code: public void writeLoaderClasses() throws IOException {
          URL loaderJar = getClass().getClassLoader().getResource(NESTED_LOADER_JAR);
          JarInputStream inputStream = new JarInputStream(
                  new BufferedInputStream(loaderJar.openStream()));
          JarEntry entry;
          while ((entry = inputStream.getNextJarEntry()) != null) {
              if (entry.getName().endsWith(".class")) {
                  writeEntry(entry, new InputStreamEntryWriter(inputStream, false));
              }
          }
          inputStream.close();
      }
docs: Write the required spring-boot-loader classes to the JAR.
  
  @throws IOException if the classes cannot be written