SpringBoot implements dynamic port switching black magic

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@SpringBootApplication()
public class BootMainApplication {
    public static void main(String[] args) {
        // Default port settings        int defaultPort = 8080;
        // Alternative port settings        int alternativePort = 9090;
        // Check whether the default port has been occupied        boolean isPortOccupied = isPortInUse(defaultPort);

        // Dynamic port allocation        int portToUse = isPortOccupied ? alternativePort : defaultPort;
        // Create Spring Boot application instance        SpringApplication app = new SpringApplication();
        // Set port configuration        (("", portToUse));
        // Run the application and get the context        ConfigurableApplicationContext context = (args);

        // If the default port is occupied, try to switch back to the default port        if (isPortOccupied) {
            switchToDefaultPort(context, defaultPort, portToUse);
        }
    }

    /**
      * Switch to default port
      *
      * When the default port is occupied by other processes, this method tries to release the port and starts a new web server instance to bind to the default port
      * At the same time, it will stop the current web server instance
      *
      * @param context Current application context, used to access the web server factory and stop the current web server
      * @param defaultPort default port number, the target port you want to switch to
      * @param currentPort The port number currently being used by the web server
      */
    private static void switchToDefaultPort(ConfigurableApplicationContext context, int defaultPort, int currentPort) {
        try {
            // Release the default port            terminateProcessUsingPort(defaultPort);

            // Wait for the port to be released            while (isPortInUse(defaultPort)) {
                (100);
            }

            // Start a new container to bind the default port            ServletWebServerFactory webServerFactory = getWebServerFactory(context);
            ((TomcatServletWebServerFactory) webServerFactory).setPort(defaultPort);

            WebServer newServer = (getServletContextInitializers(context));
            ();

            // Stop the current container            ((ServletWebServerApplicationContext) context).getWebServer().stop();
        } catch (Exception e) {
            ();
        }
    }

    /**
      * Check whether the specified port is in use
      *
      * @param port The port number to be checked
      * @return Return true if the port is in use; otherwise return false
      */
    private static boolean isPortInUse(int port) {
        try (ServerSocket serverSocket = new ServerSocket(port)) {
            // If you can successfully create a ServerSocket instance, it means that the port is available and return false            return false;
        } catch (IOException e) {
            // If an IOException is thrown when creating a ServerSocket instance, it means that the port has been occupied and returns true            return true;
        }
    }

    /**
      * Terminate the process using the specified port
      *
      * @param port The port number that needs to be released
      * @throws IOException If an error occurs when executing the command
      * @throws InterruptedException if thread is interrupted
      */
    private static void terminateProcessUsingPort(int port) throws IOException, InterruptedException {
        // Build a command to terminate a process using the specified port        String command = ("lsof -i :%d | grep LISTEN | awk '{print $2}' | xargs kill -9", port);
        // Execute the command and wait for the command to be executed        ().exec(new String[]{"sh", "-c", command}).waitFor();
    }

    /**
      * Get the ServletContextInitializer instance
      * This method is used to transfer all ServletContextInitializerBeans instances in Spring application context
      * Convert to implementation of ServletContextInitializer interface to initialize ServletContext at application startup
      *
      * @param context Spring's application context, used to get BeanFactory
      * @return Return an instance that implements the ServletContextInitializer interface
      */
    private static ServletContextInitializer getServletContextInitializers(ConfigurableApplicationContext context) {
        // Create a ServletContextInitializerBeans instance using BeanFactory in ApplicationContext        // Here we return ServletContextInitializerBeans as the implementation class of ServletContextInitializer        // ServletContextInitializerBeans will be responsible for collecting all implementations of ServletContextInitializer in the application context        // and call their onStartup methods in turn when the application starts to initialize the ServletContext        return (ServletContextInitializer) new ServletContextInitializerBeans(());
    }

    /**
      * Get the Servlet Web Server Factory
      *
      * @param context Configurable application context for obtaining bean factories
      * @return ServletWebServerFactory instance, used to configure and create web servers
      */
    private static ServletWebServerFactory getWebServerFactory(ConfigurableApplicationContext context) {
        // Get the Bean factory from the application context and get the ServletWebServerFactory instance from it        return ().getBean();
    }
}

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@RestController()
@RequestMapping("port/")
public class TestPortController {
    @GetMapping("test")
    public String test() {
        return "artisan-old";
    }
}