Hadoop快速入门——第三章、MapReduce案例(字符统计)（1）

<dependencies>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.7.3</version>
        </dependency>
    </dependencies>

package com.item.test;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
public class MapAction extends Mapper<LongWritable, Text, Text, LongWritable> {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        char[] split = value.toString().toCharArray();
        for (char s : split) {
            context.write(new Text(s+""), new LongWritable(1));
        }
    }
}

package com.item.test;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import java.io.IOException;
public class ReduceAction extends Reducer<Text, LongWritable, Text, LongWritable> {
    @Override
    protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {
        long count = 0;
        for (LongWritable value : values) {
            count += value.get();
        }
        context.write(key, new LongWritable(count));
    }
}

package com.item.test;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
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.output.FileOutputFormat;
import java.io.IOException;
public class Action {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(Action.class);
        job.setMapperClass(MapAction.class);
        job.setReducerClass(ReduceAction.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongWritable.class);
        //本地测试
        FileInputFormat.setInputPaths(job,new Path("D:\\info.txt"));
        FileOutputFormat.setOutputPath(job,new Path("D:\\infos"));
        boolean b = job.waitForCompletion(true);
        System.exit(b?0:1);
    }
}