Spring throws HttpMediaTypeNotAcceptableException inexplicably

Question

I have my Spring app configured to use a GET parameter for content negotiation. Code is Kotlin but would work the same in Java.

Config:

override fun configureContentNegotiation(configurer: ContentNegotiationConfigurer) {
        configurer.favorParameter(true)
            .parameterName("format")
            .ignoreAcceptHeader(false)
            .defaultContentType(MediaType.APPLICATION_JSON)
            .mediaType("text/plain", MediaType.TEXT_PLAIN)
            .mediaType("application/json", MediaType.APPLICATION_JSON)
            .mediaType("application/rdf+xml", MediaType("application", "rdf+xml"))
    }

And the following controller methods:

@GetMapping("/test", produces=["text/plain"])
fun testText() : String {
    return "Hello"
}

@GetMapping("/test", produces=["application/json"])
fun testJson() : Map<String, String> {
    return mapOf("hello" to "world")
}

@GetMapping("/test", produces=["application/rdf+xml"])
fun testRdf(response: HttpServletResponse) {
    // dummy response, to demonstrate using output stream.
    response.setContentType("application/rdf+xml")
    response.outputStream.write("dummy data".toByteArray())
    response.outputStream.close()
}

testRdf returns void and uses an output stream to send body data back.

The following works just fine:

• http://localhost:8080/test?format=text/plain gives me the plain text
• http://localhost:8080/test?format=application/json gives me the JSON

But http://localhost:8080/test?format=application/rdf+xml gives me an HTTP 406 and the logs say

org.apache.tomcat.util.http.Parameters   : Start processing with input [format=application/rdf+xml]
o.s.web.servlet.DispatcherServlet        : GET "/test?format=application/rdf+xml", parameters={masked}
.w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation]
o.s.web.servlet.DispatcherServlet        : Completed 406 NOT_ACCEPTABLE

A debugger shows that it doesn't even call my function.

(To prove that the testRdf handler does what's expected, I made the path unique and removed the produces annotation - it works fine outside content negotiation and returns the body as expected.)

As far as I can tell I have indicated that my method is the right handler for that content type, and I have registered the content type correctly.

Why does Spring not consider that my handler meets the content negotiation request?

Answer 1

I found the answer. The parameter characters that needed to be URL encoded, so this works fine:

http://localhost:8080/test?format=application%2Frdf%2Bxml