Boot makes backend development faster and cleaner, but when something breaks, the error logs can feel overwhelming—especially if you’re new to the framework.

In this post, I’ll walk through some common Spring Boot errors I’ve personally encountered, show realistic error logs, explain why they happen, and share practical fixes that actually work. This guide is aimed at beginner to intermediate developers who want to debug Spring Boot applications with confidence.

1️⃣ Port Already in Use
🔴 Error Log

`Web server failed to start. Port 8080 was already in use.`

🤔 Why this happens

Another application is already running on port 8080
A previous Spring Boot instance didn’t shut down properly

✅ How to fix it

Option 1: Stop the running process

Find the process using port 8080 and stop it

Option 2: Change the application port

server.port=8081

🧠 Tip

Always make sure old instances of your application are stopped before restarting.

2️⃣ BeanCreationException
🔴 Error Log

`Error creating bean with name 'userService':
Unsatisfied dependency expressed through field 'userRepository'`

🤔 Why this happens

Missing Spring annotations like @Service, @Repository, or @Component
Circular dependencies between beans
Package scanning issues

✅ How to fix it

Ensure correct annotations are present
Verify your package structure
Avoid circular dependencies

@Service
public class UserService {
}

3️⃣ NullPointerException
🔴 Error Log

java.lang.NullPointerException: Cannot invoke "User.getId()" because "user" is null

🤔 Why this happens

Object was never initialized
Repository returned null
Missing validation or null checks

✅ How to fix it

Validate inputs
Use Optional when fetching data

Optional<User> user = userRepository.findById(id);

🧠 Tip

Never assume data exists—always handle the null case explicitly.

4️⃣ Failed to Configure a DataSource
🔴 Error Log

Failed to configure a DataSource: 'url' attribute is not specified

🤔 Why this happens

Database credentials are missing
Database server is not running
Incorrect driver dependency

✅ How to fix it

Check your application.properties or application.yml:

spring.datasource.url=jdbc:mysql://localhost:3306/testdb
spring.datasource.username=root
spring.datasource.password=password

5️⃣ 404 Error for Controller APIs
🔴 Error Log

No mapping found for HTTP request

🤔 Why this happens

Incorrect API URL
Missing @RestController
Wrong HTTP method used

✅ How to fix it

Make sure your controller is properly annotated:

@RestController
@RequestMapping("/api/users")
public class UserController {
}

6️⃣ How to Read Spring Boot Logs Effectively

Spring Boot logs can be noisy, but you don’t need to read everything.

✅ Focus on:

The first Caused by message
The exception name
The line number in your code

🚫 Ignore:

Repeated stack trace lines
Framework internals unless required
Learning how to read logs properly will save you hours of debugging time.

🏁 Conclusion

Errors are not a sign that you’re bad at Spring Boot—they’re part of the learning process.

The key is understanding why an error occurs, knowing where to look in the logs, and applying a systematic fix. Over time, debugging becomes less frustrating and more intuitive.

If this post helped you, feel free to share the most confusing Spring Boot error you’ve faced in the comments 👇

🤖 CodeMentor AI — An AI-Powered Code Review Tool

Akanksha Soni — Wed, 14 Jan 2026 04:22:45 +0000

CodeMentor AI is a web-based, AI-powered code review tool designed to help developers instantly analyze code, identify issues, and learn best practices—all in one place.

Problem Statement
As developers:

We don’t always get quick feedback on our code
Bugs, inefficiencies, and bad practices are easy to miss
Manual code reviews take time and depend on availability

CodeMentor AI solves this by providing instant, actionable feedback using AI—helping developers learn and improve faster.

Code Input & Preview

Paste your code snippet directly into the editor

AI-Powered Code Review

With one click, CodeMentor AI:

Detects potential errors and bad practices
Suggests cleaner and more efficient code
Highlights performance improvements
Provides improved code examples
The feedback is clear, structured, and beginner-friendly.

How It Works (High-Level)

User Code Input
      ↓
Frontend UI
      ↓
AI Code Analysis Engine
      ↓
Structured Feedback + Suggestions
      ↓
Optional PDF Export

The system is designed to be lightweight, fast, and easy to deploy locally or online.

Links

📂 GitHub

🎥 Video

Final Thoughts

CodeMentor AI is built to make code reviews faster, smarter, and more accessible.
It demonstrates how AI can assist developers not just by generating code, but by teaching and improving code quality.

Thanks for reading! 👋

Kira — Full-Stack Task & Project Management System

Akanksha Soni — Wed, 14 Jan 2026 03:04:03 +0000

Kira is a full-stack task and project management web application designed to help teams track work efficiently with role-based access, visual dashboards, Kanban workflow, and automated email notifications.

Key Features

JWT Authentication with Admin / User roles
Dashboards with task status & priority charts
Projects & Tasks — full CRUD, filters, CSV/Excel export
Kanban Board — drag & drop status updates
Email Notifications when tasks are assigned
Dark / Light Theme, responsive UI

System Design (High Level)

`Vue.js + Vuetify (Frontend)
   ↓ REST (Axios)
Spring Boot (Backend)
   ↓ JPA / Hibernate
MySQL Database
   ↓
JavaMail → Email Notification`

JWT secures protected APIs
Role-based access handled at backend
Kanban updates sync with dashboards in real time

Screenshots

Links

GitHub Video

Closing
Kira showcases production-style full-stack development, combining secure authentication, analytics dashboards, Kanban workflows, and backend email automation in a single system.