Guava Cache Generic LoadingCache

Question

我正在尝试使用scala创建通用的LoadingCache，并编写了以下代码-

trait GuavaCache[K, V] {
  val maxSize = 1000
  val expirationTime = 10
  val expirationTimeUnit = TimeUnit.MINUTES

  def loadKey(k: K): V

  lazy val cache: LoadingCache[K, V] = CacheBuilder.newBuilder()
    .maximumSize(maxSize)
    .recordStats()
    .expireAfterWrite(expirationTime, expirationTimeUnit)
    .build(new CacheLoader[K,V] {
      override def load(key: K): V = loadKey(key)
    })

}

但是无法编译以上代码，却提示错误为-

Error:(18, 6) overloaded method value build with alternatives:
  [K1 <: Object, V1 <: Object]()com.google.common.cache.Cache[K1,V1] <and>
  [K1 <: Object, V1 <: Object](x$1: com.google.common.cache.CacheLoader[_ >: K1, V1])com.google.common.cache.LoadingCache[K1,V1]
 cannot be applied to (com.google.common.cache.CacheLoader[K,V])
    .build(new CacheLoader[K,V] {

但是大多数博客文章也建议仅以相同的方式进行，https://commitlogs.com/2017/03/11/caching-predictive-models-using-guava-in-scala/

Scala版本-2.12番石榴版本-“ 27.0-jre”

Answer 1

该错误使诊断非常困难，但这很简单。您需要声明您的K和V继承自Object（java.lang.object）。因此解决方法很简单：

trait GuavaCache[K <: Object, V <: Object] { ...