Optimizing the startup time and reducing memory usage in a Spring Boot application involves various techniques and depends on the specific characteristics of your application. Below, I'll provide a simple Spring Boot demo application along with some optimization tips:

1. Use Lazy Initialization:

To reduce memory usage, you can use the @lazy annotation to load beans only when they are needed.

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Lazy;

@Configuration
public class MyConfig {

    @Bean
    @Lazy
    public MyBean myBean() {
        return new MyBean();
    }
}

2. Minimize Auto-Configuration:

Disable unnecessary auto-configurations in your application.properties or application.yml file.

spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration

3. Profile-Specific Configuration:

Use profiles to load configurations selectively based on the environment.

@Configuration
@Profile("dev")
public class DevConfig {
    // Configuration for the "dev" profile
}

4. Reduce Dependencies:

Only include dependencies that your application truly needs. Use a tool like Spring Boot's spring-boot-starter-parent to manage dependencies effectively.

5. Classpath Scanning:

Limit classpath scanning to only necessary packages.

@SpringBootApplication(scanBasePackages = "com.example")
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

6. Garbage Collection Tuning:

Adjust JVM garbage collection settings according to your application's memory requirements. You can set these in your application.properties or application.yml file.

# Example JVM memory settings
spring.profiles.active=dev
server.port=8080

# JVM memory settings
# Adjust these based on your application's requirements
java.security.egd=file:/dev/./urandom
server.tomcat.max-threads=10
server.tomcat.max-connections=10

7. Use Spring Boot's Actuator:

Spring Boot Actuator provides various endpoints for monitoring and managing your application. It can help you diagnose performance bottlenecks.

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

8. JVM Version:

Ensure you are using a compatible and up-to-date JVM version that includes performance improvements.

These tips provide a starting point for optimizing your Spring Boot application. Remember that optimization is often an iterative process, and you should measure the impact of changes using profiling tools and monitoring to ensure that you are achieving the desired improvements in startup time and memory usage.

Efficiently Optimizing Spring Boot Applications: Faster Startup and Lower Memory Usage