bigbang489 edited a comment on issue #6960:
URL: https://github.com/apache/pulsar/issues/6960#issuecomment-632557593
This is my code
`package com.test;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import org.apache.pulsar.client.api.AuthenticationFactory;
import org.apache.pulsar.client.api.ClientBuilder;
import org.apache.pulsar.client.api.Consumer;
import org.apache.pulsar.client.api.DeadLetterPolicy;
import org.apache.pulsar.client.api.Message;
import org.apache.pulsar.client.api.MessageListener;
import org.apache.pulsar.client.api.Producer;
import org.apache.pulsar.client.api.PulsarClient;
import org.apache.pulsar.client.api.PulsarClientException;
import org.apache.pulsar.client.api.SubscriptionType;
public class App {
static Executor executor = Executors.newFixedThreadPool(3);
public static void main(String[] args) throws InterruptedException,
PulsarClientException {
startConsumer("my-topic", false);
startConsumer("my-topic", false);
startConsumer("my-topic", false);
startConsumer("DLQ", true); // This consumer is for dead letter
Thread.sleep(2000);
publish(String.valueOf(System.currentTimeMillis()), "my-topic");
}
static void startConsumer(String topic, boolean ack) {
executor.execute(()-> {
try {
subscribe(topic, ack);
} catch (PulsarClientException e) {
e.printStackTrace();
}
});
}
static Consumer<byte[]> subscribe(String topic, boolean ack) throws
PulsarClientException {
ClientBuilder cb = PulsarClient.builder();
cb.serviceUrl("pulsar://pulsar:6650");
cb.authentication(AuthenticationFactory.token("*************"));
PulsarClient client = cb.build();
@SuppressWarnings("serial")
Consumer<byte[]> consumer = client.newConsumer()
.subscriptionName("test")
.subscriptionType(SubscriptionType.Shared)
.topic(topic)
.ackTimeout(12, TimeUnit.SECONDS)
.messageListener(new MessageListener<byte[]>() {
@Override
public void received(Consumer<byte[]> consumer,
Message<byte[]> msg) {
System.out.println("\r\nReceive
messaged: '" + new String(msg.getData()) + "' from topic: " +
msg.getTopicName());
try {
if(ack) {
consumer.acknowledge(msg);
}
} catch (PulsarClientException e) {
e.printStackTrace();
}
}
})
.deadLetterPolicy(DeadLetterPolicy.builder()
.deadLetterTopic("DLQ")
.maxRedeliverCount(2)
.build())
.subscribe();
System.out.println("\r\nStarted a consumer...");
return consumer;
}
static void publish(String message, String topic) throws
PulsarClientException {
ClientBuilder cb = PulsarClient.builder();
cb.serviceUrl("pulsar://pulsar:6650");
cb.authentication(AuthenticationFactory.token("***************"));
PulsarClient client = cb.build();
Producer<byte[]> producer =
client.newProducer().topic(topic).create();
try {
System.out.println("\r\nSent message: " +
producer.send(message.getBytes()));
}
finally {
producer.close();
}
}
}
`
POM file:
`<dependency>
<groupId>org.apache.pulsar</groupId>
<artifactId>pulsar-client</artifactId>
<version>2.5.1</version>
</dependency>
<dependency>
<groupId>org.apache.pulsar</groupId>
<artifactId>pulsar-client-api</artifactId>
<version>2.5.1</version>
</dependency>`
**The result**
Receive messaged: '1590133963111' from topic:
persistent://public/default/my-topic
Receive messaged: '1590133963111' from topic:
persistent://public/default/my-topic
Receive messaged: '1590133963111' from topic:
persistent://public/default/my-topic
**Receive messaged: '1590133963111' from topic:
persistent://public/default/DLQ**
Receive messaged: '1590133963111' from topic:
persistent://public/default/my-topic
**Receive messaged: '1590133963111' from topic:
persistent://public/default/DLQ**
As you see, the message is sent to DLQ twice.
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