【Hadoop】编写和运行WordCount.java

1，在Hadoop文件夹下，比如在Linux系统下，Hadoop解压缩后的文件夹。

该文件夹下有 bin, conf, ivy, lib, sbin, share, src等文件夹，也有 hadoop-client-1.2.1.jar, hadoop-examples-1.2.1.jar等文件。目前设该文件夹的

路径为 /usr/local/hadoop。

首先编写 /usr/local/hadoop/WordCount.java：

package org.myorg;

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 class WordCount {

public static class Map extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();

public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> 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 class Reduce extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {
public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> 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，开始编译。
WordCount.java中引入了org.apache.hadooop.*等多个包，这些都是在hadoop-core-1.2.1.jar, hadoop-client.1.2.1.jar等jar文件中。

2.1 首先，建立一个新的文件夹 /usr/local/hadoop/wordcount_classes

在/usr/local/hadoop文件夹下直接输入： mkdir wordcount_classes

2.2 编译

注意，多个jar包直接用【冒号】连接。

javac -classpath /usr/local/hadoop/hadoop-core-1.2.1.jar:/usr/local/hadoop/hadoop-client-1.2.1.jar -d wordcount_classes/ WordCount.java

这个步骤之后，会在wordcount_classes下面成功生成： org/myorg/的二级子目录，在myorg目录下会有：

WordCount.class  WordCount$Map.class  WordCount$Reduce.class

等子文件

3，打包成jar包

jar -cvf WordCount.jar -C wordcount_classes ./

打包成目标文件：WordCount.jar

4，在Hadoop的dfs中新建文件夹：

./bin/hadoop dfs -mkdir /user/hadoop/wordcount

./bin/hadoop dfs -mkdir /user/hadoop/wordcount/input

5，生成文件，和把文件放进dfs中

echo "Hello World Bye World" > file0
echo "Hello Hadoop Goodbye Hadoop" > file1
./bin/hadoop dfs -put file* /user/hadoop/wordcount/input

6，运行

./bin/hadoop jar WordCount.jar org.myorg.WordCount /user/hadoop/wordcount/input /user/hadoop/wordcount/output

7，结果

Warning: $HADOOP_HOME is deprecated.

14/06/20 17:29:55 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
14/06/20 17:29:55 INFO util.NativeCodeLoader: Loaded the native-hadoop library
14/06/20 17:29:55 WARN snappy.LoadSnappy: Snappy native library not loaded
14/06/20 17:29:55 INFO mapred.FileInputFormat: Total input paths to process : 2
14/06/20 17:29:58 INFO mapred.JobClient: Running job: job_201406201518_0001
14/06/20 17:29:59 INFO mapred.JobClient:  map 0% reduce 0%
14/06/20 17:32:55 INFO mapred.JobClient:  map 33% reduce 0%
14/06/20 17:33:05 INFO mapred.JobClient:  map 66% reduce 0%
14/06/20 17:33:24 INFO mapred.JobClient:  map 100% reduce 0%
14/06/20 17:33:29 INFO mapred.JobClient:  map 100% reduce 22%
14/06/20 17:33:31 INFO mapred.JobClient:  map 100% reduce 100%
14/06/20 17:33:33 INFO mapred.JobClient: Job complete: job_201406201518_0001
14/06/20 17:33:33 INFO mapred.JobClient: Counters: 30
14/06/20 17:33:33 INFO mapred.JobClient:   Job Counters
14/06/20 17:33:33 INFO mapred.JobClient:     Launched reduce tasks=1
14/06/20 17:33:33 INFO mapred.JobClient:     SLOTS_MILLIS_MAPS=369084
14/06/20 17:33:33 INFO mapred.JobClient:     Total time spent by all reduces waiting after reserving slots (ms)=0
14/06/20 17:33:33 INFO mapred.JobClient:     Total time spent by all maps waiting after reserving slots (ms)=0
14/06/20 17:33:33 INFO mapred.JobClient:     Launched map tasks=3
14/06/20 17:33:33 INFO mapred.JobClient:     Data-local map tasks=3
14/06/20 17:33:33 INFO mapred.JobClient:     SLOTS_MILLIS_REDUCES=29759
14/06/20 17:33:33 INFO mapred.JobClient:   File Input Format Counters
14/06/20 17:33:33 INFO mapred.JobClient:     Bytes Read=53

./bin/hadoop dfs -cat /user/hadoop/wordcount/output/part-00000

RESULT:

Warning: $HADOOP_HOME is deprecated.

Bye	1
Goodbye	1
Hadoop	2
Hello	2
World	2