WordCount程序代码解

 package com.bigdata.hadoop.wordcount;

 import java.io.IOException;

 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.io.LongWritable;
 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 WordCount {
     /**
      * 设置Map方法
      * @author hxiuz
      *
      */
     private static class WCMapper extends Mapper<LongWritable, Text, Text, IntWritable>{

         private Text mapOutkey = new Text();    //设置输出key的格式
         private final static IntWritable mapOutvalue = new IntWritable(1);    //设置输出value的格式并赋值1
         @Override
         protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, IntWritable>.Context context)
                 throws IOException, InterruptedException {    //key即行偏移量
             String input = value.toString();    //读入value数据
             String[] inArr = input.split(" ");    //按空格分割
             for(String str:inArr) {
                 mapOutkey.set(str);    //给key赋值
                 context.write(mapOutkey, mapOutvalue);    //写入
             }
         }
     }

     /**
      * 设置Reduce方法
      * @author hxiuz
      *
      */
     private static class WCReducer extends Reducer<Text, IntWritable, Text, IntWritable>{
         private IntWritable redOutvalue = new IntWritable();

         @Override
         protected void reduce(Text key, Iterable<IntWritable> values,
                 Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException {
             int sum = 0;    //计数变量
             for(IntWritable value:values) {
                 sum += value.get();    //遍历集合values并将计数累加
             }

             redOutvalue.set(sum);    //给输出value赋值为sum
             context.write(key, redOutvalue);    //写入
         }
     }

     /**
      * 主方法入口
      * @param args
      */
     public static void main(String[] args) {
         // TODO Auto-generated method stub
         if(args.length!=2) {
             System.out.println("Usage:wordcount <in> <out>");
             return ;
         }
         Configuration conf = new Configuration();    //读取配置文件
         try {
             //新建一个job任务实例  并通过类设置jar
             Job job = Job.getInstance(conf, WordCount.class.getSimpleName());
             job.setJarByClass(WordCount.class);

             //设置输入路径
             Path inputPath = new Path(args[0]);
             FileInputFormat.addInputPath(job, inputPath);

             //设置map类
             job.setMapperClass(WCMapper.class);
             //设置map输出的格式
             job.setMapOutputKeyClass(Text.class);
             job.setMapOutputValueClass(IntWritable.class);

             //设置reduce类
             job.setReducerClass(WCReducer.class);
             //设置reduce输出的格式
             job.setOutputKeyClass(Text.class);
             job.setOutputValueClass(IntWritable.class);

             //设置输出路径
             Path outputPath = new Path(args[1]);
             FileOutputFormat.setOutputPath(job, outputPath);

             //提交任务
             boolean jobStatus = job.waitForCompletion(true);    

             //判断程序是否正常退出
             System.exit(jobStatus ? 0 : 1);

         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }

     }

 }