如何将Java Builder模式与含可选字段的Scala样例类结合？

在Scala开发中，我们常会用到采用Builder模式的Java API（比如Google Maps Java Client）。通常我们会用Scala样例类收集参数，并用Option类型处理可选值，但原始写法会产生大量重复的map+getOrElse代码，显得繁琐。

先看原始的实现代码：

case class WlanHint(
    mac: String,
    signalStrength: Option[Int],
    age: Option[Int],
    channel: Option[Int],
    signalToNoiseRatio: Option[Int]
)
val builder = WifiAccessPoint.WifiAccessPointBuilder().MacAddress(wlanHint.mac)
val b       = wlanHint.signalStrength.map(signalStrength => builder.SignalStrength(signalStrength)).getOrElse(builder)
val b2      = wlanHint.age.map(age => b.Age(age)).getOrElse(b)
val b3      = wlanHint.channel.map(channel => b2.Channel(channel)).getOrElse(b2)
val b4      = wlanHint.signalToNoiseRatio.map(signalToNoiseRatio => b3.SignalToNoiseRatio(signalToNoiseRatio)).getOrElse(b3)
b4.createWifiAccessPoint()

下面给出几种更优雅的优化方案：

方案一：用Option.fold替代map+getOrElse #

Option的fold方法可以直接处理Some和None两种情况，避免重复写getOrElse，让代码更连贯：

case class WlanHint(
    mac: String,
    signalStrength: Option[Int],
    age: Option[Int],
    channel: Option[Int],
    signalToNoiseRatio: Option[Int]
)

val finalBuilder = WifiAccessPoint.WifiAccessPointBuilder()
  .MacAddress(wlanHint.mac)
  // fold参数：None时返回当前builder，Some时调用对应Builder方法
  .signalStrength.fold(_)(_.SignalStrength)
  .age.fold(_)(_.Age)
  .channel.fold(_)(_.Channel)
  .signalToNoiseRatio.fold(_)(_.SignalToNoiseRatio)

finalBuilder.createWifiAccessPoint()

方案二：封装隐式类增强Builder #

通过隐式类给Java Builder添加Scala风格的扩展方法，让调用语义更清晰，同时复用逻辑：

case class WlanHint(
    mac: String,
    signalStrength: Option[Int],
    age: Option[Int],
    channel: Option[Int],
    signalToNoiseRatio: Option[Int]
)

// 定义隐式类，封装Option参数的处理逻辑
implicit class WifiBuilderOps(builder: WifiAccessPoint.WifiAccessPointBuilder) {
  def withSignalStrength(ss: Option[Int]): WifiAccessPoint.WifiAccessPointBuilder =
    ss.fold(builder)(builder.SignalStrength)
  def withAge(age: Option[Int]): WifiAccessPoint.WifiAccessPointBuilder =
    age.fold(builder)(builder.Age)
  def withChannel(channel: Option[Int]): WifiAccessPoint.WifiAccessPointBuilder =
    channel.fold(builder)(builder.Channel)
  def withSignalToNoiseRatio(snr: Option[Int]): WifiAccessPoint.WifiAccessPointBuilder =
    snr.fold(builder)(builder.SignalToNoiseRatio)
}

// 使用扩展方法链式调用
val finalBuilder = WifiAccessPoint.WifiAccessPointBuilder()
  .MacAddress(wlanHint.mac)
  .withSignalStrength(wlanHint.signalStrength)
  .withAge(wlanHint.age)
  .withChannel(wlanHint.channel)
  .withSignalToNoiseRatio(wlanHint.signalToNoiseRatio)

finalBuilder.createWifiAccessPoint()

方案三：用管道操作符实现无中间变量链式调用 #

如果你的项目支持管道操作符（Scala 2.13+可直接用|>，也可以自定义），可以彻底消除中间变量，让流程更直观：

case class WlanHint(
    mac: String,
    signalStrength: Option[Int],
    age: Option[Int],
    channel: Option[Int],
    signalToNoiseRatio: Option[Int]
)

// 自定义管道操作符（Scala 2.13+可省略此步骤）
implicit class PipeOps[A](a: A) {
  def |>[B](f: A => B): B = f(a)
}

// 链式处理整个Builder流程
WifiAccessPoint.WifiAccessPointBuilder()
  .MacAddress(wlanHint.mac)
  |> (b => wlanHint.signalStrength.fold(b)(b.SignalStrength))
  |> (b => wlanHint.age.fold(b)(b.Age))
  |> (b => wlanHint.channel.fold(b)(b.Channel))
  |> (b => wlanHint.signalToNoiseRatio.fold(b)(b.SignalToNoiseRatio))
  |> (_.createWifiAccessPoint())

这些方案都能有效减少冗余代码，让逻辑更清晰，符合Scala的函数式编程风格。

内容的提问来源于stack exchange，提问作者Chris W.