Spring Boot Debugging Guide

You are an expert Spring Boot debugger. Follow this systematic approach to diagnose and resolve issues efficiently.

Common Error Patterns

1. NoSuchBeanDefinitionException

Symptoms:

• "Field xyz required a bean of type 'X' that could not be found"
• "No qualifying bean of type 'X' available"

Debugging Steps:

1. Verify the class has @Component, @Service, @Repository, or @Controller annotation
2. Check if the class is in a package scanned by @ComponentScan (must be in or below @SpringBootApplication class package)
3. Verify @Configuration classes with @Bean methods are being loaded
4. Check for conditional annotations (@ConditionalOnProperty, @Profile) that might exclude the bean
5. Look for typos in qualifier names with @Qualifier

Quick Fixes:

// Ensure main class is at root package
@SpringBootApplication
public class Application { ... }

// Explicit component scan if needed
@ComponentScan(basePackages = {"com.example.main", "com.example.other"})

// Check bean registration
@Autowired
private ApplicationContext context;
Arrays.stream(context.getBeanDefinitionNames()).forEach(System.out::println);

2. Application Failed to Start

Symptoms:

• "Web server failed to start. Port 8080 was already in use"
• "Application run failed"
• Context initialization errors

Debugging Steps:

1. Check for port conflicts: lsof -i :8080 or netstat -an | grep 8080
2. Review full stack trace for root cause (scroll up past Spring banner)
3. Check database connectivity if using JPA
4. Verify all required environment variables are set
5. Look for missing dependencies in pom.xml or build.gradle

Quick Fixes:

# Change port if in use
server.port=8081

# Enable debug startup logging
debug=true
logging.level.org.springframework=DEBUG

# Fail fast on missing properties
spring.main.allow-bean-definition-overriding=false

3. Circular Dependency

Symptoms:

• "The dependencies of some of the beans in the application context form a cycle"
• "Requested bean is currently in creation"

Debugging Steps:

1. Read the cycle chain in error message (A -> B -> C -> A)
2. Identify which dependency can be broken
3. Consider if the design needs refactoring

Quick Fixes:

// Option 1: Use @Lazy on one dependency
@Autowired
@Lazy
private ServiceB serviceB;

// Option 2: Use setter injection
private ServiceB serviceB;

@Autowired
public void setServiceB(ServiceB serviceB) {
    this.serviceB = serviceB;
}

// Option 3: Refactor to event-based communication
@EventListener
public void handleEvent(CustomEvent event) { ... }

4. JPA/Hibernate Issues

Symptoms:

• "No EntityManager with actual transaction available"
• LazyInitializationException
• "Table doesn't exist" / Schema validation errors
• N+1 query problems

Debugging Steps:

1. Enable SQL logging to see actual queries
2. Check @Transactional placement (must be on public methods)
3. Verify entity relationships and cascade types
4. Check database schema matches entity definitions

Quick Fixes:

# Enable SQL debugging
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true
logging.level.org.hibernate.SQL=DEBUG
logging.level.org.hibernate.type.descriptor.sql.BasicBinder=TRACE

# Schema handling
spring.jpa.hibernate.ddl-auto=validate  # Recommended for debugging
spring.jpa.hibernate.ddl-auto=update    # Auto-update schema (dev only)

// Fix LazyInitializationException
@Transactional(readOnly = true)
public Entity getWithChildren(Long id) {
    Entity e = repository.findById(id).orElseThrow();
    e.getChildren().size(); // Force initialization
    return e;
}

// Or use EntityGraph
@EntityGraph(attributePaths = {"children", "children.grandchildren"})
Optional<Entity> findById(Long id);

5. Security Configuration Problems

Symptoms:

• 403 Forbidden on all endpoints
• Authentication not working
• CORS errors
• CSRF token issues

Debugging Steps:

1. Enable security debug logging
2. Check filter chain order
3. Verify authentication provider configuration
4. Review SecurityFilterChain bean configuration

Quick Fixes:

# Enable security debugging
logging.level.org.springframework.security=DEBUG
logging.level.org.springframework.security.web.FilterChainProxy=DEBUG

@Configuration
@EnableWebSecurity
public class SecurityConfig {

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/api/public/**").permitAll()
                .requestMatchers("/actuator/health").permitAll()
                .anyRequest().authenticated()
            )
            .csrf(csrf -> csrf.disable()) // Only for APIs with token auth
            .cors(Customizer.withDefaults());
        return http.build();
    }
}

6. Property Binding Failures

Symptoms:

• "Failed to bind properties under 'x.y.z'"
• "Could not resolve placeholder"
• Configuration values not being read

Debugging Steps:

1. Check property file location (src/main/resources)
2. Verify property name matches exactly (case-sensitive, hyphen vs camelCase)
3. Check active profiles (spring.profiles.active)
4. Verify @ConfigurationProperties prefix matches

Quick Fixes:

// Debug property sources
@Autowired
private Environment env;

@PostConstruct
public void debugProperties() {
    System.out.println("Active profiles: " + Arrays.toString(env.getActiveProfiles()));
    System.out.println("Property value: " + env.getProperty("my.property"));
}

// Ensure @ConfigurationProperties is scanned
@EnableConfigurationProperties(MyProperties.class)
@SpringBootApplication
public class Application { ... }

# Add to see property resolution
logging.level.org.springframework.boot.context.properties=DEBUG

Debugging Tools

Spring Boot Actuator

Essential for runtime diagnostics:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

# Expose all actuator endpoints (dev only)
management.endpoints.web.exposure.include=*
management.endpoint.health.show-details=always

Key Endpoints:

• /actuator/health - Application health status
• /actuator/beans - All registered beans
• /actuator/env - Environment properties
• /actuator/mappings - Request mappings
• /actuator/configprops - Configuration properties
• /actuator/conditions - Auto-configuration report

Remote JVM Debugging

# Maven
mvn spring-boot:run -Dspring-boot.run.jvmArguments="-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:5005"

# Gradle
./gradlew bootRun --debug-jvm

# Java directly
java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:5005 -jar app.jar

# Docker Compose
environment:
  - JAVA_TOOL_OPTIONS=-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:5005
ports:
  - "5005:5005"

Logback/Log4j2 Configuration

Create src/main/resources/logback-spring.xml:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/defaults.xml"/>

    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>

    <!-- Debug specific packages -->
    <logger name="org.springframework.web" level="DEBUG"/>
    <logger name="org.hibernate.SQL" level="DEBUG"/>
    <logger name="com.yourapp" level="DEBUG"/>

    <root level="INFO">
        <appender-ref ref="CONSOLE"/>
    </root>
</configuration>

Spring Boot DevTools

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>

Features:

• Automatic restart on code changes
• LiveReload browser integration
• Relaxed property binding in dev
• H2 console auto-configuration

IntelliJ IDEA Spring Debugger (2025.2+)

• View active loaded beans with metadata
• See actual property values inline in .properties/.yaml
• Inspect bean scope, profile, and context
• View database connections
• Navigate to bean definitions

The Four Phases (Spring Boot-specific)

Phase 1: Gather Information

# Check application logs
tail -f logs/spring.log

# Check JVM status
jps -lv
jstat -gc <pid>
jstack <pid>

# Check actuator endpoints
curl localhost:8080/actuator/health
curl localhost:8080/actuator/env
curl localhost:8080/actuator/beans

Phase 2: Reproduce and Isolate

// Create minimal test case
@SpringBootTest(classes = {TestConfig.class, ProblemBean.class})
class IsolatedTest {
    @Autowired
    private ProblemBean bean;

    @Test
    void reproduceIssue() {
        // Minimal steps to reproduce
    }
}

// Use test slices for faster isolation
@WebMvcTest(ProblemController.class)
@DataJpaTest
@JsonTest

Phase 3: Diagnose Root Cause

// Add diagnostic logging
@Aspect
@Component
public class DiagnosticAspect {
    private static final Logger log = LoggerFactory.getLogger(DiagnosticAspect.class);

    @Around("execution(* com.yourapp.service.*.*(..))")
    public Object logMethodExecution(ProceedingJoinPoint jp) throws Throwable {
        log.debug("Entering: {}", jp.getSignature());
        try {
            Object result = jp.proceed();
            log.debug("Exiting: {} with result: {}", jp.getSignature(), result);
            return result;
        } catch (Exception e) {
            log.error("Exception in {}: {}", jp.getSignature(), e.getMessage());
            throw e;
        }
    }
}

Phase 4: Fix and Verify

# Run targeted tests
./mvnw test -Dtest=ProblemTest

# Run full test suite
./mvnw verify

# Check for regressions
./mvnw test -Dtest=*IntegrationTest

Quick Reference Commands

Maven

# Run with debug logging
./mvnw spring-boot:run -Dspring-boot.run.arguments="--debug"

# Run with specific profile
./mvnw spring-boot:run -Dspring-boot.run.profiles=dev

# Skip tests and run
./mvnw spring-boot:run -DskipTests

# Generate dependency tree
./mvnw dependency:tree

# Check for dependency conflicts
./mvnw dependency:analyze

# Force update dependencies
./mvnw clean install -U

Gradle

# Run with debug logging
./gradlew bootRun --args='--debug'

# Run with specific profile
./gradlew bootRun --args='--spring.profiles.active=dev'

# Show dependencies
./gradlew dependencies

# Refresh dependencies
./gradlew build --refresh-dependencies

Docker

# Check container logs
docker logs <container_name> -f

# Shell into container
docker exec -it <container_name> /bin/sh

# Check container health
docker inspect --format='{{.State.Health.Status}}' <container_name>

# View container environment
docker exec <container_name> env | grep SPRING

Kubernetes

# Get pod logs
kubectl logs <pod-name> -f

# Get previous container logs (after crash)
kubectl logs <pod-name> --previous

# Describe pod for events
kubectl describe pod <pod-name>

# Port forward for debugging
kubectl port-forward <pod-name> 5005:5005

# Shell into pod
kubectl exec -it <pod-name> -- /bin/sh

Database Debugging

# Connect to PostgreSQL
psql -h localhost -U user -d database

# Show running queries
SELECT * FROM pg_stat_activity WHERE state = 'active';

# Connect to MySQL
mysql -h localhost -u user -p database

# Show process list
SHOW PROCESSLIST;

JVM Diagnostics

# List Java processes
jps -lv

# Thread dump
jstack <pid> > thread_dump.txt

# Heap dump
jmap -dump:format=b,file=heap.hprof <pid>

# GC stats
jstat -gcutil <pid> 1000

# JVM flags
jinfo -flags <pid>

Debugging Microservices

Distributed Tracing

<!-- Add Micrometer Tracing -->
<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-tracing-bridge-brave</artifactId>
</dependency>
<dependency>
    <groupId>io.zipkin.reporter2</groupId>
    <artifactId>zipkin-reporter-brave</artifactId>
</dependency>

# Zipkin configuration
management.tracing.sampling.probability=1.0
management.zipkin.tracing.endpoint=http://zipkin:9411/api/v2/spans

Correlation IDs

@Component
public class CorrelationIdFilter extends OncePerRequestFilter {
    private static final String CORRELATION_ID = "X-Correlation-ID";

    @Override
    protected void doFilterInternal(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain) {
        String correlationId = request.getHeader(CORRELATION_ID);
        if (correlationId == null) {
            correlationId = UUID.randomUUID().toString();
        }
        MDC.put("correlationId", correlationId);
        response.setHeader(CORRELATION_ID, correlationId);
        try {
            chain.doFilter(request, response);
        } finally {
            MDC.remove("correlationId");
        }
    }
}

Common Gotchas

1. @Transactional on private methods - Does not work, must be public
2. Calling @Transactional method from same class - Bypasses proxy, no transaction
3. Missing @Repository on custom implementations - Exception translation not applied
4. @Value in constructor - Field not yet injected, use @PostConstruct
5. Static fields with @Autowired - Never injected
6. @ComponentScan without basePackages - Only scans current package and below
7. application.properties in wrong location - Must be in src/main/resources root
8. Profile-specific config not loading - Check spring.profiles.active is set

Further Reading

• Spring Boot Reference Documentation
• Spring Framework Core Technologies
• Baeldung Spring Tutorials