This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Framework 6.1.12! |
Filters
You can register a client filter (ExchangeFilterFunction
) through the WebClient.Builder
in order to intercept and modify requests, as the following example shows:
-
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()
This can be used for cross-cutting concerns, such as authentication. The following example uses a filter for basic authentication through a static factory method:
-
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()
Filters can be added or removed by mutating an existing WebClient
instance, resulting
in a new WebClient
instance that does not affect the original one. For example:
-
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
is a thin facade around the chain of filters followed by an
ExchangeFunction
. It provides a workflow to make requests, to encode to and from higher
level objects, and it helps to ensure that response content is always consumed.
When filters handle the response in some way, extra care must be taken to always consume
its content or to otherwise propagate it downstream to the WebClient
which will ensure
the same. Below is a filter that handles the UNAUTHORIZED
status code but ensures that
any response content, whether expected or not, is released:
-
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)
}
}
}
}
The example below demonstrates how to use the ExchangeFilterFunction
interface to create
a custom filter class that helps with computing a Content-Length
header for PUT
and POST
multipart/form-data
requests using buffering.
-
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))
}
}
}
}