WeekDay.java

import java.io.IOException;
import java.util.Locale;
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 WeekDay {

	public static class RegexMapper extends Mapper<Object, Text, Text, IntWritable>{

        private final static long OneK = 1000L;
		private final static IntWritable one = new IntWritable(1);
		private Text word = new Text();

		public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
			String valueStr = value.toString();
			String[] fields = valueStr.split("\\s");
            if (fields.length == 4) {
                String user = fields[0];
                String article = fields[1];
                String edit = fields[2];
                String timestamp = fields[3];	
                long epochSeconds = Long.valueOf(timestamp);
                String weekday = String.format(Locale.ENGLISH, "%tA", epochSeconds * OneK);
                word.set(weekday);
                context.write(word, one);
            } 
		}
	}

	public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable> {
		private IntWritable result = new IntWritable();

		public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
			int sum = 0;
			for (IntWritable val : values) {
				sum += val.get();
			}
			result.set(sum);
			context.write(key, result);
		}
	}

	public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		Job job = Job.getInstance(conf, "day of week count");
		job.setJarByClass(WeekDay.class);
		job.setMapperClass(RegexMapper.class);
		job.setCombinerClass(IntSumReducer.class);
		job.setReducerClass(IntSumReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}