Hapdoop的一个Mapreduce示例代码--统计单词个数

package com.mzsx.hadoop;
import java.io.IOException;
import java.util.StringTokenizer;
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.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class MyWordCount {
    public static class MyMapper extends
            Mapper<Object, Text, Text, IntWritable> {
        private final static IntWritable one = new IntWritable(1);// 类似于int类型
        private Text word = new Text(); // 可以理解成String类型
        public void map(Object key, Text value, Context context)
                throws IOException, InterruptedException {
            System.err.println(key + "," + value);
            // 默认情况下即根据空格分隔字符串
            String tmp=value.toString();
            tmp=tmp.replace('\'', ' ');
            tmp=tmp.replace('.', ' ');
            tmp=tmp.replace(',', ' ');
            tmp=tmp.replace(':', ' ');
            tmp=tmp.replace('!', ' ');
            tmp=tmp.replace(';', ' ');
            tmp=tmp.replace('?', ' ');
            tmp=tmp.replace('`', ' ');
            tmp=tmp.replace('"', ' ');
            tmp=tmp.replace('&', ' ');
            tmp=tmp.replace('(', ' ');
            tmp=tmp.replace(')', ' ');
            tmp=tmp.replace('-', ' ');
            StringTokenizer itr = new StringTokenizer(tmp);
            while (itr.hasMoreTokens()) {
                word.set(itr.nextToken());
                context.write(word, one);
            }
        };
    }
    // Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT>
    public static class MyReducer extends
            Reducer<Text, IntWritable, Text, IntWritable> {
        private IntWritable result = new IntWritable();
        protected void reduce(Text key, Iterable<IntWritable> values,
                Context context) throws IOException, InterruptedException {
            System.err.println(key + "," + values);
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            result.set(sum);
            ;
            context.write(key, result);// 这是最后结果
        };
    }
    public static void main(String[] args) throws Exception {
        // 声明配置信息
        Configuration conf = new Configuration();
        // 声明Job
        Job job = new Job(conf, "Word Count");
        // 设置工作类
        job.setJarByClass(MyWordCount.class);
        // 设置mapper类
        job.setMapperClass(MyMapper.class);
        // 可选
        job.setCombinerClass(MyReducer.class);
        // 设置合并计算类
        job.setReducerClass(MyReducer.class);
        // 设置key为String类型
        job.setOutputKeyClass(Text.class);
        // 设置value为int类型
        job.setOutputValueClass(IntWritable.class);
        //job.setInputFormatClass(KeyValueTextInputFormat.class);
        // 设置或是接收输入输出
        FileInputFormat.setInputPaths(job, new Path("/user/root/aoman.txt"));
        FileOutputFormat.setOutputPath(job, new Path("/user/root/out"));
        // 执行
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}