Spring Boot

What is Spring Boot?

Spring Boot is an opinionated framework built on top of Spring that simplifies the setup and development of Spring applications. It provides:

Auto-configuration: Automatically configures Spring beans based on classpath dependencies
Starter dependencies: Curated dependency bundles (e.g., spring-boot-starter-web)
Embedded server: Tomcat, Jetty, or Undertow embedded — no WAR deployment needed
Production-ready features: Health checks, metrics, externalized configuration
No XML configuration: Convention over configuration

Auto-configuration and @SpringBootApplication

package com.example;

import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.context.annotation.*;

// @SpringBootApplication combines:
// @Configuration       - Java config class
// @EnableAutoConfiguration - Enable Spring Boot auto-config
// @ComponentScan       - Scan for @Component, @Service, etc.
@SpringBootApplication
// Exclude specific auto-configurations if needed:
// @SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class Application {

    public static void main(String[] args) {
        // Customize SpringApplication
        SpringApplication app = new SpringApplication(Application.class);
        app.setBannerMode(Banner.Mode.OFF); // Disable startup banner
        app.run(args);
    }
}

// ApplicationRunner: runs code after application starts
@Component
public class StartupRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("Application started successfully!");
        // args.getOptionValues("server.port") - access command line args
    }
}

Profiles

Spring profiles allow you to have different configurations for different environments (dev, test, prod):

Spring Profiles

// Profile-specific beans
@Configuration
public class DataSourceConfig {

    @Bean
    @Profile("dev")
    public DataSource devDataSource() {
        // H2 in-memory database for development
        return new EmbeddedDatabaseBuilder()
                .setType(EmbeddedDatabaseType.H2)
                .build();
    }

    @Bean
    @Profile("prod")
    public DataSource prodDataSource() {
        // MySQL for production
        HikariDataSource ds = new HikariDataSource();
        ds.setJdbcUrl("jdbc:mysql://prod-server:3306/mydb");
        return ds;
    }
}

// Activate profile:
// application.properties: spring.profiles.active=dev
// Command line: java -jar app.jar --spring.profiles.active=prod
// Environment variable: SPRING_PROFILES_ACTIVE=prod

# application-dev.properties (active when profile=dev)
server.port=8080
spring.datasource.url=jdbc:h2:mem:devdb
spring.jpa.hibernate.ddl-auto=create-drop
logging.level.com.example=DEBUG

# application-prod.properties (active when profile=prod)
# server.port=80
# spring.datasource.url=jdbc:mysql://prod-server:3306/mydb
# spring.jpa.hibernate.ddl-auto=validate
# logging.level.com.example=WARN

Spring Boot Actuator

Actuator Configuration

# Actuator endpoints
management.endpoints.web.exposure.include=health,info,metrics,env,beans
management.endpoint.health.show-details=always
management.info.env.enabled=true

# Custom info
info.app.name=My Spring App
info.app.version=1.0.0
info.app.description=A sample Spring Boot application

# Actuator endpoints (after adding spring-boot-starter-actuator):
# GET /actuator/health  - Application health status
# GET /actuator/info    - Application info
# GET /actuator/metrics - Application metrics
# GET /actuator/env     - Environment properties
# GET /actuator/beans   - All Spring beans
# GET /actuator/mappings - All request mappings

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Spring Boot

What is Spring Boot?

Profiles

Spring Boot Actuator

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