WARN [Producer clientId=console-producer] Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
使用命令行启动生产者：
bin/kafka-console-producer.sh --broker-list localhost:9092 --topic demo #报错信息 WARN [Producer clientId=console-producer] Connection to node -1 (localhost/127.0.0.1:9092) could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
