动态重启更换端口

原文：https://mp.weixin.qq.com/s/Hz0gStUXe40FNiuY7rudhA

一种简单办法是，新代码先用其他端口启动，启动完毕后，更改nginx的转发地址，nginx重启非常快，这样就避免了大量的用户访问失败，最后终止老进程就可以。

新思路：

1. 判断端口是否占用
2. 占用则先通过其他端口启动
3. 等待启动完毕后终止老进程
4. 重新创建容器实例并且关联DispatcherServlet

@SpringBootApplication()
@EnableScheduling
public class WebMainApplication {
    public static void main(String[] args) {
        String[] newArgs = args.clone();
        int defaultPort = 8088;
        boolean needChangePort = false;
        if (isPortInUse(defaultPort)) {
            newArgs = new String[args.length + 1];
            System.arraycopy(args, 0, newArgs, 0, args.length);
            newArgs[newArgs.length - 1] = "--server.port=9090";
            needChangePort = true;
        }
        ConfigurableApplicationContext run = SpringApplication.run(WebMainApplication.class, newArgs);
        if (needChangePort) {
            String command = String.format("lsof -i :%d | grep LISTEN | awk '{print $2}' | xargs kill -9", defaultPort);
            try {
                Runtime.getRuntime().exec(new String[]{"sh", "-c", command}).waitFor();
                while (isPortInUse(defaultPort)) {
                }
                ServletWebServerFactory webServerFactory = getWebServerFactory(run);
                ((TomcatServletWebServerFactory) webServerFactory).setPort(defaultPort);
                WebServer webServer = webServerFactory.getWebServer(invokeSelfInitialize(((ServletWebServerApplicationContext) run)));
                webServer.start();

                ((ServletWebServerApplicationContext) run).getWebServer().stop();
            } catch (IOException | InterruptedException ignored) {
            }
        }

    }

    private static ServletContextInitializer invokeSelfInitialize(ServletWebServerApplicationContext context) {
        try {
            Method method = ServletWebServerApplicationContext.class.getDeclaredMethod("getSelfInitializer");
            method.setAccessible(true);
            return (ServletContextInitializer) method.invoke(context);
        } catch (Throwable e) {
            throw new RuntimeException(e);
        }

    }

    private static boolean isPortInUse(int port) {
        try (ServerSocket serverSocket = new ServerSocket(port)) {
            return false;
        } catch (IOException e) {
            return true;
        }
    }

    protected static Collection<ServletContextInitializer> getServletContextInitializerBeans(ConfigurableApplicationContext context) {
        return new ServletContextInitializerBeans(context.getBeanFactory());
    }


    private static ServletWebServerFactory getWebServerFactory(ConfigurableApplicationContext context) {
        String[] beanNames = context.getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class);

        return context.getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
    }

}