Fix MediaType lookup for ResourceHttpRequestHandler

As of 4.3 ResourceHttpRequestHandler delegates to the configured
ContentNegotiationManager, or one created internally, to look up
the media type for are resource.

This commit ensures the internally created ContentNegotiationManager is
correctly injected with the ServletContext through which it can perform
lookups as before.

Also the ServletPathContentNegotiationStrategy now checks the
ServletContext first and then delegates to its parent the
PathContentNegotiationStrategy and not vice versa. This is
consistent with how handleNoMatch (also in the same class) works
and also matches how ResourceHttpRequestHandler worked before 4.3.

Issue: SPR-14368

spring-webmvc/src/test/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandlerTests.java

@@ -281,6 +281,34 @@ public class ResourceHttpRequestHandlerTests {
 		assertEquals("h1 { color:red; }", this.response.getContentAsString());
 	}
 
+	@Test // SPR-14368
+	public void getResourceWithMediaTypeResolvedThroughServletContext() throws Exception {
+		MockServletContext servletContext = new MockServletContext() {
+
+			@Override
+			public String getMimeType(String filePath) {
+				return "foo/bar";
+			}
+
+			@Override
+			public String getVirtualServerName() {
+				return null;
+			}
+		};
+
+		List<Resource> paths = Collections.singletonList(new ClassPathResource("test/", getClass()));
+		this.handler = new ResourceHttpRequestHandler();
+		this.handler.setServletContext(servletContext);
+		this.handler.setLocations(paths);
+		this.handler.afterPropertiesSet();
+
+		this.request.setAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE, "foo.css");
+		this.handler.handleRequest(this.request, this.response);
+
+		assertEquals("foo/bar", this.response.getContentType());
+		assertEquals("h1 { color:red; }", this.response.getContentAsString());
+	}
+
 	@Test
 	public void invalidPath() throws Exception {
 		for (HttpMethod method : HttpMethod.values()) {