When I was learning Spring Boot and building my own project for practice, I ran into something that confused me. My service was taking around 2-4 seconds to start in dev mode. No database connections, no heavy dependencies, just a basic application. I thought maybe that was just how Spring worked, but 4 seconds felt wrong for something so simple. So I started digging into what was actually happening during startup. Turns out, I had more than 20 beans being auto-created at startup. Some of those @Component classes? Never actually used in the flow I was testing. I also had a circular dependency between two services that was quietly delaying initialization, and several @PostConstruct methods were doing I/O operations right during startup. This is what I learned is the hidden cost of Spring Boot’s magic. Every @Component, every @Service, every @Bean you declare adds to your startup time. When you’re learning and experimenting, it’s easy to just annotate everything because the framework makes it so convenient. Here’s what I learned from debugging this: a) First, be intentional about what you mark as a Spring bean. Don’t just annotate everything “just in case” you might need it later. b) Second, use @Lazy for heavy beans that aren’t needed immediately. Let them initialize when they’re actually called. c) Third, move I/O operations out of @PostConstruct. Listen for ApplicationReadyEvent instead, so your app can finish starting up first. And finally, profile your startup time. Use the –debug flag or Spring Boot Startup Actuator to see what’s actually happening under the hood. After these changes, I got the startup time down significantly. #springboot #java #coding
Sreesuman N
6mo
Well said and understanding the background work really important then we can avoid unnecessary calls it make applications load faster.
Igor Queiroz
6mo
And if, by any chance, you built your application using Spring Initializr, you will probably have some default unit test class testing something irrelevant during the process.
Krishna Tulaskar
6mo
Very insightful 💯
Good observation and useful information for beginners.In spring boot 2.6 onwards, if circular dependency exists, application will fail to start.