1、需要掌握概念

//同步，异步，异步回调
//MQ消息中间件

例子：工作邮件、微信、QQ
原理：
同步、异步、异步回调

2、代码

public static void main(String[] args) throws Exception {
    //同步，异步，异步回调
    //MQ消息中间件
    //同步
    CompletableFuture<Void> completableFuture1 =
            CompletableFuture.runAsync(()->{
                System.out.println(Thread.currentThread().getName()
                        +"\t CompletableFuture.runAsync");
            });
    completableFuture1.get();

    //异步回调
    CompletableFuture<Integer> completableFuture2=
            CompletableFuture.supplyAsync(()->{
                System.out.println(Thread.currentThread().getName()
                        +"\t CompletableFuture.supplyAsync");
                int i = 10/0;
                return 1024;
            });

    completableFuture2.whenComplete((t, u)->{
        System.out.println("---t="+t);
        System.out.println("---u="+u);
    }).get();
}