mapreduce实例–统计文本中的单词数
一:环境描述:
hadoop2.8.1
文件上传至hdfs,程序从hdfs读取计算,计算结果存储到hdfs
二:前期准备
2.1 上传文件word.txt至hdfs
word.txt 文件内容:
Could not obtain block, Could not obtain block, Could not obtain block
Could not obtain block
Could not obtain block
Could not obtain block
> hdfs dfs -put ./word.txt /user/zhangsan/
2.2 依赖包引入项目:
hadoop-2.8.1\share\hadoop\hdfs\hadoop-hdfs-2.8.1.jar
hadoop-2.8.1\share\hadoop\hdfs\lib\所有jar包
hadoop-2.8.1\share\hadoop\common\hadoop-common-2.8.1.jar
hadoop-2.8.1\share\hadoop\common\lib\所有jar包
hadoop-2.8.1\share\hadoop\mapreduce\除hadoop-mapreduce-examples-2.8.1.jar之外的jar包
hadoop-2.8.1\share\hadoop\mapreduce\lib\所有jar包
hadoop-2.8.1\share\hadoop\yarn\所有jar包
hadoop-2.8.1\share\hadoop\yarn\lib\所有jar包
三:编码
2.1 map类编写
package wordcount;
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
/*
* KEYIN:输入kv数据对中key的数据类型
* VALUEIN:输入kv数据对中value的数据类型
* KEYOUT:输出kv数据对中key的数据类型
* VALUEOUT:输出kv数据对中value的数据类型
*/
public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
/*
* map方法是提供给map task进程来调用的,map task进程是每读取一行文本来调用一次我们自定义的map方法
* map task在调用map方法时,传递的参数:
* 一行的起始偏移量LongWritable作为key
* 一行的文本内容Text作为value
*/
@Override
protected void map(LongWritable key, Text value,Context context) throws IOException, InterruptedException {
//拿到一行文本内容,转换成String 类型
String line = value.toString();
//将这行文本切分成单词
String[] words=line.split(" ");
//输出<单词,1>
for(String word:words){
context.write(new Text(word), new IntWritable(1));
}
}
}
2.2 reduce类编写
package wordcount;
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.io.Text;
/*
* KEYIN:对应mapper阶段输出的key类型
* VALUEIN:对应mapper阶段输出的value类型
* KEYOUT:reduce处理完之后输出的结果kv对中key的类型
* VALUEOUT:reduce处理完之后输出的结果kv对中value的类型
*/
public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable>{
@Override
/*
* reduce方法提供给reduce task进程来调用
*
* reduce task会将shuffle阶段分发过来的大量kv数据对进行聚合,聚合的机制是相同key的kv对聚合为一组
* 然后reduce task对每一组聚合kv调用一次我们自定义的reduce方法
* 比如:<hello,1><hello,1><hello,1><tom,1><tom,1><tom,1>
* hello组会调用一次reduce方法进行处理,tom组也会调用一次reduce方法进行处理
* 调用时传递的参数:
* key:一组kv中的key
* values:一组kv中所有value的迭代器
*/
protected void reduce(Text key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException {
//定义一个计数器
int count = 0;
//通过value这个迭代器,遍历这一组kv中所有的value,进行累加
for(IntWritable value:values){
count+=value.get();
}
//输出这个单词的统计结果
context.write(key, new IntWritable(count));
}
}
2.3 job类编写
package wordcount;
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.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class WordCountJobSubmitter {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
Configuration conf = new Configuration();
Job wordCountJob = Job.getInstance(conf);
//重要:指定本job所在的jar包
wordCountJob.setJarByClass(WordCountJobSubmitter.class);
//设置wordCountJob所用的mapper逻辑类为哪个类
wordCountJob.setMapperClass(WordCountMapper.class);
//设置wordCountJob所用的reducer逻辑类为哪个类
wordCountJob.setReducerClass(WordCountReducer.class);
//设置map阶段输出的kv数据类型
wordCountJob.setMapOutputKeyClass(Text.class);
wordCountJob.setMapOutputValueClass(IntWritable.class);
//设置最终输出的kv数据类型
wordCountJob.setOutputKeyClass(Text.class);
wordCountJob.setOutputValueClass(IntWritable.class);
//设置要处理的文本数据所存放的路径
FileInputFormat.setInputPaths(wordCountJob, "hdfs://172.16.29.11:9000/user/zhangsan/word.txt");
FileOutputFormat.setOutputPath(wordCountJob, new Path("hdfs://172.16.29.11:9000/output/"));
//提交job给hadoop集群
wordCountJob.waitForCompletion(true);
}
}
2.4 eclipse 调试运行
略
2.5 打包运行
打包成mapreduce.jar,并运行
> hadoop jar mapreduce.jar
查看yarn: http://172.16.29.11:8088/cluster/apps 执行成功。
注意
output目录不能存在;如果已存在,执行此命令会报错:Output directory hdfs://172.16.29.11:9000/output already exists
查看输出文件的内容:
> hdfs dfs -ls /output/ # 列出文件
> hdfs dfs -cat /output/part-r-00000 # 查看此文件内容
>
Could 6
block 4
block, 2
not 6
obtain 6
参考博文:https://blog.csdn.net/litianxiang_kaola/article/details/71154302