需求

對以下txt文檔進行單詞出現次數統計（txt文檔在/Users/lizhengi/test/input/目錄下）

hadoop take spring
spark hadoop hdfs
mapreduce take Tomcat
tomcat
kafka kafka flume
flume
hive

實現

1、新建Maven工程，pom.xml依賴如下

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.lizhengi</groupId><artifactId>Hadoop-API</artifactId><version>1.0-SNAPSHOT</version><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>3.2.1</version></dependency><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-client</artifactId><version>3.2.1</version></dependency><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-hdfs</artifactId><version>3.2.1</version></dependency></dependencies></project>

2、src/main/resources目錄下，新建一個文件，命名為“log4j.properties”，添加內容如下

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

3、編寫Mapper類-WcMapper

package com.lizhengi.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;/*** @author lizhengi* @create 2020-07-20*/
public class WcMapper extends Mapper<LongWritable, Text, Text, IntWritable> {Text k = new Text();IntWritable v = new IntWritable(1);@Overrideprotected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {// 1 拿到傳入進來的一行內容，把數據類型轉化為StringString line = value.toString();// 2 將這一行內容按照分隔符進行一行內容的切割 切割成一個單詞數組String[] words = line.split(" ");// 3 遍歷數組，每出現一個單詞  就標記一個數字1  <單詞，1>for (String word : words) {//使用mr程序的上下文context 把mapper階段處理的數據發送出去//作為reduce節點的輸入數據k.set(word);context.write(k, v);}}
}

4、編寫Reducer類-WcReducer

package com.lizhengi.wordcount;import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;/*** @author lizhengi* @create 2020-07-20*/
public class WcReducer extends Reducer<Text, IntWritable, Text, IntWritable>{int sum;IntWritable v = new IntWritable();@Overrideprotected void reduce(Text key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException {// 1 定義一個計數器sum = 0;// 2 遍歷一組迭代器，把每一個數量1累加起來就構成了單詞的總次數for (IntWritable count : values) {sum += count.get();}// 3 輸出最終的結果v.set(sum);context.write(key,v);}
}

5、編寫Driver驅動類-WcDriver

package com.lizhengi.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;/*** @author lizhengi* @create 2020-07-20*/
public class WcDriver {public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {// 1 獲取配置信息以及封裝任務Configuration configuration = new Configuration();Job job = Job.getInstance(configuration);// 2 設置jar加載路徑job.setJarByClass(WcDriver.class);// 3 設置map和reduce類job.setMapperClass(WcMapper.class);job.setReducerClass(WcReducer.class);// 4 設置map輸出job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(IntWritable.class);// 5 設置最終輸出kv類型job.setOutputKeyClass(Text.class);job.setOutputValueClass(IntWritable.class);// 6 設置輸入和輸出路徑FileInputFormat.setInputPaths(job, "/Users/lizhengi/test/input");FileOutputFormat.setOutputPath(job, new Path("/Users/lizhengi/test/output"));// 7 提交boolean result = job.waitForCompletion(true);System.exit(result ? 0 : 1);}
}

結果

[root@carlota1]ls /Users/lizhengi/test/output/
#多了兩個文件
_SUCCESS	part-r-00000

[root@carlota1 output]cat part-r-00000
flume	2
hadoop	2
hdfs	1
hive	1
kafka	2
mapreduce	1
spark 	1
spring	1
take	2
tomcat		2