Hadoop_数据清洗

示例（去除空行、开头为空格的数据）：

1. 原始数据：D:\data\testdata.txt

zhangsan 500 450 jan
zhangsan 550 450 feb
 lisi 210 150 jan
 lisi 200 150 feb
zhangsan 400 150 march

zhangsan 600 500 april
 lisi 190 150 april
      800 100 jan
BLU 2000 200 feb
lisi 110 10 may

2. DataCleanMapper

package com.blu.dataclean;

import java.io.IOException;

import org.apache.commons.lang3.StringUtils;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class DataCleanMapper extends Mapper<LongWritable, Text, Text, NullWritable>{
	@Override
	protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, NullWritable>.Context context)
			throws IOException, InterruptedException {
		String val = value.toString();
		String[] vals = val.split(" ");
		if(StringUtils.isEmpty(vals[0])) {
			//如果当前行的第一个值是空的，说明不是我们要的数据，直接返回。
			return;
		}
		context.write(value, NullWritable.get());
	}
}

3. DataCleanJob

package com.blu.dataclean;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
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;

public class DataCleanJob {
	public static void main(String[] args) throws Exception {
		Job job = Job.getInstance();
		job.setJarByClass(DataCleanJob.class);
		job.setMapperClass(DataCleanMapper.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(NullWritable.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(NullWritable.class);
		//设置任务数为0
		job.setNumReduceTasks(0);
		FileInputFormat.addInputPath(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		boolean flag = job.waitForCompletion(true);
		System.exit(flag ?0 : 1);
	}
}

4. 运行参数：

D:\data\testdata.txt D:\data\output

5. 运行结果：

zhangsan 500 450 jan
zhangsan 550 450 feb
zhangsan 400 150 march
zhangsan 600 500 april
BLU 2000 200 feb
lisi 110 10 may