code: public static void main(String[] args) throws Exception {
          int zkPort;
          boolean secureZK = false;
          String zkKeyStore;
          String zkKeyStorePasswd = null;
          String zkTrustStore = null;
          try {
              zkPort = Integer.parseInt(System.getProperty(PROPERTY_ZK_PORT));
              secureZK = Boolean.parseBoolean(System.getProperty(PROPERTY_SECURE_ZK, "false"));
              zkKeyStore = System.getProperty(PROPERTY_ZK_KEY_STORE);
              zkKeyStorePasswd = System.getProperty(PROPERTY_ZK_KEY_STORE_PASSWORD);
              zkTrustStore = System.getProperty(PROPERTY_ZK_TRUST_STORE);
          } catch (Exception ex) {
              System.out.println(String.format("Invalid or missing arguments (via system properties). Expected: %s(int). (%s)",
                      PROPERTY_ZK_PORT, ex.getMessage()));
              System.exit(-1);
              return;
          }
  
          ZooKeeperServiceRunner runner = new ZooKeeperServiceRunner(zkPort, secureZK,
                  zkKeyStore, zkKeyStorePasswd, zkTrustStore);
          runner.initialize();
          runner.start();
          Thread.sleep(Long.MAX_VALUE);
      }
docs: Main method that can be used to start ZooKeeper out-of-process using BookKeeperServiceRunner.
  This is used when invoking this class via ProcessStarter.
  
  @param args Args.
  @throws Exception If an error occurred.