过滤器

ChatGPT-4o 中英对照 Filters

您可以通过 WebClient.Builder 注册一个客户端过滤器（ExchangeFilterFunction）来拦截和修改请求，如下例所示：

Java

WebClient client = WebClient.builder()
        .filter((request, next) -> {

            ClientRequest filtered = ClientRequest.from(request)
                    .header("foo", "bar")
                    .build();

            return next.exchange(filtered);
        })
        .build();

java

Kotlin

val client = WebClient.builder()
        .filter { request, next ->

            val filtered = ClientRequest.from(request)
                    .header("foo", "bar")
                    .build()

            next.exchange(filtered)
        }
        .build()

kotlin

这可以用于横切关注点，例如身份验证。以下示例通过静态工厂方法使用过滤器进行基本身份验证：

Java

import static org.springframework.web.reactive.function.client.ExchangeFilterFunctions.basicAuthentication;

WebClient client = WebClient.builder()
        .filter(basicAuthentication("user", "password"))
        .build();

java

Kotlin

import org.springframework.web.reactive.function.client.ExchangeFilterFunctions.basicAuthentication

val client = WebClient.builder()
        .filter(basicAuthentication("user", "password"))
        .build()

kotlin

可以通过修改现有的 WebClient 实例来添加或移除过滤器，从而生成一个新的 WebClient 实例，而不会影响原始实例。例如：

Java

import static org.springframework.web.reactive.function.client.ExchangeFilterFunctions.basicAuthentication;

WebClient client = webClient.mutate()
        .filters(filterList -> {
            filterList.add(0, basicAuthentication("user", "password"));
        })
        .build();

java

Kotlin

val client = webClient.mutate()
        .filters { it.add(0, basicAuthentication("user", "password")) }
        .build()

kotlin

WebClient 是一个围绕过滤器链以及 ExchangeFunction 的薄封装。它提供了一种工作流程来发起请求，进行高层对象的编码和解码，并帮助确保响应内容始终被消费。当过滤器以某种方式处理响应时，必须格外小心，以始终消费其内容或将其传播到下游的 WebClient，后者将确保同样的事情。下面是一个处理 UNAUTHORIZED 状态码的过滤器，但确保无论响应内容是否预期，都会被释放：

Java

public ExchangeFilterFunction renewTokenFilter() {
    return (request, next) -> next.exchange(request).flatMap(response -> {
        if (response.statusCode().value() == HttpStatus.UNAUTHORIZED.value()) {
            return response.releaseBody()
                    .then(renewToken())
                    .flatMap(token -> {
                        ClientRequest newRequest = ClientRequest.from(request).build();
                        return next.exchange(newRequest);
                    });
        } else {
            return Mono.just(response);
        }
    });
}

java

Kotlin

fun renewTokenFilter(): ExchangeFilterFunction? {
    return ExchangeFilterFunction { request: ClientRequest?, next: ExchangeFunction ->
        next.exchange(request!!).flatMap { response: ClientResponse ->
            if (response.statusCode().value() == HttpStatus.UNAUTHORIZED.value()) {
                return@flatMap response.releaseBody()
                        .then(renewToken())
                        .flatMap { token: String? ->
                            val newRequest = ClientRequest.from(request).build()
                            next.exchange(newRequest)
                        }
            } else {
                return@flatMap Mono.just(response)
            }
        }
    }
}

kotlin

下面的示例演示了如何使用 ExchangeFilterFunction 接口创建一个自定义过滤器类，该类通过缓冲来帮助计算 PUT 和 POST multipart/form-data 请求的 Content-Length 头。

Java

public class MultipartExchangeFilterFunction implements ExchangeFilterFunction {

    @Override
    public Mono<ClientResponse> filter(ClientRequest request, ExchangeFunction next) {
        if (MediaType.MULTIPART_FORM_DATA.includes(request.headers().getContentType())
                && (request.method() == HttpMethod.PUT || request.method() == HttpMethod.POST)) {
            return next.exchange(ClientRequest.from(request).body((outputMessage, context) ->
                request.body().insert(new BufferingDecorator(outputMessage), context)).build()
            );
        } else {
            return next.exchange(request);
        }
    }

    private static final class BufferingDecorator extends ClientHttpRequestDecorator {

        private BufferingDecorator(ClientHttpRequest delegate) {
            super(delegate);
        }

        @Override
        public Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {
            return DataBufferUtils.join(body).flatMap(buffer -> {
                getHeaders().setContentLength(buffer.readableByteCount());
                return super.writeWith(Mono.just(buffer));
            });
        }
    }
}

java

Kotlin

class MultipartExchangeFilterFunction : ExchangeFilterFunction {

    override fun filter(request: ClientRequest, next: ExchangeFunction): Mono<ClientResponse> {
        return if (MediaType.MULTIPART_FORM_DATA.includes(request.headers().getContentType())
            && (request.method() == HttpMethod.PUT || request.method() == HttpMethod.POST)) {
            next.exchange(ClientRequest.from(request)
                .body { message, context -> request.body().insert(BufferingDecorator(message), context) }
                .build())
        }
        else {
            next.exchange(request)
        }

    }

    private class BufferingDecorator(delegate: ClientHttpRequest) : ClientHttpRequestDecorator(delegate) {
        override fun writeWith(body: Publisher<out DataBuffer>): Mono<Void> {
            return DataBufferUtils.join(body)
                .flatMap {
                    headers.contentLength = it.readableByteCount().toLong()
                    super.writeWith(Mono.just(it))
                }
        }
    }
}

kotlin