Spring Boot Basics Skill

Master Spring Boot fundamentals including auto-configuration, starters, externalized configuration, and profile management.

Overview

This skill provides comprehensive knowledge for building production-ready Spring Boot applications from scratch.

Parameters

Name	Type	Required	Default	Validation
spring_version	string	✗	3.3.x	Semver format
java_version	number	✗	21	17, 21, or 23
build_tool	enum	✗	maven	maven | gradle
packaging	enum	✗	jar	jar | war

Topics Covered

Core (Must Know)

• Auto-Configuration: How Spring Boot auto-configures beans based on classpath
• Starters: Pre-configured dependency sets for common scenarios
• Application Properties: Externalized configuration with application.properties/yml
• Profiles: Environment-specific configuration with @Profile

Intermediate

• Configuration Properties: Type-safe configuration with @ConfigurationProperties
• Actuator: Production-ready monitoring and management endpoints
• Logging: Logback/Log4j2 configuration and best practices
• DevTools: Development-time features for productivity

Advanced

• Custom Starters: Building reusable starter modules
• Auto-Configuration Classes: Creating custom auto-configuration
• Conditional Beans: @ConditionalOnProperty, @ConditionalOnClass
• Native Compilation: GraalVM native image support

Code Examples

Basic Application

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

Configuration Properties

@ConfigurationProperties(prefix = "app")
@Validated
public record AppConfig(
    @NotBlank String name,
    @NotNull Database database,
    List<String> allowedOrigins
) {
    public record Database(
        @NotBlank String url,
        String username,
        String password,
        @Min(1) @Max(100) int poolSize
    ) {}
}

# application.yml
app:
  name: my-service
  database:
    url: jdbc:postgresql://localhost:5432/mydb
    username: ${DB_USER}
    password: ${DB_PASSWORD}
    pool-size: 10
  allowed-origins:
    - http://localhost:3000
    - https://myapp.com

Profile-Specific Configuration

# application-dev.yml
spring:
  config:
    activate:
      on-profile: dev
  datasource:
    url: jdbc:h2:mem:devdb

---
# application-prod.yml
spring:
  config:
    activate:
      on-profile: prod
  datasource:
    url: jdbc:postgresql://${DB_HOST}:5432/proddb

Actuator Configuration

management:
  endpoints:
    web:
      exposure:
        include: health,info,metrics,prometheus
  endpoint:
    health:
      show-details: when_authorized
      probes:
        enabled: true

Retry Logic

Scenario	Max Retries	Backoff	Notes
Config server connection	6	1s, 1.5x multiplier	Use spring.config.import
Database connection	3	2s exponential	Configure in connection pool

Troubleshooting

Failure Modes

Issue	Diagnosis	Fix
Bean not created	Check @ConditionalOn*	Run with --debug flag
Property not binding	Wrong prefix or type	Validate YAML syntax
Profile not active	Not set in env	Use -Dspring.profiles.active

Debug Checklist

□ Run with --debug to see auto-configuration report
□ Verify property sources with /actuator/env
□ Confirm active profiles with /actuator/info
□ Check application.yml indentation

Unit Test Template

@SpringBootTest
class ApplicationConfigTest {

    @Autowired
    private AppConfig appConfig;

    @Test
    void shouldLoadConfiguration() {
        assertThat(appConfig.name()).isEqualTo("my-service");
        assertThat(appConfig.database().poolSize()).isEqualTo(10);
    }
}

Usage

Skill("spring-boot-basics")

Version History

Version	Date	Changes
2.0.0	2024-12-30	Production-grade with examples, troubleshooting
1.0.0	2024-01-01	Initial release