Jackson message converters and codecs do not respect character encoding in canRead/canWrite

[saimonsez]

Affects: org.springframework:spring-web:5.1.15.RELEASE

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XML webservices seem to be limited to unicode encodings. Using jackson-dataformat-xml 2.9.8 for a webservice which produces "text/xml;charset=ISO-8859-1" outputs utf-8.

The problem might be located in AbstractJackson2HttpMessageConverter:

...
protected void writeInternal(Object object, @Nullable Type type, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
    MediaType contentType = outputMessage.getHeaders().getContentType();
    JsonEncoding encoding = getJsonEncoding(contentType);
    JsonGenerator generator = this.objectMapper.getFactory().createGenerator(outputMessage.getBody(), encoding);
...

JsonEncoding only provides unicode. A workaround would be to override the whole method but it is quite lenghty.

I made a very small reproducer: https://github.com/saimonsez/spring-jackson-xml-encoding-problem

[poutsma]

The underlying issues seems to be that AbstractJackson2HttpMessageConverter and subclasses do not check the media type encoding if asked if they can read or write a given media type. As a result, the converter reports that it can write (for instance) "application/json;charset=ISO-8859-1", but in practice writes the default charset (UTF-8).

As you eluded to Jackson does not support non-unicode encodings and we cannot change that, but we can fix the issue above. This way, you can use a different XML converter (such as the Jaxb2RootElementHttpMessageConverter, which does support non-unicode charsets).

[saimonsez]

Regarding Jacksons support of non-unicode, please also see FasterXML/jackson-dataformat-xml#315.