Hadoop入门经典:WordCount
以下程序在hadoop1.2.1上测试成功。
本例先将源代码呈现，然后详细说明执行步骤，最后对源代码及执行过程进行分析。
一、源代码
package org.jediael.hadoopdemo.wordcount;
import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
public class WordCount {
public static class WordCountMap extends
Mapper {
private final IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String line = value.toString();
StringTokenizer token = new StringTokenizer(line);
while (token.hasMoreTokens()) {
word.set(token.nextToken());
context.write(word, one);
}
}
}
public static class WordCountReduce extends
Reducer {
public void reduce(Text key, Iterable values,
Context context) throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum += val.get();
}
context.write(key, new IntWritable(sum));
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = new Job(conf);
job.setJarByClass(WordCount.class);
job.setJobName("wordcount");
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
job.setMapperClass(WordCountMap.class);
job.setReducerClass(WordCountReduce.class);
job.setInputFormatClass(TextInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.waitForCompletion(true);
}
}
二、执行程序
1、从eclipse从导出至wordcount.jar，并上传至hadoop服务器，本例中，将程序上传至/home/jediael/project。
2、安装hadoop伪分布模式，可参考Hadoop1.2.1伪分布模式安装指南，本实例将运行在hadoop的伪公布环境中。
3、在HDFS中创建目录wcinput，用作输入目录，并将需要分析的文件复制到目录下。
[root@jediael conf]# hadoop fs -mkdir wcinput
[root@jediael conf]# hadoop fs -copyFromLocal * wcinput
[root@jediael conf]# hadoop fs -ls wcinput
Found 26 items
-rw-r--r-- 1 root supergroup 1524 2014-08-20 12:29 /user/root/wcinput/automaton-urlfilter.txt
-rw-r--r-- 1 root supergroup 1311 2014-08-20 12:29 /user/root/wcinput/configuration.xsl
-rw-r--r-- 1 root supergroup 131090 2014-08-20 12:29 /user/root/wcinput/domain-suffixes.xml
-rw-r--r-- 1 root supergroup 4649 2014-08-20 12:29 /user/root/wcinput/domain-suffixes.xsd
-rw-r--r-- 1 root supergroup 824 2014-08-20 12:29 /user/root/wcinput/domain-urlfilter.txt
-rw-r--r-- 1 root supergroup 3368 2014-08-20 12:29 /user/root/wcinput/gora-accumulo-mapping.xml
-rw-r--r-- 1 root supergroup 3279 2014-08-20 12:29 /user/root/wcinput/gora-cassandra-mapping.xml
-rw-r--r-- 1 root supergroup 3447 2014-08-20 12:29 /user/root/wcinput/gora-hbase-mapping.xml
-rw-r--r-- 1 root supergroup 2677 2014-08-20 12:29 /user/root/wcinput/gora-sql-mapping.xml
-rw-r--r-- 1 root supergroup 2993 2014-08-20 12:29 /user/root/wcinput/gora.properties
-rw-r--r-- 1 root supergroup 983 2014-08-20 12:29 /user/root/wcinput/hbase-site.xml
-rw-r--r-- 1 root supergroup 3096 2014-08-20 12:29 /user/root/wcinput/httpclient-auth.xml
-rw-r--r-- 1 root supergroup 3948 2014-08-20 12:29 /user/root/wcinput/log4j.properties
-rw-r--r-- 1 root supergroup 511 2014-08-20 12:29 /user/root/wcinput/nutch-conf.xsl
-rw-r--r-- 1 root supergroup 42610 2014-08-20 12:29 /user/root/wcinput/nutch-default.xml
-rw-r--r-- 1 root supergroup 753 2014-08-20 12:29 /user/root/wcinput/nutch-site.xml
-rw-r--r-- 1 root supergroup 347 2014-08-20 12:29 /user/root/wcinput/parse-plugins.dtd
-rw-r--r-- 1 root supergroup 3016 2014-08-20 12:29 /user/root/wcinput/parse-plugins.xml
-rw-r--r-- 1 root supergroup 857 2014-08-20 12:29 /user/root/wcinput/prefix-urlfilter.txt
-rw-r--r-- 1 root supergroup 2484 2014-08-20 12:29 /user/root/wcinput/regex-normalize.xml
-rw-r--r-- 1 root supergroup 1736 2014-08-20 12:29 /user/root/wcinput/regex-urlfilter.txt
-rw-r--r-- 1 root supergroup 18969 2014-08-20 12:29 /user/root/wcinput/schema-solr4.xml
-rw-r--r-- 1 root supergroup 6020 2014-08-20 12:29 /user/root/wcinput/schema.xml
-rw-r--r-- 1 root supergroup 1766 2014-08-20 12:29 /user/root/wcinput/solrindex-mapping.xml
-rw-r--r-- 1 root supergroup 1044 2014-08-20 12:29 /user/root/wcinput/subcollections.xml
-rw-r--r-- 1 root supergroup 1411 2014-08-20 12:29 /user/root/wcinput/suffix-urlfilter.txt[root@jediael project]# hadoop org.jediael.hadoopdemo.wordcount.WordCount wcinput wcoutput3
14/08/20 12:50:25 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
14/08/20 12:50:26 INFO input.FileInputFormat: Total input paths to process : 26
14/08/20 12:50:26 INFO util.NativeCodeLoader: Loaded the native-hadoop library
14/08/20 12:50:26 WARN snappy.LoadSnappy: Snappy native library not loaded
14/08/20 12:50:26 INFO mapred.JobClient: Running job: job_201408191134_0005
14/08/20 12:50:27 INFO mapred.JobClient: map 0% reduce 0%
14/08/20 12:50:38 INFO mapred.JobClient: map 3% reduce 0%
14/08/20 12:50:39 INFO mapred.JobClient: map 7% reduce 0%
14/08/20 12:50:50 INFO mapred.JobClient: map 15% reduce 0%
14/08/20 12:50:57 INFO mapred.JobClient: map 19% reduce 0%
14/08/20 12:50:58 INFO mapred.JobClient: map 23% reduce 0%
14/08/20 12:51:00 INFO mapred.JobClient: map 23% reduce 5%
14/08/20 12:51:04 INFO mapred.JobClient: map 30% reduce 5%
14/08/20 12:51:06 INFO mapred.JobClient: map 30% reduce 10%
14/08/20 12:51:11 INFO mapred.JobClient: map 38% reduce 10%
14/08/20 12:51:16 INFO mapred.JobClient: map 38% reduce 11%
14/08/20 12:51:18 INFO mapred.JobClient: map 46% reduce 11%
14/08/20 12:51:19 INFO mapred.JobClient: map 46% reduce 12%
14/08/20 12:51:22 INFO mapred.JobClient: map 46% reduce 15%
14/08/20 12:51:25 INFO mapred.JobClient: map 53% reduce 15%
14/08/20 12:51:31 INFO mapred.JobClient: map 53% reduce 17%
14/08/20 12:51:32 INFO mapred.JobClient: map 61% reduce 17%
14/08/20 12:51:39 INFO mapred.JobClient: map 69% reduce 17%
14/08/20 12:51:40 INFO mapred.JobClient: map 69% reduce 20%
14/08/20 12:51:45 INFO mapred.JobClient: map 73% reduce 20%
14/08/20 12:51:46 INFO mapred.JobClient: map 76% reduce 23%
14/08/20 12:51:52 INFO mapred.JobClient: map 80% reduce 23%
14/08/20 12:51:53 INFO mapred.JobClient: map 84% reduce 23%
14/08/20 12:51:55 INFO mapred.JobClient: map 84% reduce 25%
14/08/20 12:51:59 INFO mapred.JobClient: map 88% reduce 25%
14/08/20 12:52:00 INFO mapred.JobClient: map 92% reduce 25%
14/08/20 12:52:02 INFO mapred.JobClient: map 92% reduce 29%
14/08/20 12:52:06 INFO mapred.JobClient: map 96% reduce 29%
14/08/20 12:52:07 INFO mapred.JobClient: map 100% reduce 29%
14/08/20 12:52:11 INFO mapred.JobClient: map 100% reduce 30%
14/08/20 12:52:15 INFO mapred.JobClient: map 100% reduce 100%
14/08/20 12:52:17 INFO mapred.JobClient: Job complete: job_201408191134_0005
14/08/20 12:52:18 INFO mapred.JobClient: Counters: 29
14/08/20 12:52:18 INFO mapred.JobClient: Job Counters
14/08/20 12:52:18 INFO mapred.JobClient: Launched reduce tasks=1
14/08/20 12:52:18 INFO mapred.JobClient: SLOTS_MILLIS_MAPS=192038
14/08/20 12:52:18 INFO mapred.JobClient: Total time spent by all reduces waiting after reserving slots (ms)=0
14/08/20 12:52:18 INFO mapred.JobClient: Total time spent by all maps waiting after reserving slots (ms)=0
14/08/20 12:52:18 INFO mapred.JobClient: Launched map tasks=26
14/08/20 12:52:18 INFO mapred.JobClient: Data-local map tasks=26
14/08/20 12:52:18 INFO mapred.JobClient: SLOTS_MILLIS_REDUCES=95814
14/08/20 12:52:18 INFO mapred.JobClient: File Output Format Counters
14/08/20 12:52:18 INFO mapred.JobClient: Bytes Written=123950
14/08/20 12:52:18 INFO mapred.JobClient: FileSystemCounters
14/08/20 12:52:18 INFO mapred.JobClient: FILE_BYTES_READ=352500
14/08/20 12:52:18 INFO mapred.JobClient: HDFS_BYTES_READ=247920
14/08/20 12:52:18 INFO mapred.JobClient: FILE_BYTES_WRITTEN=2177502
14/08/20 12:52:18 INFO mapred.JobClient: HDFS_BYTES_WRITTEN=123950
14/08/20 12:52:18 INFO mapred.JobClient: File Input Format Counters
14/08/20 12:52:18 INFO mapred.JobClient: Bytes Read=244713
14/08/20 12:52:18 INFO mapred.JobClient: Map-Reduce Framework
14/08/20 12:52:18 INFO mapred.JobClient: Map output materialized bytes=352650
14/08/20 12:52:18 INFO mapred.JobClient: Map input records=7403
14/08/20 12:52:18 INFO mapred.JobClient: Reduce shuffle bytes=352650
14/08/20 12:52:18 INFO mapred.JobClient: Spilled Records=45210
14/08/20 12:52:18 INFO mapred.JobClient: Map output bytes=307281
14/08/20 12:52:18 INFO mapred.JobClient: Total committed heap usage (bytes)=3398606848
14/08/20 12:52:18 INFO mapred.JobClient: CPU time spent (ms)=14400
14/08/20 12:52:18 INFO mapred.JobClient: Combine input records=0
14/08/20 12:52:18 INFO mapred.JobClient: SPLIT_RAW_BYTES=3207
14/08/20 12:52:18 INFO mapred.JobClient: Reduce input records=22605
14/08/20 12:52:18 INFO mapred.JobClient: Reduce input groups=6749
14/08/20 12:52:18 INFO mapred.JobClient: Combine output records=0
14/08/20 12:52:18 INFO mapred.JobClient: Physical memory (bytes) snapshot=4799041536
14/08/20 12:52:18 INFO mapred.JobClient: Reduce output records=6749
14/08/20 12:52:18 INFO mapred.JobClient: Virtual memory (bytes) snapshot=19545337856
14/08/20 12:52:18 INFO mapred.JobClient: Map output records=22605root@jediael project]# hadoop fs -ls wcoutput3
Found 3 items
-rw-r--r-- 1 root supergroup 0 2014-08-20 12:52 /user/root/wcoutput3/_SUCCESS
drwxr-xr-x - root supergroup 0 2014-08-20 12:50 /user/root/wcoutput3/_logs
-rw-r--r-- 1 root supergroup 123950 2014-08-20 12:52 /user/root/wcoutput3/part-r-00000
[root@jediael project]# hadoop fs -cat wcoutput3/part-r-00000
!! 2
!ci.*.*.us 1
!co.*.*.us 1
!town.*.*.us 1
"AS 22
"Accept" 1
"Accept-Language" 1
"License"); 22
"NOW" 1
"WiFi" 1
"Z" 1
"all" 1
"content" 1
"delete 1
"delimiter" 1三、程序分析
1、WordCountMap类继承了org.apache.hadoop.mapreduce.Mapper，4个泛型类型分别是map函数输入key的类型，输入value的类型，输出key的类型，输出value的类型。
2、WordCountReduce类继承了org.apache.hadoop.mapreduce.Reducer，4个泛型类型含义与map类相同。
3、map的输出类型与reduce的输入类型相同，而一般情况下，map的输出类型与reduce的输出类型相同，因此，reduce的输入类型与输出类型相同。
4、hadoop根据以下代码确定输入内容的格式：
job.setInputFormatClass(TextInputFormat.class);
TextInputFormat是hadoop默认的输入方法，它继承自FileInputFormat。在TextInputFormat中，它将数据集切割成小数据集InputSplit，每一个InputSplit由一个mapper处理。此外，InputFormat还提供了一个RecordReader的实现，将一个InputSplit解析成的形式，并提供给map函数：
key：这个数据相对于数据分片中的字节偏移量，数据类型是LongWritable。
value：每行数据的内容，类型是Text。
因此，在本例中，map函数的key/value类型是LongWritable与Text。
5、Hadoop根据以下代码确定输出内容的格式：
job.setOutputFormatClass(TextOutputFormat.class);
TextOutputFormat是hadoop默认的输出格式，它会将每条记录一行的形式存入文本文件，如
the 30
happy 23
……