【Twitter Storm系列】 Storm简单实例讲解

实例来自书籍《Oreilly.Getting.Started.with.Storm.Aug.2012》

先讲下我们这次所需涉及到的概念：Topology、Spout、Blot

Topology：Storm的运行单位，相当于Hadoop中的job，一个topology是spouts和bolts组成的图， 通过stream groupings将图中的spouts和bolts连接起来

Spout：消息源，topology里面的消息生产者，一般来说消息源会从一个外部源读取数据并且向topology里面发出消息：tuple。

Blot：所有的消息处理逻辑被封装在bolts里面。Bolts可以做很多事情：过滤，聚合，查询数据库等等。

一下是实例的流程图

words.txt--将要执行wordcount操作的文件

storm
test
are
great
is
an
storm
simple
application
but
very
powerfull
really
StOrm
is
great

1、Topology的创建

 	//Topology definition
		TopologyBuilder builder = new TopologyBuilder();
		builder.setSpout("word-reader",new WordReader());
		builder.setBolt("word-normalizer", new WordNormalizer())
			.shuffleGrouping("word-reader");
		builder.setBolt("word-counter", new WordCounter(),1)
			.fieldsGrouping("word-normalizer", new Fields("word"));
		
        //Configuration
		Config conf = new Config();
		conf.put("wordsFile", args[0]);
		conf.setDebug(false);
        //Topology run
		conf.put(Config.TOPOLOGY_MAX_SPOUT_PENDING, 1);
		LocalCluster cluster = new LocalCluster();
		cluster.submitTopology("Getting-Started-Toplogie", conf, builder.createTopology());
		Thread.sleep(1000);
		cluster.shutdown();

从上面代码我们可以看到，Topology是通过TopologyBuilder的createTopology来创建。通过TopologyBuilder对象设置Spout以及Blot。

Config对象用于设置集群计算所需的参数，这里的参数是要执行wordcount操作的文件路径。

例子是以本地集群方式运行。

Topology提交通过cluster对象的submitTopology方法来提交。参数包括任务名、配置、以及Topology对象。

注：我们可以看下这里的TopologyBuilder对象的创建。

TopologyBuilder builder = new TopologyBuilder();
builder.setSpout("word-reader",new WordReader());
builder.setBolt("word-normalizer", new WordNormalizer())
	.shuffleGrouping("word-reader");
builder.setBolt("word-counter", new WordCounter(),1)
	.fieldsGrouping("word-normalizer", new Fields("word"));

可以看出，这里有一个流程的执行关系。也可以说是一定订阅关系。第一个blot设置了shuffleGrouping的名称为Spout的名称，而第二个blot则指定了第一个blot的名称。就如我们上面的流程图执行流程一致。

2、Spout（WordReader）

package spouts;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Map;
import backtype.storm.spout.SpoutOutputCollector;
import backtype.storm.task.TopologyContext;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseRichSpout;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Values;

public class WordReader extends BaseRichSpout {

	private SpoutOutputCollector collector;
	private FileReader fileReader;
	private boolean completed = false;
	public void ack(Object msgId) {
		System.out.println("OK:"+msgId);
	}
	public void close() {}
	public void fail(Object msgId) {
		System.out.println("FAIL:"+msgId);
	}

	/**
	 * The only thing that the methods will do It is emit each 
	 * file line
	 */
	public void nextTuple() {
		/**
		 * The nextuple it is called forever, so if we have been readed the file
		 * we will wait and then return
		 */
		if(completed){
			try {
				Thread.sleep(1000);
			} catch (InterruptedException e) {
				//Do nothing
			}
			return;
		}
		String str;
		//Open the reader
		BufferedReader reader = new BufferedReader(fileReader);
		try{
			//Read all lines
			while((str = reader.readLine()) != null){
				/**
				 * By each line emmit a new value with the line as a their
				 */
				this.collector.emit(new Values(str),str);
			}
		}catch(Exception e){
			throw new RuntimeException("Error reading tuple",e);
		}finally{
			completed = true;
		}
	}

	/**
	 * We will create the file and get the collector object
	 */
	public void open(Map conf, TopologyContext context,
			SpoutOutputCollector collector) {
		try {
			this.fileReader = new FileReader(conf.get("wordsFile").toString());
		} catch (FileNotFoundException e) {
			throw new RuntimeException("Error reading file ["+conf.get("wordFile")+"]");
		}
		this.collector = collector;
	}

	/**
	 * Declare the output field "line"
	 */
	public void declareOutputFields(OutputFieldsDeclarer declarer) {
		declarer.declare(new Fields("line"));
	}
}

* declareOutputFields方法用于定义输出字段名

* 首先集群提交Topology之后，会先调用open方法，open内部使用config对象获取文件并获取fileReader对象。

* nextTuple()方法通过BufferReader读取到fileReader数据之后，读取每一行数据，然后通过emit方法发送数据到订阅了数据的blot上。
3、第一个Blot（拆分出所有的wordcount传入下一个blot）

package bolts;

import backtype.storm.topology.BasicOutputCollector;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseBasicBolt;
import backtype.storm.tuple.Fields;
import backtype.storm.tuple.Tuple;
import backtype.storm.tuple.Values;

public class WordNormalizer extends BaseBasicBolt {

	public void cleanup() {}

	/**
	 * The bolt will receive the line from the
	 * words file and process it to Normalize this line
	 * 
	 * The normalize will be put the words in lower case
	 * and split the line to get all words in this 
	 */
	public void execute(Tuple input, BasicOutputCollector collector) {
        String sentence = input.getString(0);
        String[] words = sentence.split(" ");
        for(String word : words){
            word = word.trim();
            if(!word.isEmpty()){
                word = word.toLowerCase();
                collector.emit(new Values(word));
            }
        }
	}
	

	/**
	 * The bolt will only emit the field "word" 
	 */
	public void declareOutputFields(OutputFieldsDeclarer declarer) {
		declarer.declare(new Fields("word"));
	}
}

这个blot基本上没做什么事情，只是在execute方法中将words切分然后emit到下一个blot

4、第二个blot（执行单词统计）

package bolts;

import java.util.HashMap;
import java.util.Map;

import backtype.storm.task.TopologyContext;
import backtype.storm.topology.BasicOutputCollector;
import backtype.storm.topology.OutputFieldsDeclarer;
import backtype.storm.topology.base.BaseBasicBolt;
import backtype.storm.tuple.Tuple;

public class WordCounter extends BaseBasicBolt {

	Integer id;
	String name;
	Map<String, Integer> counters;

	/**
	 * At the end of the spout (when the cluster is shutdown
	 * We will show the word counters
	 */
	@Override
	public void cleanup() {
		System.out.println("-- Word Counter ["+name+"-"+id+"] --");
		for(Map.Entry<String, Integer> entry : counters.entrySet()){
			System.out.println(entry.getKey()+": "+entry.getValue());
		}
	}

	/**
	 * On create 
	 */
	@Override
	public void prepare(Map stormConf, TopologyContext context) {
		this.counters = new HashMap<String, Integer>();
		this.name = context.getThisComponentId();
		this.id = context.getThisTaskId();
	}

	@Override
	public void declareOutputFields(OutputFieldsDeclarer declarer) {}


	@Override
	public void execute(Tuple input, BasicOutputCollector collector) {
		String str = input.getString(0);
		/**
		 * If the word dosn't exist in the map we will create
		 * this, if not We will add 1 
		 */
		if(!counters.containsKey(str)){
			counters.put(str, 1);
		}else{
			Integer c = counters.get(str) + 1;
			counters.put(str, c);
		}
	}
}

这里定义了一个HashMap counters用于存储单词的统计结果。在execute方法中执行单词统计。

转载请注明来源地址：http://blog.csdn.net/weijonathan/article/details/17399077