code: private void loadManifest()
    {
      if (_isManifestRead)
        return;
      
      synchronized (this) {
        if (_isManifestRead)
          return;
  
        try {
          _manifest = _jarPath.getManifest();
          if (_manifest == null)
            return;
  
          Attributes attr = _manifest.getMainAttributes();
          if (attr != null)
            addManifestPackage("", attr);
  
          Map<String,Attributes> entries = _manifest.getEntries();
  
          for (Map.Entry<String,Attributes> entry : entries.entrySet()) {
            String pkg = entry.getKey();
  
            attr = entry.getValue();
            if (attr == null)
              continue;
  
            addManifestPackage(pkg, attr);
          }
        } catch (IOException e) {
          log.log(Level.WARNING, e.toString(), e);
        } finally {
          _isManifestRead = true;
        }
      }
    }
docs: Reads the jar's manifest.