Provide control over fallback charset to use in WebClientResponseException

[j3r0lin]

Affects: 5.3.6

---

Web client should throw an WebClientResponseException when http response status is 4xx, which is created by clientResponse.createException(), if the error response is JSON string, the media type should be application/json, that should decode http response body using UTF-8 encoding by default, but current using ISO-8859-1 for all media types. it causes body field in the generated exception contains malformed characters.

spring-framework/spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientResponse.java

Lines 209 to 213 in e4a5d2a

	HttpRequest request = this.requestSupplier.get();
	Charset charset = headers().contentType()
	.map(MimeType::getCharset)
	.orElse(StandardCharsets.ISO_8859_1);
	int statusCode = rawStatusCode();

[rstoyanchev]

Indeed, assuming ISO_8859_1 as a default fallback is unfortunate.

[rstoyanchev]

I made change where you can pass the fallback Charset to use into the getResponseBodyAsString method of WebClientResponseException. I'm afraid that's as far as we can go in a 5.3.7 release. Perhaps in a future major or minor version we can change the default. For extra context, indeed a JSON response should be UTF-8 but following a similar change in other areas, we had plenty of feedback about JSON responses that aren't UTF-8 beyond a client's control.