Map Reduce
WordCount
用IDEA创建一个maven工程wordcountmr(单词计数程序)
在pom.xml中引入Hadoop依赖包
<dependencies>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>2.9.1</version>
</dependency>
</dependencies>
新建WordCountMR.Class
package com.cniao5;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
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.FileOutputCommitter;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import java.io.IOException;
public class WordCountMR{
public static class WordCountMapper extends Mapper<LongWritable, Text, Text, LongWritable> {
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
String line = value.toString();
String[] words = line.split("\t");
for(String word:words) {
context.write(new Text(word), new LongWritable(1));
}
}
}
public static class WordCountReducer extends Reducer<Text, LongWritable, Text, LongWritable>{
@Override
protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {
int count = 0;
for(LongWritable value:values){
count += value.get();
}
context.write(key, new LongWritable(count));
}
}
public static void main( String[] args ) throws IOException, ClassNotFoundException, InterruptedException {
String input = args[0];
String output = args[1];
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJobName("wordcount");
job.setJarByClass(WordCountMR.class);
job.setMapperClass(WordCountMapper.class);
job.setReducerClass(WordCountReducer.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(LongWritable.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(LongWritable.class);
FileInputFormat.setInputPaths(job,new Path(input));
FileOutputFormat.setOutputPath(job, new Path(output));
System.exit(job.waitForCompletion(true)?0:1);
}
}
打包jar包,View-Tool Windows-Maven Projects- 双击package完成打包,在target文件夹下wordcountmr-1.0-SNAPSHOT.jar
将此jar包拷贝到Linux机器上执行
在hdfs上新建一个input文件夹,下面放一个要计数的文件(自己写若干的单词,空格隔开)
hadoop jar ./wordcountmr-1.0-SNAPSHOT.jar mr.WordCountMR /input /output
等待程序结束,输出在output下