我调用API的producer写发送消息，但是kafka控制台提示创建topic成功，却没有消息？

public void sendMessage(){

  Properties props = new Properties();
  props.put("bootstrap.servers", "192.168.31.96:9092");
  props.put("acks", "all");
  props.put("retries", 0);
  props.put("batch.size", 16384);
  props.put("linger.ms", 1);
  props.put("buffer.memory", 33554432);
  props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
  props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

  KafkaProducer<String,String> producer = new KafkaProducer<>(props);

  for (int i = 0; i <10 ; i++) {
  String mesg = Integer.toString(i);
  ProducerRecord<String, String> records = new      ProducerRecord<String,String>("test4",mesg);
  producer.send(records);
  }
  producer.close();
}