Hadoop 实践（二） Mapreduce 编程

古城堡

　　Mapreduce 编程，本文以WordCount  为例：实现文件字符统计
　　在eclipse 里面搭建一个java项目，引入hadoop lib目录下的jar，和 hadoop主目录下的jar。
　　新建WordCount 类：
　　package org.scf.wordcount;
　　import java.io.IOException;
　　import java.util.*;
　　import org.apache.hadoop.fs.Path;
　　import org.apache.hadoop.conf.*;
　　import org.apache.hadoop.io.*;
　　import org.apache.hadoop.mapred.*;
　　import org.apache.hadoop.util.*;

　　public>
　　public static>　　private final static IntWritable one = new IntWritable(1);
　　private Text word = new Text();
　　public void map(LongWritable key, Text value, OutputCollector output, Reporter reporter) throws IOException {
　　String line = value.toString();
　　StringTokenizer tokenizer = new StringTokenizer(line);
　　while (tokenizer.hasMoreTokens()) {
　　word.set(tokenizer.nextToken());
　　output.collect(word, one);
　　}
　　}
　　}

　　public static>　　public void reduce(Text key, Iterator values, OutputCollector output, Reporter reporter) throws IOException {
　　int sum = 0;
　　while (values.hasNext()) {
　　sum += values.next().get();
　　}
　　output.collect(key, new IntWritable(sum));
　　}
　　}
　　public static void main(String[] args) throws Exception {
　　JobConf conf = new JobConf(WordCount.class);
　　conf.setJobName("wordcount");
　　conf.setOutputKeyClass(Text.class);
　　conf.setOutputValueClass(IntWritable.class);
　　conf.setMapperClass(Map.class);
　　conf.setCombinerClass(Reduce.class);
　　conf.setReducerClass(Reduce.class);
　　conf.setInputFormat(TextInputFormat.class);
　　conf.setOutputFormat(TextOutputFormat.class);
　　FileInputFormat.setInputPaths(conf, new Path(args[0]));
　　FileOutputFormat.setOutputPath(conf, new Path(args[1]));
　　JobClient.runJob(conf);
　　}
　　}
　　2.编译，运行该类
　　cd /home/Hadoop/
　　mkdir wordcount_classes
　　javac -classpath /usr/hadoop-1.0.4/hadoop-core-1.0.4.jar -d /home/Hadoop/wordcount_classes WordCount.java
　　jar -cvf /home/Hadoop/wordcount.jar -C /home/Hadoop/wordcount_classes/ .
　　hadoop dfs -put /home/Hadoop/test.txt  /user/root/wordcount/input/file2
　　hadoop dfs -put /home/Hadoop/test1.txt  /user/root/wordcount/input/file3
　　hadoop jar /home/Hadoop/wordcount.jar org.scf.wordcount.WordCount /user/root/wordcount/input /user/root/wordcount/output
　　hadoop dfs -ls /user/root/wordcount/output
　　hadoop dfs -cat /user/root/wordcount/output/part-00000