Kafka consumer API is not working properly - apache-kafka

Question

I am new to Kafka .i started doing on Kafka i am facing below issue please help me to solve this one thank in advance.
First i am writing producer API it is working fine but while doing Consumer API messages are not display.
My code is like this :
import java.util.Arrays;
import java.util.Properties;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.ConsumerRecord;
public class ConsumerGroup {
public static void main(String[] args) throws Exception {
String topic = "Hello-Kafka";
String group = "myGroup";
Properties props = new Properties();
props.put("bootstrap.servers", "XXX.XX.XX.XX:9092");
props.put("group.id", group);
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(props);
try {
consumer.subscribe(Arrays.asList(topic));
System.out.println("Subscribed to topic " + topic);
ConsumerRecords<String, String> records = consumer.poll(100);
System.out.println("records ::" + records);
System.out.println(records.toString());
for (ConsumerRecord<String, String> record : records) {
System.out.println("Record::" + record.offset());
System.out.println(record.key());
System.out.println(record.value());
}
consumer.commitSync();
} catch (Exception e) {
e.printStackTrace();
} finally {
consumer.commitSync();
consumer.close();
}
}
}
Response ::
Subscribed to topic Hello-Kafka
records ::org.apache.kafka.clients.consumer.ConsumerRecords#76b0bfab
org.apache.kafka.clients.consumer.ConsumerRecords#76b0bfab
here not printing the Offset,key,value
Control is not coming to for (ConsumerRecord record : records) {
that for loop it self please help me.

Answer 1

You are trying to print empty records, hence only records.toString() is printing in your code, which essentially is the name of the class.
I made some changes in your code and got it working. Do have a look if this helps.
public class ConsumerGroup {
public static void main(String[] args) throws Exception {
String topic = "Hello-Kafka";
String group = "myGroup";
Properties props = new Properties();
props.put("bootstrap.servers", "xx.xx.xx.xx:9092");
props.put("group.id", group);
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer<String, String> consumer = new KafkaConsumer<String, String>(props);
try {
consumer.subscribe(Arrays.asList(topic));
System.out.println("Subscribed to topic " + topic);
while(true){
ConsumerRecords<String, String> records = consumer.poll(1000);
if(records.isEmpty()){
}
else{
System.out.println("records ::" + records);
System.out.println(records.toString());
for (ConsumerRecord<String, String> record : records) {
System.out.println("Record::" + record.offset());
System.out.println(record.key());
System.out.println(record.value());
}
consumer.commitSync();
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
consumer.commitSync();
consumer.close();
}
}
}