How do I read an environment variable in Kotlin?

问题:

I'd like to get a certain value from an environment variable in my Kotlin app, but I can't find anything about reading environment variables in the core libraries documentation.

I'd expect it to be under kotlin.system but there's really not that much there.

回答1:

It is really easy to get a environment value if it exists or a default value by using the elvis operator in kotlin:

var envVar: String = System.getenv("varname") ?: "default_value"

回答2:

You could always go down this approach:

val envVar : String? = System.getenv("varname")

Though, to be fair, this doesn't feel particularly idiomatic, as you're leveraging Java's System class, not Kotlin's.

回答3:

My favorite one-liner is:

val myEnv = if (System.getenv("MY_ENV").isNullOrEmpty()) "default_value" else System.getenv("MY_ENV")

回答4:

You can use the kotlin extension Konfig

Konfig - A Type Safe Configuration API for Kotlin

Konfig provides an extensible, type-safe API for configuration properties gathered from multiple sources — built in resources, system properties, property files, environment variables, command-line arguments, etc.

For example: Key("http.port", intType)