spring - 如何全局处理 Spring WebFlux 中 WebFilter 抛出的错误？

Question

当错误从 WebFilter 链中抛出时，如何在 WebFlux 中全局拦截和处理错误？

很清楚如何处理 Controller 抛出的错误:@ControllerAdvice和@ExceptionHandler帮助很大。

当 WebFilter 组件抛出异常时，此方法不起作用。

在以下配置中，GET/first 和 GET/second 响应有意引发异常抛出。尽管@ExceptionHandler 方法handleFirst、handleSecond 类似，但handleSecond 永远不会被调用。我想这是因为 MyWebFilter 不允许 ServerWebExchange 进入可以应用 GlobalErrorHandlers 方法的阶段。

响应 GET/first:

 HTTP 500 "hello first"                   // expected
 HTTP 500 "hello first"                   // actual

响应 GET/秒:

 HTTP 404 "hello second"                                                         // expected
 HTTP 500 {"path": "/second", "status": 500, "error": "Internal Server Error" }  // actual

---

@RestController
class MyController {

    @GetMapping("/first")
    String first(){
        throw new FirstException("hello first");
    }
}


@Component
class MyWebFilter implements WebFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange swe, WebFilterChain wfc) {
        var path = swe.getRequest().getURI().getPath();
        if (path.contains("second")){
            throw new SecondException("hello second")
        }
    }
}


@ControllerAdvice
class GlobalErrorHandlers {

    @ExceptionHandler(FirstException::class)
    ResponseEntity<String> handleFirst(FirstException ex) {
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(ex.message)
    }

    @ExceptionHandler(SecondException::class)
    ResponseEntity<String> handleSecond(SecondException ex) {
       return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ex.message)
    }
}

Answer 1

需要三个步骤才能完全控制从应用程序端点处理代码抛出的所有异常:

1. 实现org.springframework.boot.web.reactive.error.ErrorWebExceptionHandler
2. 使用 @ControllerAdvice(或仅 @Component)进行注释
3. 将 @Priority 设置为小于 1，以使自定义处理程序在默认处理程序 (WebFluxResponseStatusExceptionHandler) 之前运行

The tricky part is where we get an instance implementing ServerResponse.Context for passing to ServerResponse.writeTo(exchange, context). I did not find the final answer, and comments are welcome. In the internal Spring code they always create a new instance of context for each writeTo invocation, although in all cases (I've manged to find) the context instance is immutable. That is why I ended up using the same ResponseContextInstance for all responses. At the moment no problems detected with this approach.

---

@ControllerAdvice
@Priority(0) /* should go before WebFluxResponseStatusExceptionHandler */
class CustomWebExceptionHandler : ErrorWebExceptionHandler { 

    private val log = logger(CustomWebExceptionHandler::class)

    override fun handle(exchange: ServerWebExchange, ex: Throwable): Mono<Void> {
        log.error("handled ${ex.javaClass.simpleName}", ex)

        val sr = when (ex) {
            is FirstException -> handleFirst(ex) 
            is SecondException -> handleSecond(ex) 
            else -> defaultException(ex)
        }

        return sr.flatMap { it.writeTo(exchange, ResponseContextInstance) }.then()
    }

    private fun handleFirst(ex: FirstException): Mono<ServerResponse> {
        return ServerResponse
                   .status(HttpStatus.INTERNAL_SERVER_ERROR)
                   .bodyValue("first")
    }

    private fun handleSecond(ex: SecondException): Mono<ServerResponse> {
        return ServerResponse.status(HttpStatus.BAD_REQUEST).bodyValue("second")
    }

    private object ResponseContextInstance : ServerResponse.Context {

        val strategies: HandlerStrategies = HandlerStrategies.withDefaults()

        override fun messageWriters(): List<HttpMessageWriter<*>> {
            return strategies.messageWriters()
        }

        override fun viewResolvers(): List<ViewResolver> {
            return strategies.viewResolvers()
        }
    }
}