How to use `@ Value` annotation in spring with Kotlin?

# spring

[Manoj]

How to use @ Value annotation in spring with Kotlin?

[Sam]

Same as Java, except that because the $ has special meaning in Kotlin strings, you need to escape it with \

[Sam]

For example @Value("\${my.config.property}")

[Manoj]

But I am facing trouble, the value is not getting assigned. I am currently initializing it as lateinit var

[Sam]

Interesting, I haven't come across that problem. I normally inject values into the constructor instead of into lateinit properties. Can you share an example of the code?

[Manoj]

@Component
class MongoClient {

    @Value("\${mongodb.host}")
    private lateinit var host: String
}

[Sam]

I believe that should work 😕

[Manoj]

If you are injecting values via constructor. Do you pass some random value while initializing new object everytime?

[Sam]

Constructor injection would look like this:

@Component
class MongoClient(@Value("\${mongodb.host}") private val host: String) {
    ...
}

[Manoj]

Yeah but everttime, how you create new object of this class?

[Sam]

Spring creates it for you, so you never actually have to call the constructor

[Sam]

Perhaps this is the problem you're encountering with your lateinit var

[Sam]

Are you trying to create the MongoClient directly via its constructor, like MongoClient()?

[Manoj]

yeah

[Sam]

That won't work with Spring; it needs to create the object itself in order for it to be aware of the injected values and properties within it

[Manoj]

Okay. my requirement is to create a mongoclient and return it. Is there a better way to do it?

[Sam]

Depends on your application, but normally, when you need the MongoClient, you should get hold of it by injection. This isn't really specific to Kotlin, it's a general Spring topic. I would suggest following a tutorial on Spring dependency injection.

[Manoj]

cool thanks.