为什么在 Kafka 集群未运行的情况下创建主题时 AdminClient 不会失败？

Question

Why don't I get an error message when I run the following producer code and Kafka is not even running?

I would expect the createTopics method to throw an exception, but it doesn't happen. Why?

final Properties properties = new Properties();
properties.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
properties.put(AdminClientConfig.REQUEST_TIMEOUT_MS_CONFIG, "1000");

AdminClient adminClient = AdminClient.create(properties);
NewTopic newTopic = new NewTopic("events", 1, (short) 1);
adminClient.createTopics(Arrays.asList(newTopic));
adminClient.close();

Answer 1

The method createTopics returns a CreateTopicsResult with KafkaFutures as values. As you are currently not blocking your code for this action to be finished (using get ) and not catching any Exception, your code will just run fine without any notification that the broker is not available.

The following code will throw an ExecutionException when your broker is not available:

final Properties properties = new Properties();
properties.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
properties.put(AdminClientConfig.REQUEST_TIMEOUT_MS_CONFIG, "1000");
properties.put(AdminClientConfig.DEFAULT_API_TIMEOUT_MS_CONFIG, "5000");

AdminClient adminClient = AdminClient.create(properties);
NewTopic newTopic = new NewTopic("events-test", 1, (short) 1);
CreateTopicsResult topicResult = adminClient.createTopics(Arrays.asList(newTopic));
KafkaFuture<Void> resultFuture = topicResult.all();
try {
    resultFuture.get();
} catch (InterruptedException e) {
    e.printStackTrace();
} catch (ExecutionException e) {
    e.printStackTrace();
}
adminClient.close();

I tested it using Kafka client 2.5.0 and here is the Excpetion:

java.util.concurrent.ExecutionException: org.apache.kafka.common.errors.TimeoutException: Call(callName=createTopics, deadlineMs=1601136227182) timed out at 1601136227183 after 1 attempt(s)
    at org.apache.kafka.common.internals.KafkaFutureImpl.wrapAndThrow(KafkaFutureImpl.java:45)
    at org.apache.kafka.common.internals.KafkaFutureImpl.access$000(KafkaFutureImpl.java:32)
    at org.apache.kafka.common.internals.KafkaFutureImpl$SingleWaiter.await(KafkaFutureImpl.java:89)
    at org.apache.kafka.common.internals.KafkaFutureImpl.get(KafkaFutureImpl.java:260)
    at org.michael.big.data.kafka.java.BasicAdminClient.main(BasicAdminClient.java:27)
Caused by: org.apache.kafka.common.errors.TimeoutException: Call(callName=createTopics, deadlineMs=1601136227182) timed out at 1601136227183 after 1 attempt(s)
Caused by: org.apache.kafka.common.errors.TimeoutException: Timed out waiting for a node assignment.

Be aware that the class Admin (the super class of AdminClient ) is annotated as Evolving and might be changed in future releases.