过滤器

您可以通过 WebClient.Builder 注册一个客户端过滤器 (ExchangeFilterFunction)，以便拦截和修改请求，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。以下示例通过静态工厂方法使用过滤器进行基本身份验证：

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()

可以通过修改现有的 WebClient 实例来添加或删除过滤器，从而生成一个新的 WebClient 实例，该实例不会影响原始实例。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 是过滤器链和 ExchangeFunction 的一个薄门面。它提供了一个工作流来发出请求、在高级对象之间进行编码和解码，并有助于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，始终消费其内容或将其向下游传播到 WebClient，这将确保相同。下面是一个处理 UNAUTHORIZED 状态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)
			}
		}
	}
}

下面的示例演示如何使用 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
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))
				}
		}
	}
}