Fix issue in message conversion

This change ensures that when the Accept and the Producible media types
are equally specific, we use the one from the Accept header, which may
for example carry a different charset.

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java

@@ -193,7 +193,7 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 	 */
 	private MediaType getMostSpecificMediaType(MediaType acceptType, MediaType produceType) {
 		produceType = produceType.copyQualityValue(acceptType);
-		return MediaType.SPECIFICITY_COMPARATOR.compare(acceptType, produceType) < 0 ? acceptType : produceType;
+		return MediaType.SPECIFICITY_COMPARATOR.compare(acceptType, produceType) <= 0 ? acceptType : produceType;
 	}
 
 }

org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/mvc/method/annotation/RequestResponseBodyMethodProcessorTests.java

@@ -315,6 +315,21 @@ public class RequestResponseBodyMethodProcessorTests {
 		assertEquals("Foo", servletResponse.getContentAsString());
 	}
 
+	@Test
+	public void handleReturnValueStringAcceptCharset() throws Exception {
+		this.servletRequest.addHeader("Accept", "text/plain;charset=UTF-8");
+
+		List<HttpMessageConverter<?>> converters = new ArrayList<HttpMessageConverter<?>>();
+		converters.add(new ByteArrayHttpMessageConverter());
+		converters.add(new StringHttpMessageConverter());
+		RequestResponseBodyMethodProcessor processor = new RequestResponseBodyMethodProcessor(converters);
+
+		processor.writeWithMessageConverters("Foo", returnTypeString, webRequest);
+
+		assertEquals("text/plain;charset=UTF-8", servletResponse.getHeader("Content-Type"));
+	}
+
+
 	@ResponseBody
 	public String handle1(@RequestBody String s, int i) {
 		return s;