Whether to make the server side at the time of system rebuild with Kotlin or Java

It's a story in a limited number of scenes, but I'll publish it to Qiita because it's a scene that seems to be in the world, and I want to update it if there are any differences or other perspectives. Also, although there are many articles dealing with differences at the fine syntax level, I also wrote that there seemed to be few articles comparing from various perspectives.

Assumptions for comparison

--Rebuild your existing Java system with Spring Boot --Spring Boot is not dealt with here because it is a specific context. --Small language level differences are not compared --Team development with dozens of people

Java

merit

• Performance --Many development achievements including mission-critical systems
• Man --The actual learning cost is low because many people have already paid the learning cost. --Technology --Optional allows null safe at runtime, @Nullable allows null safe at the compiler level ...
• Future ――The aspect of Oracle is fading a little, and the danger is low because various vendors are involved. --Information distribution ――There are new and old ones, but the information that can be obtained is overwhelmingly large. --Reconstruction context --When rebuilding, it can be reused if it is the same language

Demerit

• Man ――There are a lot of Java human resources as a population parameter of engineers, but it tends to be a mixture of boulders.
• Productivity ――Isn't it comparable to the familiar Kotlin engineer? --Reconstruction context At the time of rebuilding, simple copy and paste is possible because it is the same language, and there is a possibility that spoiled code will be mixed even though it is a precious rebuilding.

Kotlin

merit

• Man --When hiring, you can do Kotlin = Increase the probability of being a high-level human resource compared to Java human resources --Technology --Syntax level + Null safe at the compiler level, and the feeling that other pitfalls that tend to occur in Java are prevented at the syntax level
• Productivity ――It's hard to get used to it, but once you get used to it, is it expensive compared to Java? --Reconstruction context --At the time of reconstruction, since it is a different language, it cannot be simply diverted, and it is unlikely to be mixed with spoiled code because it is converted and refactored.

Demerit

• Performance --Aside from Android, there is little track record of being large or complex as a server-side language.
• Man --Since there are few engineers who have paid the learning cost, the learning cost is high.
• Future ――It was developed as OSS mainly by JetBrains, and Google has made it the Android standard, but since there is a JVM, can the departure of Oracle be a risk? --Information distribution --Overwhelmingly less information is available compared to Java --Reconstruction context --When rebuilding, conversion and refactoring are required because it is a different language

reference

-Introduction to Kotlin for Server-Side Java Developers