Try defaulContentType for application/octet-stream

AbstractHttpMessageConverter now tries to call getDefaultContentType
with the actual value to be converted to see if that will result in
a more concrete mediat type than application/octet-stream.

Issue: SPR-12894

spring-web/src/main/java/org/springframework/http/converter/AbstractHttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -174,6 +174,10 @@ public abstract class AbstractHttpMessageConverter<T> implements HttpMessageConv
 			if (contentType == null || contentType.isWildcardType() || contentType.isWildcardSubtype()) {
 				contentTypeToUse = getDefaultContentType(t);
 			}
+			else if (MediaType.APPLICATION_OCTET_STREAM.equals(contentType)) {
+				MediaType type = getDefaultContentType(t);
+				contentTypeToUse = (type != null ? type : contentTypeToUse);
+			}
 			if (contentTypeToUse != null) {
 				headers.setContentType(contentTypeToUse);
 			}

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

@@ -30,6 +30,9 @@ import org.junit.Test;
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.aop.target.SingletonTargetSource;
 import org.springframework.core.MethodParameter;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.Resource;
 import org.springframework.http.HttpEntity;
 import org.springframework.http.HttpInputMessage;
 import org.springframework.http.HttpStatus;
@@ -38,6 +41,7 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.http.converter.ByteArrayHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.HttpMessageNotReadableException;
+import org.springframework.http.converter.ResourceHttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
 import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
@@ -49,6 +53,7 @@ import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestMethod;
 import org.springframework.web.bind.annotation.ResponseBody;
 import org.springframework.web.bind.annotation.RestController;
 import org.springframework.web.bind.support.WebDataBinderFactory;
@@ -285,6 +290,24 @@ public class RequestResponseBodyMethodProcessorTests {
 		assertEquals("text/plain;charset=UTF-8", servletResponse.getHeader("Content-Type"));
 	}
 
+	// SPR-12894
+
+	@Test
+	public void handleReturnValueImage() throws Exception {
+		this.servletRequest.addHeader("Accept", "*/*");
+
+		Method method = getClass().getMethod("getImage");
+		MethodParameter returnType = new MethodParameter(method, -1);
+
+		List<HttpMessageConverter<?>> converters = Arrays.asList(new ResourceHttpMessageConverter());
+		RequestResponseBodyMethodProcessor processor = new RequestResponseBodyMethodProcessor(converters);
+
+		ClassPathResource resource = new ClassPathResource("logo.jpg", getClass());
+		processor.writeWithMessageConverters(resource, returnType, this.webRequest);
+
+		assertEquals("image/jpeg", this.servletResponse.getHeader("Content-Type"));
+	}
+
 	@Test
 	public void supportsReturnTypeResponseBodyOnType() throws Exception {
 		Method method = ResponseBodyController.class.getMethod("handle");
@@ -512,6 +535,10 @@ public class RequestResponseBodyMethodProcessorTests {
 		return null;
 	}
 
+	@SuppressWarnings("unused")
+	public Resource getImage() {
+		return null;
+	}
 
 	@SuppressWarnings("unused")
 	private static abstract class MyParameterizedController<DTO extends Identifiable> {