MapReduce经典案例分享

最新推荐文章于 2024-04-09 15:34:01 发布

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最新推荐文章于 2024-04-09 15:34:01 发布

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文章标签：大数据操作系统 java

本文介绍了一个使用Hadoop MapReduce框架实现的学生平均分计算程序。该程序通过Map阶段收集学生姓名及其各科成绩，Reduce阶段则计算每个学生的平均分数。

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资源文件math

张三 99

李四 90

王五 90

赵六 60

资源文件china

张三 79

李四 75

王五 80

赵六 90

资源文件english

张三 89

李四 75

王五 70

赵六 90

分析：

map 阶段将将学生姓名作为key 成绩作为value.这样Reduce阶段得到的数据就是

key:张三 value:{99,79,89}

……

在Reduce中将学生的成绩球平均值。

实现：

package com.bwzy.Hadoop;
import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configured;
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.Reducer.Context;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
import com.bwzy.hadoop.HeBing.Map;
import com.bwzy.hadoop.HeBing.Reduce;
public class AvgSorce extends Configured implements Tool {
public static class Map extends Mapper<LongWritable, Text, Text, IntWritable> {
public void map(LongWritable key, Text value, Context context) throws IOException,InterruptedException {
String line = value.toString();
StringTokenizer tokenizer = new StringTokenizer(line);
while(tokenizer.hasMoreElements()){
String strName = tokenizer.nextToken();
String strSorce = tokenizer.nextToken();
context.write(new Text(strName), new IntWritable(Integer.parseInt(strSorce)));
}
}
}
public static class Reduce extends Reducer<Text, IntWritable, Text, IntWritable> {
public void reduce(Text key, Iterable<IntWritable> values, Context context)
throws IOException, InterruptedException {
int sum = 0;
int num = 0;
for (IntWritable sorce : values) {
sum+=sorce.get();
num++;
}
context.write(key, new IntWritable((int)(sum/num)));
}
}
@Override
public int run(String[] arg0) throws Exception {
Job job = new Job(getConf());
job.setJobName("AvgSorce");
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
job.setMapperClass(Map.class);
// job.setCombinerClass(Reduce.class);
job.setReducerClass(Reduce.class);
job.setInputFormatClass(TextInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);
FileInputFormat.setInputPaths(job, new Path(arg0[0]));
FileOutputFormat.setOutputPath(job, new Path(arg0[1]));
boolean success = job.waitForCompletion(true);
return success ? 0 : 1;
}
public static void main(String[] args) throws Exception {
int ret = ToolRunner.run(new AvgSorce(), args);
System.exit(ret);
}
}