java.util.concurrent.Future
io.netty.util.concurrent.Future
io.netty.util.concurrent.Promise

io.netty.util.concurrent.Future extends java.util.concurrent.Future 
io.netty.util.concurrent.Promise extends io.netty.util.concurrent.Future

jdk自带的Future只能同步等待结果。
netty自带的Future能同步等待结果，也可以用异步的方式（如：使用addListener方法设置回调方法）等待结果。
Promise有Future的所有功能，脱离任务独立存在（可以主动创建并赋结果），可作为线程之间传递结果的容器。







import io.netty.channel.EventLoop;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.util.concurrent.DefaultPromise;
import io.netty.util.concurrent.GenericFutureListener;
import io.netty.util.concurrent.Promise;

import java.time.LocalDateTime;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class FutureAndPromiseDemo {
    public static void main(String[] args) throws Exception{

        ExecutorService executor = Executors.newFixedThreadPool(2);
        Future<String> future = executor.submit(new Callable<String>() {
            @Override
            public String call() throws Exception {
                Thread.sleep(1000);
                return "result,"+ LocalDateTime.now();
            }
        });
        System.out.println(future.get());

        // netty future
        NioEventLoopGroup eventExecutors = new NioEventLoopGroup();
        EventLoop eventLoop = eventExecutors.next();
        io.netty.util.concurrent.Future<String> nettyfuture = eventLoop.submit(new Callable<String>() {
            @Override
            public String call() throws Exception {
                Thread.sleep(1000);
                return "netty_future_result_"+LocalDateTime.now();
            }
        });

        nettyfuture.addListener(new GenericFutureListener<io.netty.util.concurrent.Future<? super String>>() {
            @Override
            public void operationComplete(io.netty.util.concurrent.Future<? super String> future) throws Exception {
                // get or getNow
                System.out.println(future.getNow());
            }
        });

        System.out.println(LocalDateTime.now());
        Thread.sleep(2000);

        //  promise
        Promise<String> promise = new DefaultPromise<>(eventLoop);
        new Thread(()->{
            try {
                Thread.sleep(1000);
                promise.setSuccess("netty_promise_result_"+LocalDateTime.now());
            } catch (Exception e) {
                promise.setFailure(e);
            }
        }).start();
        System.out.println(LocalDateTime.now());
        System.out.println(promise.get());
    }
}





https://gitee.com/dyyx/netty-learning-example/blob/master/netty-iot/src/main/java/com/sanshengshui/iot/test/FutureAndPromiseDemo.java