Today I discovered that in Kotlin Spring (JVM) whe...

# spring

[Michael Böiers]

Today I discovered that in Kotlin Spring (JVM) when I define a @Service with a method that declares default parameter values and then call the service from another @Component not supplying a value, there is a NoSuchMethodError thrown. Apparently Spring creates a (Java) proxy for the service which does not support default parameter values (not supported in Java).

Is there a solution for this problem?

[Robert Jaros]

Spring doesn't always create proxies. I'm using @Service annotated components with methods with default parameters without problems.

[Robert Jaros]

There are likely specific cases when proxies are used, unfortunately I don't know what they are.

[Michael Böiers]

Usually AOP triggers the use of Proxies. I don‘t need them, but the annoying point is that the code compiles and then fails at runtime …

[Ben]

code compiles and then fails at runtime

That is the major downside of using a framework like spring where it builds the dependency graph at runtime.

[Michael Böiers]

It‘s not so much a dependency problem, it’s the implicit code generation that is enabled elsewhere (not in the code it affects).

[Thomas]

Transactional annotation is creating proxies I guess

[wakingrufus]

I assume if you use functional bean declaration, it won't create proxies, but then you can't use any AOP annotations either

[corneil]

One way to overcome this is to create a Configuration annoted class with Bean annotated method to create the service yourself.

[wakingrufus]

Oh I didn't realize that prevents the proxy

[Michael Böiers]

@corneil sure, there are workarounds - but it kind of spoils the experience. For my project the decision will be to move away from Spring. I’ve always wanted to try Ktor 😎

[corneil]

If you want the bean to support the transactions like with the Transactional annotation you can use TransactionProxyFactoryBean

[Michael Böiers]

I don’t need or want any transaction. The problem is that Spring proxies the service anyway, even though it does not have any aop-requiring annotations.

[corneil]

With Configuration classes and bean methods you skip the proxies

[wakingrufus]

the proxies are there for all the automagical building of the dependency graph with component scans. i prefer to avoid all that by using the functional bean declarations in spring boot 2.x (which can be extended even further such as in the spring-fu project, which create a very ktor-like API for spring boot)

[Michael Böiers]

I’d rather not use Spring altogether in my project. I just did because I was used to, I think Ktor would be a better fit.

[Michael Böiers]

But I’ll check out spring-fu, thanks for the tip 🙂