com.twitter.util.validation.internal.AnnotationFactory.scala Maven / Gradle / Ivy

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package com.twitter.util.validation.internal

import java.lang.annotation.Annotation
import java.lang.reflect.Method
import java.util
import sun.reflect.annotation.AnnotationParser

private[validation] object AnnotationFactory {

  /**
   * Creates a new Annotation (AnnotationProxy) instance of
   * the given annotation type with the custom values applied.
   *
   * @see [[AnnotationParser.annotationForMap]]
   */
  def newInstance[A <: Annotation](
    annotationType: Class[A],
    customValues: Map[String, Any] = Map.empty
  ): A = {
    val attributes: util.Map[String, Object] = new util.HashMap[String, Object]()
    // Extract default values from annotation
    val methods: Array[Method] = annotationType.getDeclaredMethods
    var index = 0
    val length = methods.length
    while (index < length) {
      val method = methods(index)
      attributes.put(method.getName, method.getDefaultValue)
      index += 1
    }
    // Populate custom values
    val keysIterator = customValues.keysIterator
    while (keysIterator.hasNext) {
      val key = keysIterator.next()
      attributes.put(key, customValues(key).asInstanceOf[AnyRef])
    }
    AnnotationParser.annotationForMap(annotationType, attributes).asInstanceOf[A]
  }
}