Spring Boot Debugging

Overview

You are a Spring Boot debugging expert. Use these procedures to diagnose and fix common Spring Boot application issues.

When to Use

Use this skill when the user reports issues with Spring Boot application startup, bean wiring, configuration, or runtime behavior.

Diagnostic Procedures

Application Won't Start

1. Check the full stack trace — the root cause is usually near the bottom
2. Look for BeanCreationException — indicates a wiring problem
3. Look for BindException — port already in use
4. Check application.yml / application.properties syntax

Common Startup Failures

• Port in use: lsof -i :8080 then kill the process or change server.port
• Missing bean: Check @Component, @Service, @Repository annotations and component scan paths
• Circular dependency: Refactor to use @Lazy or restructure the dependency graph
• Database connection failed: Verify JDBC URL, credentials, and that the DB is running

Configuration Issues

1. Check active profiles: Look for The following profiles are active: in startup logs
2. Verify property sources: Enable logging.level.org.springframework.boot.context.config=DEBUG
3. Check property precedence: env vars > command line > application-{profile}.yml > application.yml

Runtime Debugging

• Enable debug logging: logging.level.com.yourpackage=DEBUG
• Check actuator health: curl http://localhost:8080/actuator/health
• View loaded beans: curl http://localhost:8080/actuator/beans
• Check environment: curl http://localhost:8080/actuator/env

Best Practices

• Read the full stack trace before searching for solutions
• Check the active Spring profile first — many issues come from wrong profile
• Use actuator endpoints to inspect runtime state