如何使用 lettuce java 库持续监听 redis 流

Question

我正在尝试侦听 redis 流并在消息到达时对其进行处理。我正在使用异步命令，我希望消息被推送而不是被拉取。所以我认为不需要while循环。但是下面的代码好像不行。

public static void main(String[] args) throws InterruptedException {

    RedisClient redisClient = RedisClient
        .create("redis://localhost:6379/");
    StatefulRedisConnection<String, String> connection
        = redisClient.connect();
    RedisAsyncCommands commands = connection.async();
    commands.xgroupCreate(StreamOffset.latest("my-stream"), "G1", new XGroupCreateArgs());
    commands
        .xreadgroup(Consumer.from("G1", "c1"), StreamOffset.lastConsumed("my-stream"))
        .thenAccept(System.out::println);

    Thread.currentThread().join();
}

它只打印程序启动时流的任何内容，而不打印程序运行时添加的消息。不是应该为每条新添加到流中的消息调用回调吗？

Answer 1

我认为你应该使用 xgroupCreate 方法来创建消费者和组之间的链接，否则你会得到错误。

exception in thread "main" java.util.concurrent.ExecutionException: io.lettuce.core.RedisCommandExecutionException: NOGROUP No such key 'my-stream1' or consumer group 'group1' in XREADGROUP with GROUP option
    at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
    at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1895)
    at com.test.TestList.main(TestList.java:57)
Caused by: io.lettuce.core.RedisCommandExecutionException: NOGROUP No such key 'my-stream1' or consumer group 'group1' in XREADGROUP with GROUP option
    at io.lettuce.core.ExceptionFactory.createExecutionException(ExceptionFactory.java:135)
    at io.lettuce.core.ExceptionFactory.createExecutionException(ExceptionFactory.java:108)
    at io.lettuce.core.protocol.AsyncCommand.completeResult(AsyncCommand.java:120)
    at io.lettuce.core.protocol.AsyncCommand.complete(AsyncCommand.java:111)
    at io.lettuce.core.protocol.CommandHandler.complete(CommandHandler.java:654)
    at io.lettuce.core.protocol.CommandHandler.decode(CommandHandler.java:614)
    at io.lettuce.core.protocol.CommandHandler.channelRead(CommandHandler.java:565)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1422)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:931)
    at io.netty.channel.kqueue.AbstractKQueueStreamChannel$KQueueStreamUnsafe.readReady(AbstractKQueueStreamChannel.java:544)
    at io.netty.channel.kqueue.AbstractKQueueChannel$AbstractKQueueUnsafe.readReady(AbstractKQueueChannel.java:381)
    at io.netty.channel.kqueue.KQueueEventLoop.processReady(KQueueEventLoop.java:211)
    at io.netty.channel.kqueue.KQueueEventLoop.run(KQueueEventLoop.java:289)
    at io.netty.util.concurrent.SingleThreadEventExecutor$6.run(SingleThreadEventExecutor.java:1050)
    at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
    at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
    at java.lang.Thread.run(Thread.java:748)

示例代码如下：

package com.test;

import io.lettuce.core.Consumer;
import io.lettuce.core.RedisClient;
import io.lettuce.core.RedisFuture;
import io.lettuce.core.StreamMessage;
import io.lettuce.core.XGroupCreateArgs;
import io.lettuce.core.XReadArgs.StreamOffset;
import io.lettuce.core.api.StatefulRedisConnection;
import io.lettuce.core.api.async.RedisAsyncCommands;

import java.util.List;
public class TestList {
    public static void main(String[] args) throws Exception {
        RedisClient redisClient = RedisClient.create("redis://localhost:6379/");
        StatefulRedisConnection<String, String> connection = redisClient.connect();
        RedisAsyncCommands commands = connection.async();
        RedisFuture<String> redisFuture = commands.xadd("my-stream1", "test", "1234");
        String redisFutureGet = redisFuture.get();
        System.out.println(redisFutureGet);
        commands.xgroupCreate(StreamOffset.latest("my-stream1"), "group1", new XGroupCreateArgs()); // add a group pointing to the stream
        RedisFuture<List<StreamMessage<String, String>>> messages = commands.xreadgroup(Consumer.from("group1", "my-stream1"),
                StreamOffset.lastConsumed("my-stream1"));
        List<StreamMessage<String, String>> res = messages.get();
        System.out.println(res);
    }
}

Answer 2

我认为 Lettuce 只是用于与 Redis 通信的响应，无论是同步，异步还是流方式。它是一个低级库。所以如果你想要这样的高级功能，使用 spinrg-data 这样的东西：

StreamListener<String, MapRecord<String, String, String>> streamListener = new ExampleStreamListener();

   StreamMessageListenerContainer.StreamMessageListenerContainerOptions<String, MapRecord<String, String, String>> containerOptions = StreamMessageListenerContainer.StreamMessageListenerContainerOptions
                .builder().pollTimeout(Duration.ofMillis(100)).build();

StreamMessageListenerContainer<String, MapRecord<String, String, String>> container = StreamMessageListenerContainer.create(connectionFactory,
                containerOptions);
Subscription subscription = container.receive(StreamOffset.fromStart("key2"), streamListener);
container.start();
//----------------------------------------------------------------

public class ExampleStreamListener implements StreamListener<String, MapRecord<String, String, String>> {

    @Override
    public void onMessage(MapRecord<String, String, String> message) {

        System.out.println("MessageId: " + message.getId());
        System.out.println("Stream: " + message.getStream());
        System.out.println("Body: " + message.getValue());
    }
}

Answer 3

您可以使用 Redis 响应式命令来实现此目的：

RedisReactiveCommands<String, String> commands = connection.reactive();
commands.xgroupCreate(StreamOffset.latest("my-stream"), "G1", new XGroupCreateArgs());
commands
    .xreadgroup(Consumer.from("G1", "c1"), StreamOffset.lastConsumed("my-stream"))
    .subscribe(System.out::println, Throwable::printStackTrace);