code: private Certificate[] getCertificates(File container, String entry)
          throws IOException {
          if (container.isDirectory()) {
              return null;
          }
          JarFile jarFile = (JarFile) jarFiles.get(container);
          if (jarFile == null) {
              return null;
          }
          JarEntry ent = jarFile.getJarEntry(entry);
          return ent == null ? null : ent.getCertificates();
      }
docs: Get the certificates for a given jar entry, if it is indeed a jar.
  
  @param container the File from which to read the entry
  @param entry the entry of which the certificates are requested
  
  @return the entry's certificates or null is the container is
  not a jar or it has no certificates.
  
  @exception IOException if the manifest cannot be read.