Hadoop MapReduce程序开发（二）
根据例WordCount写的一个单词计数器Map类
package com.wordcount.map;
import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
public class Map extends Mapper<Object, Text, Text, IntWritable> {
private static Text word = new Text();
private final static IntWritable one = new IntWritable(1);
@Override
protected void map(Object key, Text value, Context context)
throws IOException, InterruptedException {
//value是每一行数据
StringTokenizer token = new StringTokenizer(value.toString());
while(token.hasMoreTokens()) {
word.set(token.nextToken().toLowerCase());
context.write(word, one);
}
}
}
reduce类
package com.wordcount.reduce;
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
public class Reduce extends Reducer<Text, IntWritable, Text, IntWritable> {
private static IntWritable result = new IntWritable();
@Override
protected void reduce(Text key, Iterable<IntWritable> values, Context context)
throws IOException, InterruptedException {
int total = 0;
for (IntWritable value : values) {
total += value.get();
}
result.set(total);
context.write(key, result);
}
}
配置好eclipse后运行下面类
package com.wordcount.main;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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;
import org.apache.hadoop.util.GenericOptionsParser;
import com.wordcount.map.Map;
import com.wordcount.reduce.Reduce;
public class WordCount {
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] params = new GenericOptionsParser(conf, args).
getRemainingArgs();
if(params.length != 2) {
System.err.println("params error!");
System.exit(2);
}
Job job = new Job(conf, "WordCount");
job.setJarByClass(WordCount.class);
job.setMapperClass(Map.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);
job.setCombinerClass(Reduce.class);
job.setReducerClass(Reduce.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(params));
FileOutputFormat.setOutputPath(job, new Path(params));
System.exit((job.waitForCompletion(true) ? 0 : 1));
}
}
文件words
hello hadoop hello hello world
world cup
just do it
it a test
just try
My World
上传 hadoop fs -put .words /data/input
Run Configuration：
Arguments:
hdfs://master:9000/data/input/words hdfs://master:9000/data/output
结果
a 1
cup 1
do 1
hadoop 1
hello 3
it 2
just 2
my 1
test 1
try 1
world 3
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