# Can't access Kafka from a Java app. What may be the problem? **URL:** \ **Category:** Java Clients\ **Created:** [7 September 2023 19:03 UTC](https://forum.confluent.io/t/cant-access-kafka-from-a-java-app-what-may-be-the-problem/8645 "2023-09-07T19:03:03Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Nad.Chel](https://avatars.discourse-cdn.com/v4/letter/n/3be4f8/32.png) [@Nad.Chel](https://forum.confluent.io/u/Nad.Chel)\ **Post date:** [7 September 2023 19:03 UTC](https://forum.confluent.io/t/cant-access-kafka-from-a-java-app-what-may-be-the-problem/8645/1 "2023-09-07T19:03:03Z")
I managed to successfully set up Zookeeper and Kafka servers, and CLI pub/sub operations work fine: ```auto nadchel@LAPTOP-CKP86E2O:/usr/local/kafka/bin$ ./kafka-console-producer.sh --broker-list localhost:9092 --topic test SLF4J: Class path contains multiple SLF4J bindings. SLF4J: Found binding in [jar:file:/usr/local/kafka/tools/build/dependant-libs-2.13.10/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/usr/local/kafka/trogdor/build/dependant-libs-2.13.10/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/usr/local/kafka/connect/runtime/build/dependant-libs/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/usr/local/kafka/connect/mirror/build/dependant-libs/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation. SLF4J: Actual binding is of type [org.slf4j.impl.Reload4jLoggerFactory] >Another message >Yet another message >^C nadchel@LAPTOP-CKP86E2O:/usr/local/kafka/bin$ ./kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic test --from-beginning SLF4J: Class path contains multiple SLF4J bindings. SLF4J: Found binding in [jar:file:/usr/local/kafka/tools/build/dependant-libs-2.13.10/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/usr/local/kafka/trogdor/build/dependant-libs-2.13.10/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/usr/local/kafka/connect/runtime/build/dependant-libs/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [jar:file:/usr/local/kafka/connect/mirror/build/dependant-libs/slf4j-reload4j-1.7.36.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation. SLF4J: Actual binding is of type [org.slf4j.impl.Reload4jLoggerFactory] Another message Yet another message ^CProcessed a total of 2 messages ``` However, when I try to perform similar operations from a simple Java app, it can’t connect. Here’s the app code: ```java package org.example.demos.kafka; import org.apache.kafka.clients.producer.KafkaProducer; import org.apache.kafka.clients.producer.ProducerRecord; import java.util.Properties; public class ProducerMicroservice { private static final String TOPIC_NAME = "my-topic"; private static final String BOOTSTRAP_SERVERS = "localhost:9092"; public static void main(String[] args) { // Configure Kafka producer Properties props = new Properties(); props.put("bootstrap.servers", BOOTSTRAP_SERVERS); props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer"); props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer"); KafkaProducer producer = new KafkaProducer<>(props); // Generate and send messages for (int i = 0; i < 10; i++) { String message = "Message " + i; ProducerRecord record = new ProducerRecord<>(TOPIC_NAME, message); producer.send(record); } // Close the producer producer.close(); } } ``` ```java package org.example.demos.kafka; import org.apache.kafka.clients.consumer.Consumer; import org.apache.kafka.clients.consumer.ConsumerRecords; import org.apache.kafka.clients.consumer.KafkaConsumer; import java.time.Duration; import java.util.Collections; import java.util.Properties; public class ConsumerMicroservice { private static final String TOPIC_NAME = "my-topic"; private static final String BOOTSTRAP_SERVERS = "localhost:9092"; public static void main(String[] args) { // Configure Kafka consumer Properties props = new Properties(); props.put("bootstrap.servers", BOOTSTRAP_SERVERS); props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer"); props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer"); props.put("group.id", "my-group"); try (Consumer consumer = new KafkaConsumer<>(props)) { // Subscribe to the topic and start consuming messages consumer.subscribe(Collections.singleton(TOPIC_NAME)); while (true) { ConsumerRecords records = consumer.poll(Duration.ofMillis(100)); records.forEach(record -> { System.out.println("Received message: " + record.value()); }); } } } } ``` A snippet from a producer log: ```auto ---- 07 сент. 2023 21:47:49,390 DEBUG [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Connection with localhost/127.0.0.1 (channelId=-1) disconnected java.net.ConnectException: Connection refused: no further information at sun.nio.ch.Net.pollConnect(Native Method) ~[?:?] at sun.nio.ch.Net.pollConnectNow(Net.java:672) ~[?:?] at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:946) ~[?:?] at org.apache.kafka.common.network.PlaintextTransportLayer.finishConnect(PlaintextTransportLayer.java:50) ~[kafka-clients-3.5.1.jar:?] at org.apache.kafka.common.network.KafkaChannel.finishConnect(KafkaChannel.java:224) ~[kafka-clients-3.5.1.jar:?] at org.apache.kafka.common.network.Selector.pollSelectionKeys(Selector.java:526) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.common.network.Selector.poll(Selector.java:481) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:571) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.NetworkClientUtils.isReady(NetworkClientUtils.java:42) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.NetworkClientUtils.awaitReady(NetworkClientUtils.java:64) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.awaitNodeReady(Sender.java:534) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.maybeSendAndPollTransactionalRequest(Sender.java:455) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.runOnce(Sender.java:316) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:243) [kafka-clients-3.5.1.jar:?] at java.lang.Thread.run(Thread.java:833) [?:?] ---- 07 сент. 2023 21:47:49,390 INFO [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Node -1 disconnected. ---- 07 сент. 2023 21:47:49,390 WARN [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available. ---- 07 сент. 2023 21:47:49,390 WARN [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Bootstrap broker localhost:9092 (id: -1 rack: null) disconnected ---- 07 сент. 2023 21:47:49,391 DEBUG [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Disconnect from localhost:9092 (id: -1 rack: null) while trying to send request InitProducerIdRequestData(transactionalId=null, transactionTimeoutMs=2147483647, producerId=-1, producerEpoch=-1). Going to back off and retry. java.io.IOException: Connection to localhost:9092 (id: -1 rack: null) failed. at org.apache.kafka.clients.NetworkClientUtils.awaitReady(NetworkClientUtils.java:70) ~[kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.awaitNodeReady(Sender.java:534) ~[kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.maybeSendAndPollTransactionalRequest(Sender.java:455) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.runOnce(Sender.java:316) [kafka-clients-3.5.1.jar:?] at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:243) [kafka-clients-3.5.1.jar:?] at java.lang.Thread.run(Thread.java:833) [?:?] ---- 07 сент. 2023 21:47:49,492 DEBUG [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Enqueuing transactional request InitProducerIdRequestData(transactionalId=null, transactionTimeoutMs=2147483647, producerId=-1, producerEpoch=-1) ---- 07 сент. 2023 21:47:49,492 DEBUG [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Enqueuing transactional request InitProducerIdRequestData(transactionalId=null, transactionTimeoutMs=2147483647, producerId=-1, producerEpoch=-1) ---- 07 сент. 2023 21:47:49,492 DEBUG [kafka-producer-network-thread | producer-1] : [Producer clientId=producer-1] Give up sending metadata request since no node is available ``` I made sure that: 1. Kafka versions are compatible (both are 3.5.1) 2. I specified these properties in the `server.properties` file: ```auto listeners=PLAINTEXT://localhost:9092 advertised.listeners=PLAINTEXT://localhost:9092 ``` It’s all run on the same machine (a laptop) What may be the problem? ---
**Author:** ![OneCricketeer](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.confluent.io/onecricketeer/32/1551_2.png) [@OneCricketeer](https://forum.confluent.io/u/OneCricketeer)\ **Post date:** [18 September 2023 06:10 UTC](https://forum.confluent.io/t/cant-access-kafka-from-a-java-app-what-may-be-the-problem/8645/2 "2023-09-18T06:10:04Z")
Based on the error, Kafka is not running, therefore the network connection is not being made