code: public synchronized JarFile getNestedJarFile(JarEntryData sourceEntry)
              throws IOException {
          try {
              if (sourceEntry.nestedJar == null) {
                  sourceEntry.nestedJar = createJarFileFromEntry(sourceEntry);
              }
              return sourceEntry.nestedJar;
          } catch (IOException ex) {
              throw new IOException(
                      "Unable to open nested jar file '" + sourceEntry.getName() + "'", ex);
          }
      }
docs: Return a nested {@link JarFile} loaded from the specified entry.
  
  @param sourceEntry the zip entry
  @return a {@link JarFile} for the entry
  @throws IOException if the nested jar file cannot be read