Kafka 2.6卡住,Topic not present in metadata
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想自己耍耍Kafka，简单装好后，运行个简单的demo，结果直接卡住不动了，但使用命令行发消息是正常的。我的Kafka版本为2.6，demo代码为：
package top.jlice;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerRecord;
import java.util.Properties;
public class MyProducer {
public static void main(String[] args) {
Properties properties = new Properties();
properties.put("bootstrap.servers", "localhost:9092");
properties.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
properties.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");
KafkaProducer<String, String> producer = new KafkaProducer<>(properties);
for (int i = 0; i < 10; i++) {
producer.send(new ProducerRecord<String, String>("test", "jlice.top-" + i));
}
producer.close();
}
}
通过debug发现，在waitOnMetadata方法里的下面这行卡住的：
metadata.awaitUpdate(version, remainingWaitMs);
尽管KafkaProducer.send是异步的，还是可能出现阻塞的。KafkaProducer.send方法返回一个Future<RecordMetadata>，为了取得结果，可以使用get方法：
try {
for (int i = 0; i < 10; i++) {
producer.send(new ProducerRecord<String, String>("test", "jlice.top-" + i)).get();
}
} catch (Exception e) {
e.printStackTrace();
}
Kafka默认的超时时间是60s，这样修改后在60s后出现报错：
java.util.concurrent.ExecutionException: org.apache.kafka.common.errors.TimeoutException: Topic test not present in metadata after 60000 ms.
at org.apache.kafka.clients.producer.KafkaProducer$FutureFailure.<init>(KafkaProducer.java:1314)
at org.apache.kafka.clients.producer.KafkaProducer.doSend(KafkaProducer.java:970)
at org.apache.kafka.clients.producer.KafkaProducer.send(KafkaProducer.java:870)
at org.apache.kafka.clients.producer.KafkaProducer.send(KafkaProducer.java:758)
at top.jlice.MyProducer.main(MyProducer.java:17)
Caused by: org.apache.kafka.common.errors.TimeoutException: Topic test not present in metadata after 60000 ms.
当然，还可以为properties设置一个更短的超时时间，比如1s，这样会更快出现报错→_→
properties.put("max.block.ms", 1000);
在pom.xml里点进kafka的版本查看kafka-client-2.6.0.pom，发现了下面的依赖配置：
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.10.2</version>
<scope>provided</scope>
</dependency>
注意到scope为provided，maven官网该项的解释是：
this is much like compile, but indicates you expect the JDK or a container to provide the dependency at runtime.
心想，可能是因为缺少了这个依赖项吧，于是在pom.xml里添加该依赖项：
<dependencies>
<dependency>
<groupId>org.apache.kafka</groupId>
<artifactId>kafka-clients</artifactId>
<version>2.6.0</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.10.2</version>
</dependency>
</dependencies>
然后，就正常了。