基于Kotlin的Spring WebFlux响应式异常处理器实现遇错求助

问题背景 #

参照Spring官方文档编写Spring WebFlux异常处理器时出现错误，原始代码如下：

import org.springframework.boot.autoconfigure.web.WebProperties
import org.springframework.boot.autoconfigure.web.reactive.error.AbstractErrorWebExceptionHandler
import org.springframework.boot.web.reactive.error.ErrorAttributes
import org.springframework.context.ApplicationContext
import org.springframework.http.HttpStatus
import org.springframework.http.MediaType
import org.springframework.stereotype.Component
import org.springframework.web.reactive.function.server.RouterFunction
import org.springframework.web.reactive.function.server.RouterFunctions
import org.springframework.web.reactive.function.server.ServerRequest
import org.springframework.web.reactive.function.server.ServerResponse
import reactor.core.publisher.Mono

@Component
class MyErrorWebExceptionHandler(errorAttributes: ErrorAttributes?, resources: WebProperties.Resources?,
    applicationContext: ApplicationContext?) : AbstractErrorWebExceptionHandler(errorAttributes, resources, applicationContext) {

    override fun getRoutingFunction(errorAttributes: ErrorAttributes): RouterFunction<ServerResponse> {
        return RouterFunctions.route(this::acceptsXml, this::handleErrorAsXml)
    }

    private fun acceptsXml(request: ServerRequest): Boolean {
        return request.headers().accept().contains(MediaType.APPLICATION_XML)
    }

    fun handleErrorAsXml(request: ServerRequest?): Mono<ServerResponse> {
        val builder = ServerResponse.status(HttpStatus.INTERNAL_SERVER_ERROR)
        // ... additional builder calls
        return builder.build()
    }

}

核心修正点 #

• 构造函数参数与初始化修正
  Spring Boot 2.6+版本中，WebProperties.Resources需通过WebProperties实例获取，且构造参数应使用非空类型（Spring依赖注入会确保实例存在）。同时必须配置消息读写器，避免序列化异常：

  constructor(
      errorAttributes: ErrorAttributes,
      webProperties: WebProperties,
      applicationContext: ApplicationContext
  ) : super(errorAttributes, webProperties.resources, applicationContext) {
      setMessageWriters(ServerCodecConfigurer.create().writers)
      setMessageReaders(ServerCodecConfigurer.create().readers)
  }
  

• 处理方法参数与逻辑完善
  handleErrorAsXml的ServerRequest参数不应为可空类型，且需从ErrorAttributes中获取异常详情生成有意义的响应：

  private fun handleErrorAsXml(request: ServerRequest): Mono<ServerResponse> {
      val error = getError(request)
      val status = determineStatus(error) ?: HttpStatus.INTERNAL_SERVER_ERROR
      
      val xmlResponse = """
          <error>
              <status>${status.value()}</status>
              <error>${status.reasonPhrase}</error>
              <message>${error.message ?: "Unknown error"}</message>
          </error>
      """.trimIndent()
      
      return ServerResponse.status(status)
          .contentType(MediaType.APPLICATION_XML)
          .bodyValue(xmlResponse)
  }
  

• 覆盖多响应场景
  建议添加默认JSON响应处理，覆盖所有请求格式：

  override fun getRoutingFunction(errorAttributes: ErrorAttributes): RouterFunction<ServerResponse> {
      return RouterFunctions.route(this::acceptsXml, this::handleErrorAsXml)
          .andRoute(RequestPredicates.all(), this::handleErrorAsJson)
  }
  
  private fun handleErrorAsJson(request: ServerRequest): Mono<ServerResponse> {
      val error = getError(request)
      val status = determineStatus(error) ?: HttpStatus.INTERNAL_SERVER_ERROR
      
      val errorDetails = mapOf(
          "status" to status.value(),
          "error" to status.reasonPhrase,
          "message" to (error.message ?: "Unknown error")
      )
      
      return ServerResponse.status(status)
          .contentType(MediaType.APPLICATION_JSON)
          .bodyValue(errorDetails)
  }
  

完整修正代码 #

import org.springframework.boot.autoconfigure.web.WebProperties
import org.springframework.boot.autoconfigure.web.reactive.error.AbstractErrorWebExceptionHandler
import org.springframework.boot.web.reactive.error.ErrorAttributes
import org.springframework.context.ApplicationContext
import org.springframework.http.HttpStatus
import org.springframework.http.MediaType
import org.springframework.stereotype.Component
import org.springframework.web.reactive.function.server.RequestPredicates
import org.springframework.web.reactive.function.server.RouterFunction
import org.springframework.web.reactive.function.server.RouterFunctions
import org.springframework.web.reactive.function.server.ServerRequest
import org.springframework.web.reactive.function.server.ServerResponse
import org.springframework.web.reactive.function.server.ServerCodecConfigurer
import reactor.core.publisher.Mono

@Component
class MyErrorWebExceptionHandler(
    errorAttributes: ErrorAttributes,
    webProperties: WebProperties,
    applicationContext: ApplicationContext
) : AbstractErrorWebExceptionHandler(errorAttributes, webProperties.resources, applicationContext) {

    init {
        setMessageWriters(ServerCodecConfigurer.create().writers)
        setMessageReaders(ServerCodecConfigurer.create().readers)
    }

    override fun getRoutingFunction(errorAttributes: ErrorAttributes): RouterFunction<ServerResponse> {
        return RouterFunctions.route(this::acceptsXml, this::handleErrorAsXml)
            .andRoute(RequestPredicates.all(), this::handleErrorAsJson)
    }

    private fun acceptsXml(request: ServerRequest): Boolean {
        return request.headers().accept().contains(MediaType.APPLICATION_XML)
    }

    private fun handleErrorAsXml(request: ServerRequest): Mono<ServerResponse> {
        val error = getError(request)
        val status = determineStatus(error) ?: HttpStatus.INTERNAL_SERVER_ERROR
        
        val xmlResponse = """
            <error>
                <status>${status.value()}</status>
                <error>${status.reasonPhrase}</error>
                <message>${error.message ?: "Unknown error"}</message>
            </error>
        """.trimIndent()
        
        return ServerResponse.status(status)
            .contentType(MediaType.APPLICATION_XML)
            .bodyValue(xmlResponse)
    }

    private fun handleErrorAsJson(request: ServerRequest): Mono<ServerResponse> {
        val error = getError(request)
        val status = determineStatus(error) ?: HttpStatus.INTERNAL_SERVER_ERROR
        
        val errorDetails = mapOf(
            "status" to status.value(),
            "error" to status.reasonPhrase,
            "message" to (error.message ?: "Unknown error")
        )
        
        return ServerResponse.status(status)
            .contentType(MediaType.APPLICATION_JSON)
            .bodyValue(errorDetails)
    }
}

内容的提问来源于stack exchange，提问作者Saher Al-Sous