code: private int doLaunch(Container container, Path containerWorkDir) throws Exception {
          Map<String, String> environment = container.getLaunchContext().getEnvironment();
          EnvironmentUtils.putAll(environment);
  
          Set<URL> additionalClassPathUrls = this.filterAndBuildUserClasspath(container);
  
          ExecJavaCliParser javaCliParser = this.createExecCommandParser(containerWorkDir.toString());
  
          UserGroupInformation.setLoginUser(null);
          try {
              // create Isolated Class Loader for each container and set it as context
              // class loader
              URLClassLoader containerCl =
                      new URLClassLoader(additionalClassPathUrls.toArray(additionalClassPathUrls.toArray(new URL[]{})), null);
              Thread.currentThread().setContextClassLoader(containerCl);
              String containerLauncher = javaCliParser.getMain();
  
  
              Class<?> containerClass = Class.forName(containerLauncher, true, containerCl);
              Method mainMethod = containerClass.getMethod("main", new Class[] { String[].class });
              mainMethod.setAccessible(true);
              String[] arguments = javaCliParser.getMainArguments();
  
              this.doLaunchContainer(containerClass, mainMethod, arguments);
  
          }
          catch (Exception e) {
              logger.error("Failed to launch container " + container, e);
              container.handle(new ContainerDiagnosticsUpdateEvent(container.getContainerId(), e.getMessage()));
              return -1;
          }
          finally {
              logger.info("Removing symlinks");
              this.cleanUp();
          }
          return 0;
      }
docs: Will launch containers within the same JVM as this Container Executor. It
  will do so by: - extracting Container's class name and program arguments
  from the launch script (e.g., launch_container.sh) - Creating an isolated
  ClassLoader for each container - Calling doLaunchContainer(..) method to
  launch Container