code: @Override
      public String getContentType() {
          if (url.getFile().endsWith("!/")) {
              // the type for jar file itself is always "x-java/jar"
              return "x-java/jar";
          }
          String cType = null;
          String entryName = getEntryName();
  
          if (entryName != null) {
              // if there is an Jar Entry, get the content type from the name
              cType = guessContentTypeFromName(entryName);
          } else {
              try {
                  connect();
                  cType = jarFileURLConnection.getContentType();
              } catch (IOException ioe) {
                  // Ignore
              }
          }
          if (cType == null) {
              cType = "content/unknown";
          }
          return cType;
      }
docs: Returns the content type of the resource. For jar file itself
  "x-java/jar" should be returned, for jar entries the content type of the
  entry should be returned. Returns non-null results ("content/unknown" for
  unknown types).
  
  @return the content type