flumeソース分析-channelSelector

flumeには2種類のchannelSelectorが付属しています.1つはM u l t i p l e xingChannelSelector、もう1つはReplicatingChannelSelectorです.
 
ReplicatingChannelSelectorはeventを各channelに送信する

public class ReplicatingChannelSelector extends AbstractChannelSelector {

  private final List<Channel> emptyList = Collections.emptyList();

  @Override
  public List<Channel> getRequiredChannels(Event event) {
    return getAllChannels();
  }

  @Override
  public List<Channel> getOptionalChannels(Event event) {
    return emptyList;
  }

  @Override
  public void configure(Context context) {
    // No configuration necessary
  }
}

M u l t i p l e xingChannelSelectorはheaderの構成に従ってeventを対応するchannelに送信する

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package org.apache.flume.channel;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.flume.Channel;
import org.apache.flume.Context;
import org.apache.flume.Event;
import org.apache.flume.FlumeException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MultiplexingChannelSelector extends AbstractChannelSelector {

  public static final String CONFIG_MULTIPLEX_HEADER_NAME = "header";
  public static final String DEFAULT_MULTIPLEX_HEADER =
      "flume.selector.header";
  public static final String CONFIG_PREFIX_MAPPING = "mapping.";
  public static final String CONFIG_DEFAULT_CHANNEL = "default";
  @SuppressWarnings("unused")
  private static final Logger LOG = LoggerFactory
    .getLogger(MultiplexingChannelSelector.class);

  private static final List<Channel> EMPTY_LIST =
      Collections.emptyList();

  private String headerName;

  private Map<String, List<Channel>> channelMapping;

  private List<Channel> defaultChannels;
  @Override
  public List<Channel> getRequiredChannels(Event event) {
    String headerValue = event.getHeaders().get(headerName);
    if (headerValue == null || headerValue.trim().length() == 0) {
      return defaultChannels;
    }

    List<Channel> channels = channelMapping.get(headerValue);

    //This header value does not point to anything
    //Return default channel(s) here.
    if (channels == null) {
      channels = defaultChannels;
    }

    return channels;
  }

  @Override
  public List<Channel> getOptionalChannels(Event event) {
    return EMPTY_LIST;
  }

  @Override
  public void configure(Context context) {
    this.headerName = context.getString(CONFIG_MULTIPLEX_HEADER_NAME,
        DEFAULT_MULTIPLEX_HEADER);

    Map<String, Channel> channelNameMap = new HashMap<String, Channel>();
    for (Channel ch : getAllChannels()) {
      channelNameMap.put(ch.getName(), ch);
    }

    defaultChannels = getChannelListFromNames(
        context.getString(CONFIG_DEFAULT_CHANNEL), channelNameMap);

    if(defaultChannels.isEmpty()){
      throw new FlumeException("Default channel list empty");
    }

    Map<String, String> mapConfig =
        context.getSubProperties(CONFIG_PREFIX_MAPPING);

    channelMapping = new HashMap<String, List<Channel>>();

    for (String headerValue : mapConfig.keySet()) {
      List<Channel> configuredChannels = getChannelListFromNames(
          mapConfig.get(headerValue),
          channelNameMap);

      //This should not go to default channel(s)
      //because this seems to be a bad way to configure.
      if (configuredChannels.size() == 0) {
        throw new FlumeException("No channel configured for when "
            + "header value is: " + headerValue);
      }

      if (channelMapping.put(headerValue, configuredChannels) != null) {
        throw new FlumeException("Selector channel configured twice");
      }
    }
    //If no mapping is configured, it is ok.
    //All events will go to the default channel(s).

  }

  //Given a list of channel names as space delimited string,
  //returns list of channels.
  private List<Channel> getChannelListFromNames(String channels,
      Map<String, Channel> channelNameMap){
    List<Channel> configuredChannels = new ArrayList<Channel>();
    String[] chNames = channels.split(" ");
    for (String name : chNames) {
      Channel ch = channelNameMap.get(name);
      if (ch != null) {
        configuredChannels.add(ch);
      } else {
        throw new FlumeException("Selector channel not found: "
            + name);
      }
    }
    return configuredChannels;
  }

}