Hadoop示例程序之单词统计MapReduce

在eclipse下新建一个map/reduce Project

1,新建文件MyMap.java

import java.io.IOException;

import java.util.StringTokenizer;



import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Mapper;



public class MyMap extends Mapper<Object, Text, Text, IntWritable> {

private final static IntWritable one = new IntWritable(1);



private Text word;



public void map(Object key, Text value, Context context)

throws IOException, InterruptedException {



String line = value.toString();

StringTokenizer tokenizer = new StringTokenizer(line);

while (tokenizer.hasMoreTokens()) {

word = new Text();

word.set(tokenizer.nextToken());

context.write(word, one);

}

}

}



2，新建文件MyReduce.java:

import java.io.IOException;



import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Reducer;



public class MyReduce 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));

}

}

3，新建一个文件MyDriver.java

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Job;

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 MyDriver {





public static void main(String[] args) throws Exception,InterruptedException {

Configuration conf=new Configuration();



Job job=new Job(conf,"Hello Hadoop World");



job.setJarByClass(MyDriver.class);



job.setMapOutputKeyClass(Text.class);

job.setMapOutputValueClass(IntWritable.class);



job.setOutputKeyClass(Text.class);

job.setOutputValueClass(IntWritable.class);



job.setMapperClass(MyMap.class);

job.setCombinerClass(MyReduce.class);

job.setReducerClass(MyReduce.class);



job.setInputFormatClass(TextInputFormat.class);

job.setOutputFormatClass(TextOutputFormat.class);



FileInputFormat.setInputPaths(job, new Path("./input/555.txt"));



FileOutputFormat.setOutputPath(job, new Path("./input/out.txt"));

job.waitForCompletion(true);

}



}

好了，见证奇迹的时刻到了，先在工程目录下创建一个目录input,并在下面新建文件555.txt,

Hello World 555 hahaha

Hello World

保存，运行java应用程序

在input下多了个文件目录:out.txt，该目录下有个文件part-r-0000文件，

打开后文件的内容是：

555 1

Hello 2

World 2

hahaha 1

算是搞定了。。。

运行中碰到包错：

org.apache.hadoop.fs.ChecksumException: Checksum error:

这个好办 只要将工程文件下的CRC数据校验文件删除就可以了