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

补充：软件开发 , Java ,