flume源码分析-ChannelSelector

张颢镡

　　flume自带两种channelSelector。一种是MultiplexingChannelSelector，另一种是ReplicatingChannelSelector。
　　ReplicatingChannelSelector是将event发送到每个channel

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
}
}
　　MultiplexingChannelSelector按照header的配置将event发送到相应的channel

/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements.  See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership.  The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License.  You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied.  See the License for the
* specific language governing permissions and limitations
* under the License.
*/
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;
}
}