通过Flume将本地文件导入Kafka

业务场景

外部设备定期会向本地目录里面写入文本文件，文本内容每行都是以竖线分割，例如

2|235|872|6|460078003|0|||02000bda||
2|235|852|3|460078004|0|||02000bda||
1|235|772|1|460078005|0|||02000bda||

需要通过flume将文件内容导入到kafka中，并指定源文件的第5列的值作为kafka每条消息的key

Flume完整配置

agent.sources = r1
agent.channels = c1
agent.sinks = s1

agent.sources.r1.type = spooldir
agent.sources.r1.spoolDir = /tmp/flume

agent.sources.r1.interceptors = i1
agent.sources.r1.interceptors.i1.type = regex_extractor
agent.sources.r1.interceptors.i1.regex = .*\\|.*\\|.*\\|.*\\|(.*)\\|.*\\|.*\\|.*\\|.*\\|.*\\|.*
agent.sources.r1.interceptors.i1.serializers = s1
agent.sources.r1.interceptors.i1.serializers.s1.name = key

agent.sinks.s1.type = org.apache.flume.sink.kafka.KafkaSink
agent.sinks.s1.topic = test
agent.sinks.s1.brokerList = host1:6667
agent.sinks.s1.requiredAcks = 1
agent.sinks.s1.batchSize = 20

agent.channels.c1.type = memory
agent.channels.c1.capacity = 1000

agent.sinks.s1.channel = c1
agent.sources.r1.channels = c1

配置说明

实现此功能的关键是使用了flume的正则过滤器(regex_extractor)，下面就详细说明一下这个过滤器是如何工作的。

这里使用了正则表达式的组的概念，也就是说在regex中定义的组，每个组匹配的值作为header中的value，而此value的key为s1.name对应的名字。

以下代码是模拟Flume正则过滤器的实现:

    Pattern regex = Pattern.compile("(.*)\\|.*\\|.*\\|(.*)\\|.*\\|.*\\|.*\\|.*\\|.*\\|.*\\|.*");
        
    Matcher matcher = regex.matcher("999|235|872|888|460077171338003|0|||02000bda||");
        
    if (matcher.find()) {
        for (int group = 0, count = matcher.groupCount(); group < count; group++) {
            int groupIndex = group + 1;

            System.out.println(matcher.group(groupIndex));
        }
    }

返回结果是

999
888

可见首先找到所有组的值，然后对应serializers配置，再由serializers.s1.name找到对应的key。

例如是下面这样的配置，而且原数据中有一行999|235|872|888|460077171338003|0|||02000bda||，那么在header中会有两个键值对，key1->999, key2->888

agent.sources.r1.interceptors.i1.regex = .(.*)\\|.*\\|.*\\|(.*)\\|.*\\|.*\\|.*\\|.*\\|.*\\|.*\\|.*
agent.sources.r1.interceptors.i1.serializers = s1 s2
agent.sources.r1.interceptors.i1.serializers.s1.name = key1
agent.sources.r1.interceptors.i1.serializers.s2.name = key2

源码分析

  public Event intercept(Event event) {
    Matcher matcher = regex.matcher(
        new String(event.getBody(), Charsets.UTF_8));//event.getBody()为消息体
    Map headers = event.getHeaders();
    if (matcher.find()) {
      for (int group = 0, count = matcher.groupCount(); group < count; group++) {
        int groupIndex = group + 1;
        if (groupIndex > serializers.size()) {
          if (logger.isDebugEnabled()) {
            logger.debug("Skipping group {} to {} due to missing serializer",
                group, count);
          }
          break;
        }
        NameAndSerializer serializer = serializers.get(group);
        if (logger.isDebugEnabled()) {
          logger.debug("Serializing {} using {}", serializer.headerName,
              serializer.serializer);
        }
        headers.put(serializer.headerName, //serializers.xxx.name定义的值
            serializer.serializer.serialize(matcher.group(groupIndex)));//matcher.group(groupIndex)为根据组匹配到的值
      }
    }
    return event;
  }