如何覆盖子类中的macwire注入

Posted 2021-05-04

Play web框架允许注入一个“过滤器”列表，对请求进行常见处理（gzip，cors，logging等）

package play.api

trait BuiltInComponents {
  ...
  lazy val httpFilters: Seq[EssentialFilter] = Nil
  <stuff that uses httpFilters>
  ...
}

我想有一套共同的过滤器（以及其他东西）。

package example

import play.api.BuildInComponents

trait MyCommonComponents extends BuiltInComponents {
    ...
    override lazy val filters = Seq(
      wire[Filter1],
      wire[Filter2],
      wire[Filter3]
    )
    ...
}

哪个子类可以使用

package example.foo

import example.MyCommonComponents

trait MyFooComponents extends MyCommonComponents {
    ...
}

或者通过子类添加

package example.bar

import example.MyCommonComponents

trait MyBarComponents extends MyCommonComponents {
    ...
    override lazy val filters = super.filters :+ wire[Filter4]
    ...
}

---

我尝试过的事情

1. 上面的代码。不能使用lazy val的super。
2. 将httpFilters改为def。由于BuiltInComponents，需要是一个稳定的值
3. 添加lazy val httpFilters = filters和def filters: Seq[EssentialFilter] = ...然后适当地覆盖filters。 Macwire抱怨模棱两可的类型。

我该怎么做才能实现可选的附加过滤器列表？

答案

我可能没有得到你的场景，但简单的错误

import com.softwaremill.macwire._
import play.api.BuiltInComponents
import play.api.mvc.{EssentialAction, EssentialFilter}

class Filter1 extends EssentialFilter {
  override def apply(next: EssentialAction) = next
}

class Filter2 extends EssentialFilter {
  override def apply(next: EssentialAction) = next
}

class Filter3 extends EssentialFilter {
  override def apply(next: EssentialAction) = next
}

trait MyCommonComponents extends BuiltInComponents {

  protected lazy val baseFilters: Seq[EssentialFilter] = Seq(
    wire[Filter1],
    wire[Filter2],
  )

  override def httpFilters = baseFilters
}


trait MyFooComponents extends MyCommonComponents {

  protected lazy val fooFilters = baseFilters :+ wire[Filter3]

  override def httpFilters = fooFilters
}

或这个

trait MyBarComponents extends MyCommonComponents {

  private lazy val barFilters = Seq[EssentialFilter](wire[Filter3])

  override def httpFilters = super.httpFilters ++ barFilters
}

你为什么要覆盖你的lazy val而不是基本的httpFilters，它们似乎被设计为被覆盖。