KeyValueTextInputFormat使用案例

统计输入文件中每一行的第一个单词相同的行数。
（1）输入数据
banzhang ni hao
xihuan hadoop banzhang
banzhang ni hao
xihuan hadoop banzhang
（2）期望结果数据
banzhang 2
xihuan 2

map类

package KVText;


import java.io.IOException;

//banzhang ni hao

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class KVTextMapper extends Mapper<Text, Text, Text, LongWritable>{
    
    
	
	//设置value
	LongWritable v = new LongWritable(1);
	
	@Override
	protected void map(Text key, Text value, Mapper<Text, Text, Text, LongWritable>.Context context)
			throws IOException, InterruptedException {
    
    
		
			//写出
		context.write(key, v);
	}

}

reducer类

package KVText;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class KVTextReducer extends Reducer<Text, LongWritable, Text, LongWritable>{
    
    
	
	LongWritable v = new LongWritable();
	
	@Override
protected void reduce(Text key, Iterable<LongWritable> values,
		Context context) throws IOException, InterruptedException {
    
    

		//累计求和
		Long sum = 0L;
		for (LongWritable value : values) {
    
    
			sum += value.get();
		}
		
		v.set(sum);
		
		//写出
		context.write(key, v);
}
}

dirver类

package KVText;

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.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.KeyValueTextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class KVTextDriver {
    
    
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
    
    
	args=new String[] {
    
    "e:input2","e:/output8"};
	//设置切割符
	Configuration conf = new Configuration();
	
	//获取job对象
	Job job = Job.getInstance(conf);
	
	//设置jar包路径
	job.setJarByClass(KVTextDriver.class);
	
	//关联mapper和reduce
	job.setMapperClass(KVTextMapper.class);
	job.setReducerClass(KVTextReducer.class);
	
	//设置map输出kv类型
	job.setMapOutputKeyClass(Text.class);
	job.setMapOutputValueClass(LongWritable.class);
	
	//设置最终输出kv类型
	job.setOutputKeyClass(Text.class);
	job.setOutputValueClass(LongWritable.class);
	
	//设置输入输出路径
	FileInputFormat.setInputPaths(job, new Path(args[0]));
	
	//设置输入格式
	job.setInputFormatClass(KeyValueTextInputFormat.class);
	
	//设置输出数据路径
	FileOutputFormat.setOutputPath(job, new Path(args[1]));
	
	//提交job
	boolean result = job.waitForCompletion(true);
	System.exit(result ? 0:1);
}
}