fix: Provide correct mime type for javascript and css

The correct mimetype for javascript is a requirement when loading javascript modules#

Author: Artur-

aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/servlet/AwsServletContext.java

@@ -167,7 +167,12 @@ public String getMimeType(String s) {
         if (mimeTypes == null) {
             mimeTypes = new MimetypesFileTypeMap();
         }
-
+        if (s.endsWith(".css")) {
+                return "text/css";
+        }
+        if (s.endsWith(".js")) {
+                return "application/javascript";
+        }
         // TODO: The getContentType method of the MimetypesFileTypeMap returns application/octet-stream
         // instead of null when the type cannot be found. We should replace with an implementation that
         // loads the System mime types ($JAVA_HOME/lib/mime.types

aws-serverless-java-container-core/src/test/java/com/amazonaws/serverless/proxy/internal/servlet/AwsServletContextTest.java

@@ -65,6 +65,13 @@ void getMimeType_mimeTypeOfCorrectFile_expectMime() {
         mimeType = ctx.getMimeType("file://" + tmpFilePath);
         assertEquals("text/plain", mimeType);
     }
+    @Test
+    void getMimeType_mimeTypeOfJavascript_expectApplicationJavascript() {
+        String tmpFilePath = TMP_DIR + "some.js";
+        AwsServletContext ctx = new AwsServletContext(null);
+        String mimeType = ctx.getMimeType(tmpFilePath);
+        assertEquals("application/javascript", mimeType);
+    }
 
     @Test
     void getMimeType_unknownExtension_expectAppOctetStream() {