RegexExtractorInterceptor作为一个Interceptor实现类可以根据一个正则表达式匹配event body来提取字符串，并使用serializers把字符串作为header的值实例：以如下的命令使用execsource收集日志的时候，可以根据文件的名称设置不同的header，进行不同的操作

#!/bin/sh
filename=$1
hostname=`hostname -s`
tail -F $1 | awk -v filename=$filename -v hostname=$hostname '{print filename":"hostname":"$0}'

source的配置：

xxxx.sources.kafka1.interceptors = i1
xxxx.sources.kafka1.interceptors.i1.type = regex_extractor
xxxx.sources.kafka1.interceptors.i1.regex = /apps/logs/(.*?)/
xxxx.sources.kafka1.interceptors.i1.serializers = s1
xxxx.sources.kafka1.interceptors.i1.serializers.s1.name = logtypename
xxxx.sources.kafka1.selector.type = multiplexing
xxxx.sources.kafka1.selector.header = logtypename
xxxx.sources.kafka1.selector.mapping.nginx = nginx-channel

几个参数项：regex 正则表达式

serializers  定义匹配组(正则匹配之后的值作为header的值,比如如果
Event body为1:2:3.4foobar5,regex为(\\d):(\\d):(\\d)，serializers 
设置为a b c,serializers.a.name 为one,serializers.b.name为two,serializers.c.name
为three,那么one->1,two->2,three->3.4foobar5,注意可以不必匹配所有的组)
serializers.x.name 作为event的header

首先看内部类Builder：1）configureSerializers方法用来生成配置项，主要是操作List<NameAndSerializer>，静态内部类NameAndSerializer是一个包含了headerName和RegexExtractorInterceptorSerializer属性的容器，这里每一个serializers.x.name的配置对应一个RegexExtractorInterceptorSerializer对象,RegexExtractorInterceptorSerializer默认是org.apache.flume.interceptor.RegexExtractorInterceptorPassThroughSerializer，即对参数不做任何处理直接返回：

private List<NameAndSerializer> serializerList;
private final RegexExtractorInterceptorSerializer defaultSerializer = new RegexExtractorInterceptorPassThroughSerializer();
....
     private void configureSerializers(Context context) {
      String serializerListStr = context.getString( SERIALIZERS ); //解析serializers的配置
      Preconditions. checkArgument(!StringUtils. isEmpty(serializerListStr),
          "Must supply at least one name and serializer" );
      String[] serializerNames = serializerListStr.split( "\\s+" ); //按空格分隔
      Context serializerContexts =
          new Context(context.getSubProperties( SERIALIZERS + "."));
      serializerList = Lists. newArrayListWithCapacity(serializerNames.length);
      for(String serializerName : serializerNames) { //对每一个serializers里面的设置进行操作
        Context serializerContext = new Context(
            serializerContexts.getSubProperties(serializerName + "." ));
        String type = serializerContext.getString( "type" , "DEFAULT" ); //获取serializers.x.type的设置，默认值是DEFAULT,即org.apache.flume.interceptor.RegexExtractorInterceptorPassThroughSerializer
        String name = serializerContext.getString( "name" ); ////获取serializers.x.name的设置
        Preconditions. checkArgument(!StringUtils. isEmpty(name),
            "Supplied name cannot be empty." );
        if ("DEFAULT" .equals(type)) {
          serializerList .add(new NameAndSerializer(name, defaultSerializer)); //生成NameAndSerializer对象，并加入到List<NameAndSerializer>中，静态内部类NameAndSerializer是一个包含了headerName和RegexExtractorInterceptorSerializer属性的容器，这里每一个serializers.x.name的配置对应一个RegexExtractorInterceptorSerializer对象
        } else {
          serializerList .add(new NameAndSerializer(name, getCustomSerializer(
              type, serializerContext))); //getCustomSerializer用于根据type的设置返回RegexExtractorInterceptorSerializer对象
        }
      }
    }

这里org.apache.flume.interceptor.RegexExtractorInterceptorSerializer 接口类，定义了一个抽象方法serialize,实现类包括:

org.apache.flume.interceptor.RegexExtractorInterceptorPassThroughSerializer 
//直接返回，不做另外的操作(默认的类)
org.apache.flume.interceptor.RegexExtractorInterceptorMillisSerializer 
//使用指定的formatting pattern把传入的值转换为milliseconds

  2）build方法用于返回一个RegexExtractorInterceptor对象

return new RegexExtractorInterceptor( regex , serializerList );

RegexExtractorInterceptor的主要方法intercept：

 static final String REGEX = "regex" ;
  static final String SERIALIZERS = "serializers" ;
...
  public Event intercept(Event event) {
    Matcher matcher = regex.matcher(
        new String(event.getBody(), Charsets.UTF_8)); //对Event的body进行matcher操作
    Map<String, String> headers = event.getHeaders(); // 获取Event的header键值对
    if (matcher.find()) { //检测字符串中的子字符串是否可以匹配到正则
      for ( int group = 0, count = matcher.groupCount(); group < count; group++) {
        int groupIndex = group + 1; // 匹配的index从1开始
        if (groupIndex > serializers .size()) { //判断index是否大于serializers列表(configure产生的List<NameAndSerializer>)的长度
....
          break;
        }
        NameAndSerializer serializer = serializers.get(group); //从serializers中获取对应的NameAndSerializer 对象
....
        headers.put(serializer. headerName,
            serializer. serializer.serialize(matcher.group(groupIndex))); // 向Event中插入headerName和对应的value,这里headerName即为serializers.x.name的设置，value会通过RegexExtractorInterceptorSerializer进行处理
      }
    }
    return event;
  }