Why do big enterprise companies like Java + Spring Boot as their backend?

Why not? Decent enough language for modern development, the Java ecosystem is very well established, and it's easier to find Java devs than a lot of other languages.

Huh? I think they have to, since they invested in it. Other than that...

@molaram the same as Javascript, just without the script /s.

Most of those are locked into the Java ecosystem by sheer monolitic architecture.

- platform independent

- easy deployment

- a lot of programmers that know Java

- fast evolving language and optionally Kotlin

- Good and powerful framework

- Established Spring ecosystem with tons of addons and security updates all the time.

- popular since Netflix uses it

There's a lot of reasons to use Spring for backend. You can build a great backend with a few dozen lines sprinkled across a few dozen classes and some dependencies, and voila, you have an entire API with database access, pretty ORM and auto-documentation for FE to work with.

@magicMirror where I work it's mostly Java/kotlin. Spring boot kinda tries to go against the monolith approach as it makes it easy to get multiple services up and running with a decent architecture. Think the OP is not talking about 7 years ago Java 8 crap

@hjk101 Java Online Services can be broken down into seperate components, and delivered as part of a diverse stack. The reason most of these places use Java is the same reason as banks using Cobol - regulation, and cost of migration to newer stacks. In defence Java - it is actually better at thread managment then say, Ruby, or Python - by being able to actually use Threads that is.
@molaram Java is a usable languague with a thriving eco system, and lots of big projects using it. Look at Elastic Search, or fuking Attlassisn for example. Jenkins. Android dev. Burp Proxy. If you don't like using it - go for something else. Like Go. Or rust. Haskel. Or maybe javascript (shudder).

Java is ok to use. Just don't get yourself locked into it by using a Good Contract based Arch, that uses json, or protobuf to pass data around.

Why not? It's been around for a while, is battle tested, fairly stable. You don't need to mess with compilers. It's not the Wild West of dynamic languages.