Spring Boot Done Right: Lessons from a 400-Module Codebase

I worked on a core Spring Boot project for five or six years at a very large enterprise. In my opinion, the most dangerous thing about this framework is that it makes its core users feel far too self-assured.

When looking at problems, your mind becomes consumed with how to force everything into design patterns—like architectural separation, DI, or interface / implementation split. This causes developers to lose sight of the actual essence of the problem because they are obsessed with conforming to the framework.

Because the ecosystem and toolchain surrounding Spring Boot and Java are so mature and well-supported, it is very easy to find community tools that make you feel like you are doing things the "right way."

I only realized these issues after I left Spring Boot and Java development behind. Now, I much prefer using TypeScript or Python to write code (for example, web servers).

I also prefer using various SaaS solutions to handle authentication and user registration rather than rebuilding it all myself with Spring Boot Security. I honestly never want to go back to the days of writing Java again.

Ops person here who has supported Java/SpringBoot applications. I think most of dislike of Java apps comes not from language or framework BUT from fact that most Java using workspaces are filled with mediocracy. They tend to be businesses with products that have extreme moats and thus quality of software barely matters. I imagine most people who would even read this medium article are dreaming of better than that.

There is no right way to do Spring Boot.The entire idea is broken.

Dependency injection is good. It makes it possible to test stuff.

Automagic wiring of dependencies based on annotations is bad and horrible.

If you want to do dependency injection, you should do it the way Go programs do it. Create the types you need in your main method and pass them into the constructors that need them.

When you write tests and you want to inject something else, then create something else and pass that in.

But the idea that you create magic containers and then decorate packages or classes or methods or fields somewhere and then stuff suddenly gets wired into something else via reflection magic is a maintenance nightmare. This is particularly true when some bean is missing, and the one guy who knows which random package out of hundreds has that bean in it is on vacation and the poor schmucks on his team have no clue why their stuff doesn't work.

"I added Spring Boot to our messy Java project."

"Now you have 3 problems."

Does this app take 5 minutes to start? That's so much dynamic Spring magic. Also, how do you keep track of control flow when anything at anytime could have been overridden by something else? It seems like tracing and debugging this thing would be like exploring someone else's codebase every time.

Keep in mind that a big part of the configuration complexity of CAS is because of how it's used and customized in the real world.

These kinds of infrastructure systems its very common to replace a bunch of the built in functionality with your own classes, and so there's alot of effort put into supporting that use case.

I helped build a large open source enterprise financial systems, and most of the deploying orgs used CAS for authN. Both CAS and the financial system was built with similar approach to extensibility.

Hacker news likes to dunk on Spring Boot, but its usage in enterprises is very very high.

Switched from Spring Boot to Ruby on Rails 3 years ago.

I expected to see some new Spring 'tricks' in this post, but it's pretty much regular things that people might do in larger codebases.

- Swap out Java for Kotlin. The Spring guys won't officially drop support for Java; but a lot of their recent releases are becoming very Kotlin centered. Seriously, it's much nicer to use from Kotlin. I've done both.

- Go for declarative Kotlin DSLs over annotation magic for most things. Much easier to debug. It's just function calls. And DSLs are nice in IDEs with autocomplete.

- Keep it simple. It's a huge framework. But you probably don't need most of it.

- Don't go Spring everything, a lot of stuff in Spring is a bit experimental (Spring AI/MCP stuff) or a bit bare bones (Spring Data, it's a limited and extra level of indirection you mostly shouldn't need) or flat out misguided/over-engineered (Spring Batch, good alternatives are available for that).

- Decide on synchronous or asynchronous IO. The former is a lot more scalable now that Java has green threads. The latter is relatively painless from Kotlin but an absolute PITA from Java. They are very different internally and both have their pros/cons. If you need async, Kotlin co-routines is the easier path to do that. Either way, it's one of the bigger decisions to take.

- Don't copy their way of deeply nested inheritance hierarchies. Very much in fashion 20 years ago; a bit of an anti pattern now. Internal code complexity is the part I like least about Spring. And it has some really byzantine stuff in there with 5-6 levels of inheritance or worse.

> What makes the CAS codebase impressive is the discipline of applying all of them consistently, across 400 modules, for years.

I think this is the main point. You can write good code in any language following this concept.

Bodyless classes only for carrying annotations... too much magic for my taste.

I wonder how many of these rules can be enforced with static analysis and ArchUnit.

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I recently inherited java code base.

Just rewrote it in Go. Now we are using a server which consumes 30% of ram what the existing one used to and the latency and throughput have all improved.

Don't use these stupid java backend like sprinboot.