用于Scala.Option的Spring RequestParam格式化程序 [英] Spring RequestParam formatter for Scala.Option

问题描述

我们在Scala应用程序中使用Spring MVC，我想弄清楚如何解包Scala Option，以便可以使用@RequestParam正确转换它们.我认为该解决方案可能与格式化程序SPI ，但是由于Option可以包含任意数量的值(我希望Spring正常处理，就像转换后的值根本不是Option).从本质上讲，我几乎想在正常转换发生后将值的附加转换应用为Option包装.

We are using Spring MVC in our Scala application and I would like to figure out how to unwrap Scala Option's so they can be properly converted using @RequestParam. I think the solution may have something to do with the Formatter SPI, but I am unsure how to get this to work nicely given that Option's can contain any number of values (which I'd want Spring to handle normally, as if the converted value were not an Option at all). In essence, I'd almost want to apply an additional conversion of a value to be Option wrapped after normal conversion takes place.

例如，给出以下代码:

@RequestMapping(method = Array(GET), value = Array("/test"))
def test(@RequestParam("foo") foo: Option[String]): String

url /test应该导致foo参数获得None的值，而url /test?foo=bar应该导致foo参数获得Some("bar")的值(/test?foo可以结果为空字符串或None.

The url /test should result in the foo parameter getting a value of None, while the url /test?foo=bar should result in the foo parameter getting a value of Some("bar") (/test?foo could result in either an empty String, or None).

推荐答案

我们通过创建一个AnyRef到Option[AnyRef]转换器并将其添加到Spring MVC的ConversionService:

We managed to solve this by creating an AnyRef to Option[AnyRef] converter and adding it to Spring MVC's ConversionService:

import org.springframework.beans.factory.annotation.{Autowired, Qualifier}
import org.springframework.core.convert.converter.ConditionalGenericConverter
import org.springframework.core.convert.converter.GenericConverter.ConvertiblePair
import org.springframework.core.convert.{ConversionService, TypeDescriptor}
import org.springframework.stereotype.Component

import scala.collection.convert.WrapAsJava

/**
 * Base functionality for option conversion.
 */
trait OptionConverter extends ConditionalGenericConverter with WrapAsJava {
  @Autowired
  @Qualifier("mvcConversionService")
  var conversionService: ConversionService = _
}

/**
 * Converts `AnyRef` to `Option[AnyRef]`.
 * See implemented methods for descriptions.
 */
@Component
class AnyRefToOptionConverter extends OptionConverter {
  override def convert(source: Any, sourceType: TypeDescriptor, targetType: TypeDescriptor): AnyRef = {
    Option(source).map(s => conversionService.convert(s, sourceType, new Conversions.GenericTypeDescriptor(targetType)))
  }

  override def getConvertibleTypes: java.util.Set[ConvertiblePair] = Set(
    new ConvertiblePair(classOf[AnyRef], classOf[Option[_]])
  )

  override def matches(sourceType: TypeDescriptor, targetType: TypeDescriptor): Boolean = {
    Option(targetType.getResolvableType).forall(resolvableType =>
      conversionService.canConvert(sourceType, new Conversions.GenericTypeDescriptor(targetType))
    )
  }
}

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