code: private void findJarEntry() throws IOException {
          if (getEntryName() == null) {
              return;
          }
          jarEntry = jarFile.getJarEntry(getEntryName());
          if (jarEntry == null) {
              throw new FileNotFoundException(getEntryName());
          }
      }
docs: Look up the JarEntry of the entry referenced by this {@code
  URLConnection}.