Trying to call a class with constructor but #Autowired var is throwing Null Pointer Exception in Kotlin/Spring Boot - spring

Question

I'm new to Kotlin and Spring Boot. I'm trying to call SearchService class with initialized constructors through ServiceClass, everything is fine until it's time to access Autowired env variable in SearchService - it throws Null Pointer Exception. I'm assuming I will have to Autowire SearchService in ServiceClass but then how will I initialize the constructor and name/isAlive variables in the performSearch method.
#Service
class ServiceClass {
#Autowired
lateinit var env: Environment
fun performSearch(req: String): String {
var searchService = SearchService("John", false)
result = searchService.searchAsync()
...
return result
}
}
#Repository
class SearchService(name: String = "", isAlive: Boolean = true) {
private var name: String = name
private var isAlive: Boolean = isAlive
#Autowired
lateinit var env: Environment
fun searchAsync(): String {
var endpoint = env.getProperty("endpoint").toString() + name //Error here
// makes call to get endpoint with Name and isAlive as params
...
return result
}
}

Answer 1

You're right that you need need to autowire the SearchService too. Spring can only autowire dependencies into components that it created. Because you're creating the SearchService yourself, Spring doesn't know that it exists, and won't autowire into it.
Your second question is: if you autowire the SearchService, how can you initialise its other properties like name and isAlive? This is a common problem with dependency injection, which arises when some of the parameters to a constructor are dependencies and others are data.
The solution is to use the factory design pattern. In dependency injection it's also sometimes called "assisted injection". Create another "factory" component whose only job is to create the SearchService for you:
#Component
class SearchServiceFactory(private val env: Environment) {
fun createSearchService(name: String = "", isAlive: Boolean = true) =
SearchService(env, name, isAlive)
}
You should then remove the #Repository annotation from the SearchService, since its creation isn't managed directly by Spring.
The factory can be autowired wherever you need to use it, and in turn has the Environment autowired into it. When you want to create the SearchService, you call createSearchService to provide values for the additional data parameters.
Your service class would change to the following:
#Service
class ServiceClass(private val factory: SearchServiceFactory) {
fun performSearch(req: String): String {
var searchService = factory.createSearchService("John", false)
result = searchService.searchAsync()
...
return result
}
}
Note that in the examples I've used constructor injection instead of #Autowired. Spring will automatically provide values for constructor arguments when instantiating a Kotlin class, the same as if it was an autowired field. Using constructor injection instead of field injection can help to ensure that problems like the one you encountered are detected at compile time rather than causing null pointer exceptions at runtime.