过滤器

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

Java
Kotlin

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

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

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

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

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

			next.exchange(filtered)
		}
		.build()

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

Java
Kotlin

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

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

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

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

可以通过改变现有的WebClient实例来添加或移除过滤器，从而得到一个不影响原始实例的新WebClient实例。例如：

Java
Kotlin

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

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

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

WebClient是围绕过滤器链后跟的ExchangeFunction的薄外观。它提供了一个工作流程来发出请求，对高级对象进行编码和解码，并帮助确保始终消耗响应内容。当过滤器以某种方式处理响应时，必须特别小心始终消耗其内容或以其他方式将其传播到将确保相同的WebClient的下游。以下是一个处理UNAUTHORIZED状态代码但确保释放任何响应内容（无论是否预期）的过滤器：

Java
Kotlin

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);
		}
	});
}

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)
			}
		}
	}
}

以下示例演示如何使用ExchangeFilterFunction接口创建一个自定义过滤器类，用于帮助计算PUT和POST multipart/form-data请求的Content-Length头部，使用缓冲。

Java
Kotlin

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));
            });
        }
    }
}

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))
                }
        }
    }
}