Use null in MockServletContext for unknown mime types

MockServletContext.getMimeTypes now returns null if the Java Activation
Framework returns "application/octet-stream", which is the default
media type it returns if the mime type is unknown. This enforces the
contract for ServletContext.getMimeTypes (return null for uknown mime
types) but does mean "application/octet-stream" cannot be returned.

Issue: SPR-10334

spring-test/src/main/java/org/springframework/mock/web/MockServletContext.java

@@ -242,8 +242,16 @@ public class MockServletContext implements ServletContext {
 		return this.effectiveMinorVersion;
 	}
 
+	/**
+	 * This method uses the Java Activation framework, which returns
+	 * "application/octet-stream" when the mime type is unknown (i.e. it never returns
+	 * {@code null}). In order to maintain the {@link ServletContext#getMimeType(String)
+	 * contract, as of version 3.2.2, this method returns null if the mimeType is
+	 * "application/octet-stream".
+	 */
 	public String getMimeType(String filePath) {
-		return MimeTypeResolver.getMimeType(filePath);
+		String mimeType = MimeTypeResolver.getMimeType(filePath);
+		return ("application/octet-stream".equals(mimeType)) ? null : mimeType;
 	}
 
 	public Set<String> getResourcePaths(String path) {

spring-web/src/test/java/org/springframework/mock/web/test/MockServletContext.java

@@ -45,7 +45,6 @@ import javax.servlet.descriptor.JspConfigDescriptor;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
-
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
@@ -258,9 +257,17 @@ public class MockServletContext implements ServletContext {
 		return this.effectiveMinorVersion;
 	}
 
+	/**
+	 * This method uses the Java Activation framework, which returns
+	 * "application/octet-stream" when the mime type is unknown (i.e. it never returns
+	 * {@code null}). In order to maintain the {@link ServletContext#getMimeType(String)
+	 * contract, as of version 3.2.2, this method returns null if the mimeType is
+	 * "application/octet-stream".
+	 */
 	@Override
 	public String getMimeType(String filePath) {
-		return MimeTypeResolver.getMimeType(filePath);
+		String mimeType = MimeTypeResolver.getMimeType(filePath);
+		return ("application/octet-stream".equals(mimeType)) ? null : mimeType;
 	}
 
 	@Override

spring-web/src/test/java/org/springframework/web/accept/PathExtensionContentNegotiationStrategyTests.java

@@ -74,10 +74,12 @@ public class PathExtensionContentNegotiationStrategyTests {
 		assertEquals(Arrays.asList(new MediaType("application", "vnd.ms-excel")), mediaTypes);
 	}
 
+	// SPR-10334
+
 	@Test
 	public void getMediaTypeFromFilenameNoJaf() {
 
-		this.servletRequest.setRequestURI("test.xls");
+		this.servletRequest.setRequestURI("test.json");
 
 		ServletContext servletContext = this.servletRequest.getServletContext();
 		PathExtensionContentNegotiationStrategy strategy =
@@ -86,7 +88,7 @@ public class PathExtensionContentNegotiationStrategyTests {
 
 		List<MediaType> mediaTypes = strategy.resolveMediaTypes(this.webRequest);
 
-		assertEquals(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM), mediaTypes);
+		assertEquals(Collections.emptyList(), mediaTypes);
 	}
 
 	// SPR-8678