Kotlin的弹簧注释注入

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 .