1)需求
在给定的文本文件中统计输出每一个单词出现的总次数。
(1)输入数据
2)期望输出数据
banzhang 1
cls 2
hadoop 1
jiao 1
ss 2
xue 1
2)需求分析
按照MapReduce编程规范,分别编写Mapper,Reducer,Driver。
3)环境准备
(1)创建maven工程,MapReduceDemo
(2)在pom.xml文件中添加如下依赖
<dependencies>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>3.1.3</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.30</version>
</dependency>
</dependencies>
(2)在项目的src/main/resources目录下,新建一个文件,命名为“log4j.properties”,在
(3)创建包名:com.xiaoming.mapreduce.wordcount
4)编写程序
(1)编写Mapper类
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;
public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
Text k = new Text();
IntWritable v = new IntWritable(1);
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
// 1 获取一行
String line = value.toString();
// 2 切割
String[] words = line.split(" ");
// 3 输出
for (String word : words) {
k.set(word);
context.write(k, v);
}
}
}
(2)编写Reducer类
import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable>{
int sum;
IntWritable v = new IntWritable();
@Override
protected void reduce(Text key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException {
// 1 累加求和
sum = 0;
for (IntWritable count : values) {
sum += count.get();
}
// 2 输出
v.set(sum);
context.write(key,v);
}
}
(3)编写Driver驱动类
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 WordCountDriver {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
// 1 获取配置信息以及获取job对象
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
// 2 关联本Driver程序的jar
job.setJarByClass(WordCountDriver.class);
// 3 关联Mapper和Reducer的jar
job.setMapperClass(WordCountMapper.class);
job.setReducerClass(WordCountReducer.class);
// 4 设置Mapper输出的kv类型
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);
// 5 设置最终输出kv类型
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
// 6 设置输入和输出路径
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
// 7 提交job
boolean result = job.waitForCompletion(true);
System.exit(result ? 0 : 1);
}
}
5)本地测试
(1)需要首先配置好HADOOP_HOME变量以及Windows运行依赖
(2)在IDEA/Eclipse上运行程序