Custom auto-configuration in Spring Boot - Performance & Optimization

Performance: Custom auto-configuration

MEDIUM IMPACT

Custom auto-configuration affects application startup time and memory usage by adding or skipping bean creation during Spring Boot app initialization.

Adding custom auto-configuration to a Spring Boot app

Spring Boot

package com.example.autoconfig;

import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@ConditionalOnClass(HeavyService.class)
@ConditionalOnProperty(prefix = "myapp.heavy", name = "enabled", havingValue = "true", matchIfMissing = false)
public class MyAutoConfig {

    @Bean
    public HeavyService heavyService() {
        return new HeavyService();
    }
}

Creates HeavyService bean only if class is present and property enabled, reducing startup overhead.

📈 Performance GainAvoids unnecessary bean creation; startup faster by 100-200ms; saves memory

Adding custom auto-configuration to a Spring Boot app

Spring Boot

package com.example.autoconfig;

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

@Configuration
public class MyAutoConfig {

    @Bean
    public HeavyService heavyService() {
        return new HeavyService();
    }
}

Always creates HeavyService bean regardless of app needs, increasing startup time and memory use.

📉 Performance CostBlocks startup for extra 100-200ms; adds unnecessary memory usage

Performance Comparison

Pattern	Bean Creation	Startup Delay	Memory Usage	Verdict
Unconditional bean creation	Always creates bean	Adds 100-200ms delay	Higher memory use	[X] Bad
Conditional bean creation	Creates bean only if needed	No extra delay if skipped	Lower memory use	[OK] Good

Rendering Pipeline

During Spring Boot startup, auto-configuration classes are scanned and conditionally loaded. Beans are created if conditions match, affecting initialization time and memory allocation.

→Bean Definition Loading

→Bean Creation

→Application Context Initialization

⚠️ BottleneckBean Creation stage is most expensive when unnecessary beans are created.

Optimization Tips

1Use @Conditional annotations to load beans only when needed.

2Avoid creating heavy beans unconditionally to reduce startup time.

3Measure startup performance with Spring Boot Actuator tools.

Performance Quiz - 3 Questions

What is the main performance benefit of using conditional annotations in custom auto-configuration?

A They delay bean creation until the first method call.

B They increase the number of beans created to improve functionality.

C They prevent unnecessary bean creation, reducing startup time and memory use.

D They automatically optimize database queries.

DevTools: Spring Boot Actuator / Application Startup Analyzer

How to check: Enable Spring Boot Actuator and use the startup endpoint or ApplicationStartup API to measure bean creation times and startup phases.

What to look for: Look for beans that take long to create or are created unnecessarily; check if conditional annotations reduce startup time.