学一遍根本记不住，那就再学一遍

public static void test_nettyFuture() {
    NioEventLoopGroup group = new NioEventLoopGroup();

    log.info("开始提交任务");
    Future<String> future = group.next().submit(() -> {

        log.info("执行异步任务...");
        try {
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        log.info("异步任务执行完成...");
        return "ok";
    });

    log.info("任务提交结束");

    future.addListener(new GenericFutureListener<Future<String>>() {
        @Override
        public void operationComplete(Future<String> future) throws Exception {
            String s = (String) future.get();
            log.info("监听任务完成回调.......{}", s);
        }
    });

    log.info("任务添加监听结束");
}

public static void test_nettyPromise() {

    NioEventLoopGroup group = new NioEventLoopGroup(10);

    // 指定谁去通知回调方法, 即哪1个线程去调用operationComplete方法
    DefaultPromise<String> promise = new DefaultPromise<>(group.next());

    log.info("提交任务开始");

    group.next().submit(() -> {
        try {

            log.info("开始执行异步任务...");

            TimeUnit.SECONDS.sleep(5);

            promise.setSuccess("ojdk");

            log.info("异步任务还须再执行会儿...");
            TimeUnit.SECONDS.sleep(5);
            log.info("异步任务执行完毕...");

            return "ok";

        } catch (Exception e) {

            log.info("异步任务执行发生异常...");
            promise.setFailure(e);

            return "ok";
        }
    });

    log.info("提交任务结束");

    log.info("添加回调开始");
    promise.addListener(new GenericFutureListener<Future<String>>() {
        @Override
        public void operationComplete(Future<String> future) throws Exception {
            log.info("回调获取到异步结果开始");
            String result = future.get();
            log.info("回调获取到异步结果: {}", result);
        }
    });
    log.info("添加回调结束");


}