Annotation Injection for Spring with Kotlin - spring

Question

Kotlin cannot inject annotation at compile time such as by existing library Lombok. Is there any decent way to inject annotation for spring framework at runtime?

Answer 1

Assuming you are trying to inject logger annotation into Spring application.
Here's annotation class example: Log.kt
package com.example.util
#Retention(AnnotationRetention.RUNTIME)
#Target(AnnotationTarget.FIELD)
#MustBeDocumented
annotation class Log
This class injects annotation at runtime: LogInjector.kt
package com.example.util
import org.slf4j.LoggerFactory
import org.springframework.beans.BeansException
import org.springframework.beans.factory.config.BeanPostProcessor
import org.springframework.stereotype.Component
import org.springframework.util.ReflectionUtils
import java.lang.reflect.Field
#Component
class LogInjector: BeanPostProcessor {
#Throws(BeansException::class)
override fun postProcessAfterInitialization(bean: Any, beanName: String): Any {
return bean
}
#Throws(BeansException::class)
override fun postProcessBeforeInitialization(bean: Any, name: String): Any {
ReflectionUtils.doWithFields(bean.javaClass,
#Throws(IllegalArgumentException::class, IllegalAccessException::class) { field: Field ->
// SAM conversion for Java interface
ReflectionUtils.makeAccessible(field)
if (field.getAnnotation(Log::class.java) != null) {
val log = LoggerFactory.getLogger(bean.javaClass)
field.set(bean, log)
}
}
)
return bean
}
}
Then, this class uses #Log annotation: GreetingController.kt
package com.example.web
import org.slf4j.Logger
import org.springframework.web.bind.annotation.*
#RestController
class GreetingController {
#Log lateinit private var logger: Logger
#RequestMapping("/greeting")
fun greeting(): String {
logger.info("Greeting endpoint was called")
return "Hello"
}
}
To avoid calling logger in null-safe like logger?.info('...'), this example marks the property with the late-initialized modifier.