WordCount案例实操
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
1
lin 1
shi 2
wo 2
xiang 1
xinyue 2
2．需求分析
按照MapReduce编程规范，分别编写Mapper，Reducer，Driver，如图所示。
3．环境准备
（1）创建maven工程
（2）在pom.xml文件中添加如下依赖
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>RELEASE</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.8.2</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>2.7.2</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>2.7.2</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>2.7.2</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”，在文件中填入。
log4j.rootLogger=INFO, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n
log4j.appender.logfile=org.apache.log4j.FileAppender
log4j.appender.logfile.File=target/spring.log
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n
4．编写程序
（1）编写Mapper类
package com.hadoop.mapreduce;/*
作者 :XiangLin
创建时间 :17/08/2020 23:39
文件 :WordcountMapper.java
IDE :IntelliJ IDEA
*/
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
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
package com.hadoop.mapreduce;/*
作者 :XiangLin
创建时间 :17/08/2020 23:49
文件 :WordcountReducer.java
IDE :IntelliJ IDEA
*/
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import java.io.IOException;
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
package com.hadoop.mapreduce;/*
作者 :XiangLin
创建时间 :17/08/2020 23:53
文件 :WordcountDriver.java
IDE :IntelliJ IDEA
*/
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 java.io.IOException;
public class WordcountDriver {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
Configuration conf = new Configuration();
//1.获取job对象
Job job = Job.getInstance(conf);
// 2设置jar存储位置
job.setJarByClass(WordcountDriver.class);
// 3关联Map和Reduce类
job.setMapperClass(WordcountMapper.class);
job.setReducerClass(WordcountReducer.class);
// 4设置Mapper阶段输出数据的key和value
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);
// 5设置最终数据输出的key和value类型
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
// 6设置输出路径和输出路径
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
运行，设置输出输出参数
d:/xiaoyue.txt d:/outputt
6．集群上测试
（0）用maven打jar包，需要添加的打包插件依赖
注意：
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin </artifactId>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>com.hadoop.mr.WordcountDriver</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
注意：如果工程上显示红叉。在项目上右键->maven->update project即可。
修改不带依赖的jar包名称为wc.jar，并拷贝该jar包到Hadoop集群。
（2）启动Hadoop集群
（3）执行WordCount程序
[hadoop@hadoop102 hadoop-2.7.2]$ hadoop jar wc.jar com.hadoop.mapreduce.WordcountDriver /user/hadoop/input /user/hadoop/output
[hadoop@hadoop102 hadoop-2.7.2]$ hadoop fs -cat /user/hadoop/output/part-r-00000
gu 1
lu 1
mao 1
san 1
shi 2
wo 2
woshibossxiang 2
xinyue 2
注：博主在运行：博主在运行过程当中发现一个问题，就是运行的时候一直卡死
这里里一直不动，还发现集群始终只显示一个节点
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发现问题，
解决方法：关闭hadoop集群，修改hosts文件，命令：sudo vi /etc/hosts，三台机子都要修改
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