MapReduce编程初体验

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

第一步： 准备一个aaa.txt文本文档
第二步： 在文本文档中随便写入一些测试数据，这里我写入的是

hello,world,hadoop
hello,hive,sqoop,flume
kitty,tom,jerry,world
hadoop

第三步： 打开编码器（我用的是idea）

新建一个项目…

创建maven项目 不用选择框架

修改pom文件

<?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>cn.itcast</groupId><artifactId>mapreduce</artifactId><version>1.0-SNAPSHOT</version><repositories><repository><id>cloudera</id><url>https://repository.cloudera.com/artifactory/cloudera-repos/</url></repository></repositories><dependencies><dependency><groupId>org.apache.Hadoop</groupId><artifactId>Hadoop-client</artifactId><version>2.6.0-mr1-cdh5.14.0</version></dependency><dependency><groupId>org.apache.Hadoop</groupId><artifactId>Hadoop-common</artifactId><version>2.6.0-cdh5.14.0</version></dependency><dependency><groupId>org.apache.Hadoop</groupId><artifactId>Hadoop-hdfs</artifactId><version>2.6.0-cdh5.14.0</version></dependency><dependency><groupId>org.apache.Hadoop</groupId><artifactId>Hadoop-mapreduce-client-core</artifactId><version>2.6.0-cdh5.14.0</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.11</version><scope>test</scope></dependency><dependency><groupId>org.testng</groupId><artifactId>testng</artifactId><version>RELEASE</version></dependency></dependencies><build><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.0</version><configuration><source>1.8</source><target>1.8</target><encoding>UTF-8</encoding></configuration></plugin><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-shade-plugin</artifactId><version>2.4.3</version><executions><execution><phase>package</phase><goals><goal>shade</goal></goals><configuration><minimizeJar>true</minimizeJar></configuration></execution></executions></plugin></plugins></build>
</project>

定义一个mapper类

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;import java.io.IOException;/*** @Author:Lenvo* @Description:* @Date: 2019-11-12 10:32*/
public class WordCountMap extends Mapper<LongWritable, Text, Text, LongWritable> {@Overrideprotected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {//key  指的是游戏中的编号//key代码里是   这行数据的偏移量//value   一串图形// value     zhangsan,lisi,wangwu//1   将value  从text转为StringString datas = value.toString();//2  切分数据    zhangsan            lisi        wangwuString[] splits = datas.split(",");//3 遍历输出/*   for (int i = 0; i < splits.length; i++) {}*/for (String data : splits) {//输出数据context.write(new Text(data), new LongWritable(1));}//zhangsan   1   输出一次（送一次）//lisi       1   输出一次（送一次）//wangwu     1   输出一次（送一次）}}

定义一个reducer类

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;import java.io.IOException;/*** @Author:Lenvo* @Description:* @Date: 2019-11-12 11:39*/
public class WordCountReduce extends Reducer<Text, LongWritable, Text, LongWritable> {//zhangsan   1,1,1,1//lisi       1,1,1@Overrideprotected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {//key  是游戏中的图形（zhangsan     lisi ）//values   好多  1long sum = 0;//遍历valuesfor (LongWritable value : values) {sum += value.get();}//输出context.write(key, new LongWritable(sum));}
}

定义一个主类，用来描述job并提交job

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;/*** @Author:Lenvo* @Description:* @Date: 2019-11-12 11:39*/
public class WordCountDriver extends Configured implements Tool {@Overridepublic int run(String[] args) throws Exception {//将已经编写好的Map    Reduce添加到计算框架中//1 、实例一个jobJob job = Job.getInstance(new Configuration(),"WordCount34");//2、使用job 设置读取数据(包括数据的路径)job.setInputFormatClass(TextInputFormat.class);TextInputFormat.addInputPath(job,new Path("F:\\aaa.txt"));//3、使用job 设置MAP类（map  输出的类型）job.setMapperClass(WordCountMap.class);job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(LongWritable.class);//4、使用job 设置Reduce类（Reduce 输入和输出的类型）job.setReducerClass(WordCountReduce.class);job.setOutputKeyClass(Text.class);job.setOutputValueClass(LongWritable.class);//5、使用job 设置数据的输出路径job.setOutputFormatClass(TextOutputFormat.class);TextOutputFormat.setOutputPath(job,new Path("F:\\BBB.txt"));//6、返回执行状态编号return job.waitForCompletion(true)?0:1;}//执行jobpublic static void main(String[] args) throws Exception {int run = ToolRunner.run(new WordCountDriver(), args);System.out.println(run);}}

点击执行 出现以下结果 执行成功

F:\ruanjian\Java\bin\java.exe "-javaagent:F:\ruanjian\IntelliJ IDEA 2018.3.5\lib\idea_rt.jar=52321:F:\ruanjian\IntelliJ IDEA 2018.3.5\bin" -Dfile.encoding=UTF-8 -classpath 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7.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\commons-beanutils\commons-beanutils-core\1.8.0\commons-beanutils-core-1.8.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\slf4j\slf4j-api\1.7.5\slf4j-api-1.7.5.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\slf4j\slf4j-log4j12\1.7.5\slf4j-log4j12-1.7.5.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\codehaus\jackson\jackson-core-asl\1.8.8\jackson-core-asl-1.8.8.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\codehaus\jackson\jackson-mapper-asl\1.8.8\jackson-mapper-asl-1.8.8.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\avro\avro\1.7.6-cdh5.14.0\avro-1.7.6-cdh5.14.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\thoughtworks\paranamer\paranamer\2.3\paranamer-2.3.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\xerial\snappy\snappy-java\1.0.4.1\snappy-java-1.0.4.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\google\protobuf\protobuf-java\2.5.0\protobuf-java-2.5.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\google\code\gson\gson\2.2.4\gson-2.2.4.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\hadoop\hadoop-auth\2.6.0-cdh5.14.0\hadoop-auth-2.6.0-cdh5.14.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\directory\server\apacheds-kerberos-codec\2.0.0-M15\apacheds-kerberos-codec-2.0.0-M15.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\directory\server\apacheds-i18n\2.0.0-M15\apacheds-i18n-2.0.0-M15.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\directory\api\api-asn1-api\1.0.0-M20\api-asn1-api-1.0.0-M20.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\directory\api\api-util\1.0.0-M20\api-util-1.0.0-M20.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\curator\curator-framework\2.7.1\curator-framework-2.7.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\jcraft\jsch\0.1.42\jsch-0.1.42.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\curator\curator-client\2.7.1\curator-client-2.7.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\curator\curator-recipes\2.7.1\curator-recipes-2.7.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\google\code\findbugs\jsr305\3.0.0\jsr305-3.0.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\htrace\htrace-core4\4.0.1-incubating\htrace-core4-4.0.1-incubating.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\zookeeper\zookeeper\3.4.5-cdh5.14.0\zookeeper-3.4.5-cdh5.14.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\commons\commons-compress\1.4.1\commons-compress-1.4.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\tukaani\xz\1.0\xz-1.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\commons-daemon\commons-daemon\1.0.13\commons-daemon-1.0.13.jar;F:\ruanjian\apache-maven-3.3.9\repository\io\netty\netty\3.10.5.Final\netty-3.10.5.Final.jar;F:\ruanjian\apache-maven-3.3.9\repository\io\netty\netty-all\4.0.23.Final\netty-all-4.0.23.Final.jar;F:\ruanjian\apache-maven-3.3.9\repository\xerces\xercesImpl\2.9.1\xercesImpl-2.9.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\xml-apis\xml-apis\1.3.04\xml-apis-1.3.04.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\fusesource\leveldbjni\leveldbjni-all\1.8\leveldbjni-all-1.8.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\hadoop\hadoop-mapreduce-client-core\2.6.0-cdh5.14.0\Hadoop-mapreduce-client-core-2.6.0-cdh5.14.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\hadoop\hadoop-yarn-common\2.6.0-cdh5.14.0\hadoop-yarn-common-2.6.0-cdh5.14.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\apache\hadoop\hadoop-yarn-api\2.6.0-cdh5.14.0\hadoop-yarn-api-2.6.0-cdh5.14.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\javax\xml\bind\jaxb-api\2.2.2\jaxb-api-2.2.2.jar;F:\ruanjian\apache-maven-3.3.9\repository\javax\xml\stream\stax-api\1.0-2\stax-api-1.0-2.jar;F:\ruanjian\apache-maven-3.3.9\repository\javax\activation\activation\1.1\activation-1.1.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\sun\jersey\jersey-client\1.9\jersey-client-1.9.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\google\inject\guice\3.0\guice-3.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\javax\inject\javax.inject\1\javax.inject-1.jar;F:\ruanjian\apache-maven-3.3.9\repository\aopalliance\aopalliance\1.0\aopalliance-1.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\sun\jersey\contribs\jersey-guice\1.9\jersey-guice-1.9.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\google\inject\extensions\guice-servlet\3.0\guice-servlet-3.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\org\testng\testng\7.0.0\testng-7.0.0.jar;F:\ruanjian\apache-maven-3.3.9\repository\com\beust\jcommander\1.72\jcommander-1.72.jar WordCountDriver
19/11/12 16:08:17 INFO Configuration.deprecation: session.id is deprecated. Instead, use dfs.metrics.session-id
19/11/12 16:08:17 INFO jvm.JvmMetrics: Initializing JVM Metrics with processName=JobTracker, sessionId=
19/11/12 16:08:17 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same.
19/11/12 16:08:17 WARN mapred.JobClient: No job jar file set.  User classes may not be found. See JobConf(Class) or JobConf#setJar(String).
19/11/12 16:08:17 INFO input.FileInputFormat: Total input paths to process : 1
19/11/12 16:08:17 INFO mapred.LocalJobRunner: OutputCommitter set in config null
19/11/12 16:08:17 INFO mapred.JobClient: Running job: job_local868986662_0001
19/11/12 16:08:17 INFO mapred.LocalJobRunner: OutputCommitter is org.apache.hadoop.mapreduce.lib.output.FileOutputCommitter
19/11/12 16:08:17 INFO mapred.LocalJobRunner: Waiting for map tasks
19/11/12 16:08:17 INFO mapred.LocalJobRunner: Starting task: attempt_local868986662_0001_m_000000_0
19/11/12 16:08:18 WARN mapreduce.Counters: Group org.apache.hadoop.mapred.Task$Counter is deprecated. Use org.apache.hadoop.mapreduce.TaskCounter instead
19/11/12 16:08:18 INFO mapred.Task:  Using ResourceCalculatorPlugin : null
19/11/12 16:08:18 INFO mapred.MapTask: Processing split: file:/F:/aaa.txt:0+73
19/11/12 16:08:18 INFO mapred.MapTask: Map output collector class = org.apache.hadoop.mapred.MapTask$MapOutputBuffer
19/11/12 16:08:18 INFO mapred.MapTask: io.sort.mb = 100
19/11/12 16:08:18 INFO mapred.MapTask: data buffer = 79691776/99614720
19/11/12 16:08:18 INFO mapred.MapTask: record buffer = 262144/327680
19/11/12 16:08:18 INFO mapred.LocalJobRunner: 
19/11/12 16:08:18 INFO mapred.MapTask: Starting flush of map output
19/11/12 16:08:18 INFO mapred.MapTask: Finished spill 0
19/11/12 16:08:18 INFO mapred.Task: Task:attempt_local868986662_0001_m_000000_0 is done. And is in the process of commiting
19/11/12 16:08:18 INFO mapred.LocalJobRunner: 
19/11/12 16:08:18 INFO mapred.Task: Task 'attempt_local868986662_0001_m_000000_0' done.
19/11/12 16:08:18 INFO mapred.LocalJobRunner: Finishing task: attempt_local868986662_0001_m_000000_0
19/11/12 16:08:18 INFO mapred.LocalJobRunner: Map task executor complete.
19/11/12 16:08:18 WARN mapreduce.Counters: Group org.apache.hadoop.mapred.Task$Counter is deprecated. Use org.apache.hadoop.mapreduce.TaskCounter instead
19/11/12 16:08:18 INFO mapred.Task:  Using ResourceCalculatorPlugin : null
19/11/12 16:08:18 INFO mapred.LocalJobRunner: 
19/11/12 16:08:18 INFO mapred.Merger: Merging 1 sorted segments
19/11/12 16:08:18 INFO mapred.Merger: Down to the last merge-pass, with 1 segments left of total size: 193 bytes
19/11/12 16:08:18 INFO mapred.LocalJobRunner: 
19/11/12 16:08:18 INFO mapred.Task: Task:attempt_local868986662_0001_r_000000_0 is done. And is in the process of commiting
19/11/12 16:08:18 INFO mapred.LocalJobRunner: 
19/11/12 16:08:18 INFO mapred.Task: Task attempt_local868986662_0001_r_000000_0 is allowed to commit now
19/11/12 16:08:18 INFO output.FileOutputCommitter: Saved output of task 'attempt_local868986662_0001_r_000000_0' to F:/BBB.txt
19/11/12 16:08:18 INFO mapred.LocalJobRunner: reduce > reduce
19/11/12 16:08:18 INFO mapred.Task: Task 'attempt_local868986662_0001_r_000000_0' done.
19/11/12 16:08:18 INFO mapred.JobClient:  map 100% reduce 100%
19/11/12 16:08:18 INFO mapred.JobClient: Job complete: job_local868986662_0001
19/11/12 16:08:18 INFO mapred.JobClient: Counters: 17
19/11/12 16:08:18 INFO mapred.JobClient:   File System Counters
19/11/12 16:08:18 INFO mapred.JobClient:     FILE: Number of bytes read=613
19/11/12 16:08:18 INFO mapred.JobClient:     FILE: Number of bytes written=339766
19/11/12 16:08:18 INFO mapred.JobClient:     FILE: Number of read operations=0
19/11/12 16:08:18 INFO mapred.JobClient:     FILE: Number of large read operations=0
19/11/12 16:08:18 INFO mapred.JobClient:     FILE: Number of write operations=0
19/11/12 16:08:18 INFO mapred.JobClient:   Map-Reduce Framework
19/11/12 16:08:18 INFO mapred.JobClient:     Map input records=4
19/11/12 16:08:18 INFO mapred.JobClient:     Map output records=12
19/11/12 16:08:18 INFO mapred.JobClient:     Map output bytes=167
19/11/12 16:08:18 INFO mapred.JobClient:     Input split bytes=81
19/11/12 16:08:18 INFO mapred.JobClient:     Combine input records=0
19/11/12 16:08:18 INFO mapred.JobClient:     Combine output records=0
19/11/12 16:08:18 INFO mapred.JobClient:     Reduce input groups=9
19/11/12 16:08:18 INFO mapred.JobClient:     Reduce shuffle bytes=0
19/11/12 16:08:18 INFO mapred.JobClient:     Reduce input records=12
19/11/12 16:08:18 INFO mapred.JobClient:     Reduce output records=9
19/11/12 16:08:18 INFO mapred.JobClient:     Spilled Records=24
19/11/12 16:08:18 INFO mapred.JobClient:     Total committed heap usage (bytes)=514850816
0Process finished with exit code 0

最后在保存路径中查看

用代码编辑器中打开查看 可看到以下结果

MapReduce初体验结束

注意出现这个错误时 说明保存路径中已有计算结果的文件 不可再次保存（因为不支持覆盖）