文本文檔words.txt
hello tom
hello lina
hello tom
hello GPY
HI selina
結果樣式:
GPY 1
HI 1
hello 4
lina 1
selina 1
tom 2
Java代碼:
package MR;
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 WC{
//定義Mapper類,四個參數分别是(map讀入的偏移量類型,值類型,map即将輸出的鍵類型值類型)
public static class MyMap extends Mapper<LongWritable, Text, Text, IntWritable>{
@Override
protected void map(LongWritable key, Text value,Context context)
throws IOException, InterruptedException {
String[] fields = value.toString().split(" ");//把讀入的一行資料,按空格切割
for(String s: fields){
context.write(new Text(s), new IntWritable(1));//每一單詞都作為鍵值,并賦予value1,作為詞頻的基本數
}
}
}
//定義reducer類,四個參數分别是(map輸出的鍵類型,值類型,reducer即将輸出的鍵類型值類型)
public static class MyReduce extends Reducer<Text, IntWritable, Text, IntWritable>{
@Override
protected void reduce(Text key, Iterable<IntWritable> values,//此時經過shuffle已經将value變為數組
Context context) throws IOException, InterruptedException {
int count=0;
for(IntWritable i:values){
count+=i.get();//在ruducer裡把每個值相加
}
context.write(key, new IntWritable(count));//
}
}
public static void main(String[] args) {
Configuration conf=new Configuration();
try {
Job job=Job.getInstance(conf);
job.setJarByClass(WC.class);//設定主類
job.setMapperClass(MyMap.class);//加載map類
job.setReducerClass(MyReduce.class);//加載reduce類
job.setOutputKeyClass(Text.class);//輸出的KEY格式
job.setOutputValueClass(IntWritable.class);//輸出的value格式
Path inPath =new Path("/input/words.txt");
FileInputFormat.addInputPath(job, inPath);
Path outpath=new Path("/output/WordCount/result");
if(outpath.getFileSystem(conf).exists(outpath)){
outpath.getFileSystem(conf).delete(outpath, true);
}
FileOutputFormat.setOutputPath(job, outpath);
job.waitForCompletion(true);
} catch (Exception e) {
// TODO Auto-generate
// .d catch block
e.printStackTrace();
}
}
}