Hadoop入门经典:WordCount

转：http://blog.csdn.net/jediael_lu/article/details/38705371

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<LongWritable, Text, Text, IntWritable> {  
  
        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<Text, IntWritable, Text, IntWritable> {  
  
        public void reduce(Text key, Iterable<IntWritable> 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);  
    }  
}  

[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 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