目前Kafka并没有提供直接的工具来帮助我们获取某个topic的当前总消息数，需要我们自行写程序来实现。下列代码可以实现这一功能，特此记录一下：
/**
* 获取某个topic的当前消息数
* Java 8+ only
*
* @param topic
* @param brokerList
* @return
*/
public static long totalMessageCount(String topic, String brokerList) {
Properties props = new Properties();
props.put("bootstrap.servers", brokerList);
props.put("group.id", "test-group");
props.put("enable.auto.commit", "false");
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
try (KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props)) {
List<TopicPartition> tps = Optional.ofNullable(consumer.partitionsFor(topic))
.orElse(Collections.emptyList())
.stream()
.map(info -> new TopicPartition(info.topic(), info.partition()))
.collect(Collectors.toList());
Map<TopicPartition, Long> beginOffsets = consumer.beginningOffsets(tps);
Map<TopicPartition, Long> endOffsets = consumer.endOffsets(tps);
return tps.stream().mapToLong(tp -> endOffsets.get(tp) - beginOffsets.get(tp)).sum();
}
}