MapReduce实验--计数器

一、Mapreduce计数器。

用来记录job执行的进度和状态, 可以理解为日志, 通过在程序某个位置插入计数器来记录数据或者进度的变化情况。

package Mapreduce_Counters;

import java.io.IOException;

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.Counter;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class Counters {
    
    public static class MyCounterMap extends Mapper<LongWritable, Text, Text, Text> {
        public static Counter ct = null;
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String arr_valueString[] = value.toString().split("\t");
            if (arr_valueString.length > 3) {
                ct = context.getCounter("ErrorCounter", "toolong"); // ErrorCounter为组名，toolong为组员名
                ct.increment(1);
            } else if (arr_valueString.length < 3) {
                ct = context.getCounter("ErrorCounter", "tooshort");
                ct.increment(1);
            }
        }
    }

    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
        if (otherArgs.length != 2) {
            System.out.println("Usage: Counters<in><out>");
            System.exit(2);
        }
        
        Job job = new Job(conf, "MyJob");
        job.setJarByClass(Counters.class);
        job.setMapperClass(MyCounterMap.class);
        
        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
        System.exit(job.waitForCompletion(true)?0:1);
    }
}