Tair (Redis OSS-compatible) oferece suporte ao recurso Redis Pub/Sub. Um cliente publica mensagens em um canal e outros clientes as assinam para recebê-las.
Como o Pub/Sub funciona
As mensagens publicadas pelo Tair (Redis OSS-compatible) não são persistentes e seguem o modelo fire-and-forget. O publicador não verifica a existência de assinantes nem salva mensagens. Os assinantes recebem apenas as mensagens publicadas após a assinatura.
O publicador não exige conexão exclusiva. Você pode usar a mesma conexão para outras operações durante a publicação. No entanto, o assinante precisa de uma conexão exclusiva, pois fica bloqueado aguardando mensagens. Utilize uma conexão ou thread separada para cada assinante.
Exemplos de código
Publicador (cliente de publicação)
package message.kvstore.aliyun.com;
import redis.clients.jedis.Jedis;
public class KVStorePubClient {
private Jedis jedis;
public KVStorePubClient(String host,int port, String password){
jedis = new Jedis(host,port);
// The password of the instance
String authString = jedis.auth(password);
if (!authString.equals("OK"))
{
System.err.println("AUTH Failed: " + authString);
return;
}
}
public void pub(String channel,String message){
System.out.println(" >>> PUBLISH > Channel:"+channel+" > Sent Message:"+message);
jedis.publish(channel, message);
}
public void close(String channel){
System.out.println(" >>> PUBLISH ends > Channel:"+channel+" > Message:quit");
// The publisher stops sending messages by sending a "quit" message.
jedis.publish(channel, "quit");
}
}Assinante (cliente de assinatura)
package message.kvstore.aliyun.com;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPubSub;
public class KVStoreSubClient extends Thread{
private Jedis jedis;
private String channel;
private JedisPubSub listener;
public KVStoreSubClient(String host,int port, String password){
jedis = new Jedis(host,port);
// The password of the instance
String authString = jedis.auth(password);//password
if (!authString.equals("OK"))
{
System.err.println("AUTH Failed: " + authString);
return;
}
}
public void setChannelAndListener(JedisPubSub listener,String channel){
this.listener=listener;
this.channel=channel;
}
private void subscribe(){
if(listener==null || channel==null){
System.err.println("Error:SubClient> listener or channel is null");
}
System.out.println(" >>> SUBSCRIBE > Channel:"+channel);
System.out.println();
// When listening for subscribed messages, the receiver blocks the process until it receives a "quit" message (passive) or actively unsubscribes.
jedis.subscribe(listener, channel);
}
public void unsubscribe(String channel){
System.out.println(" >>> UNSUBSCRIBE > Channel:"+channel);
System.out.println();
listener.unsubscribe(channel);
}
@Override
public void run() {
try{
System.out.println();
System.out.println("----------SUBSCRIBE starts-------");
subscribe();
System.out.println("----------SUBSCRIBE ends-------");
System.out.println();
}catch(Exception e){
e.printStackTrace();
}
}
}Listener de mensagens
package message.kvstore.aliyun.com;
import redis.clients.jedis.JedisPubSub;
public class KVStoreMessageListener extends JedisPubSub{
@Override
public void onMessage(String channel, String message) {
System.out.println(" <<< SUBSCRIBE < Channel:" + channel + " > Received Message:" + message );
System.out.println();
// When the received message is "quit", unsubscribe from the channel (passive).
if(message.equalsIgnoreCase("quit")){
this.unsubscribe(channel);
}
}
@Override
public void onPMessage(String pattern, String channel, String message) {
// TODO Auto-generated method stub
}
@Override
public void onSubscribe(String channel, int subscribedChannels) {
// TODO Auto-generated method stub
}
@Override
public void onUnsubscribe(String channel, int subscribedChannels) {
// TODO Auto-generated method stub
}
@Override
public void onPUnsubscribe(String pattern, int subscribedChannels) {
// TODO Auto-generated method stub
}
@Override
public void onPSubscribe(String pattern, int subscribedChannels) {
// TODO Auto-generated method stub
}
}Programa principal da demonstração
package message.kvstore.aliyun.com;
import java.util.UUID;
import redis.clients.jedis.JedisPubSub;
public class KVStorePubSubTest {
// The connection information of the instance, which can be obtained from the console.
static final String host = "xxxxxxxxxx.m.cnhza.kvstore.aliyuncs.com";
static final int port = 6379;
static final String password="password";// The password.
public static void main(String[] args) throws Exception{
KVStorePubClient pubClient = new KVStorePubClient(host, port,password);
final String channel = "KVStore-Channel-A";
// The publisher starts sending messages. At this point, no one has subscribed, so this message will not be received.
pubClient.pub(channel, "Alibaba Cloud Message 1: (No one has subscribed yet, so this message will not be received)");
// The message subscriber.
KVStoreSubClient subClient = new KVStoreSubClient(host, port,password);
JedisPubSub listener = new KVStoreMessageListener();
subClient.setChannelAndListener(listener, channel);
// The subscriber starts to subscribe.
subClient.start();
// The publisher continues to send messages.
for (int i = 0; i < 5; i++) {
String message=UUID.randomUUID().toString();
pubClient.pub(channel, message);
Thread.sleep(1000);
}
// The subscriber actively unsubscribes.
subClient.unsubscribe(channel);
Thread.sleep(1000);
pubClient.pub(channel, "Alibaba Cloud Message 2: (The subscription is canceled, so this message will not be received)");
// The publisher stops sending messages by sending a "quit" message.
// If there are other subscribers, they will execute the "unsubscribe" operation when they receive "quit" in listener.onMessage().
pubClient.close(channel);
}
}Saída de exemplo
Execute o programa Java com o endpoint e a senha corretos da sua instância Tair (Redis OSS-compatible). Saída esperada:
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:Alibaba Cloud Message 1: (No one has subscribed yet, so this message will not be received)
----------SUBSCRIBE starts-------
>>> SUBSCRIBE > Channel:KVStore-Channel-A
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:0f9c2cee-77c7-4498-89a0-1dc5a2f65889
<<< SUBSCRIBE < Channel:KVStore-Channel-A > Received Message:0f9c2cee-77c7-4498-89a0-1dc5a2f65889
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:ed5924a9-016b-469b-8203-7db63d06f812
<<< SUBSCRIBE < Channel:KVStore-Channel-A > Received Message:ed5924a9-016b-469b-8203-7db63d06f812
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:f1f84e0f-8f35-4362-9567-25716b1531cd
<<< SUBSCRIBE < Channel:KVStore-Channel-A > Received Message:f1f84e0f-8f35-4362-9567-25716b1531cd
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:746bde54-af8f-44d7-8a49-37d1a245d21b
<<< SUBSCRIBE < Channel:KVStore-Channel-A > Received Message:746bde54-af8f-44d7-8a49-37d1a245d21b
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:8ac3b2b8-9906-4f61-8cad-84fc1f15a3ef
<<< SUBSCRIBE < Channel:KVStore-Channel-A > Received Message:8ac3b2b8-9906-4f61-8cad-84fc1f15a3ef
>>> UNSUBSCRIBE > Channel:KVStore-Channel-A
----------SUBSCRIBE ends-------
>>> PUBLISH > Channel:KVStore-Channel-A > Sent Message:Alibaba Cloud Message 2: (The subscription is canceled, so this message will not be received)
>>> PUBLISH ends > Channel:KVStore-Channel-A > Message:quitEste exemplo utiliza um publicador e um assinante. Modifique o código conforme necessário para suportar múltiplos publicadores, assinantes e canais.