Java实现MapReduce Wordcount案例
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先改pom.xml:
<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.mcq</groupId> <artifactId>mr-1101</artifactId> <version>0.0.1-SNAPSHOT</version> <dependencies> <dependency> <groupId>jdk.tools</groupId> <artifactId>jdk.tools</artifactId> <version>1.8</version> <scope>system</scope> <systemPath>${JAVA_HOME}/lib/tools.jar</systemPath> </dependency> <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> </project>
在resources文件夹下添加文件 log4j.properties:
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
WordcountDriver.java:
package com.mcq; 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 { System.out.println("hello"); 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类型 job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(IntWritable.class); //5.设置最终输出的key和value类型 job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); //6.设置输入路径和输出路径 FileInputFormat.setInputPaths(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); //7.提交Job // job.submit(); job.waitForCompletion(true); // boolean res=job.waitForCompletion(true);//true表示打印结果 // System.exit(res?0:1); } }
WordcountMapper.java:
package com.mcq; 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; //map阶段 //KEYIN:输入数据的key(偏移量,比如第一行是0~19,第二行是20~25),必须是LongWritable //VALUEIN:输入数据的value(比如文本内容是字符串,那就填Text) //KEYOUT:输出数据的key类型 //VALUEOUT:输出数据的值类型 public class WordcountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{ IntWritable v=new IntWritable(1); Text k = new Text(); @Override protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, IntWritable>.Context context) throws IOException, InterruptedException { // TODO Auto-generated method stub //1.获取一行 String line=value.toString(); //2.切割单词 String[] words=line.split(" "); //3.循环写出 for(String word:words) { k.set(word); context.write(k, v); } } }
WordcountReducer.java:
package com.mcq; import java.io.IOException; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Reducer; //KEYIN、VALUEIN:map阶段输出的key和value类型 public class WordcountReducer extends Reducer<Text, IntWritable, Text, IntWritable>{ IntWritable v=new IntWritable(); @Override protected void reduce(Text key, Iterable<IntWritable> values, Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException { // TODO Auto-generated method stub int sum=0; for(IntWritable value:values) { sum+=value.get(); } v.set(sum); context.write(key, v); } }
在run configuration里加上参数e:/mrtest/in.txt e:/mrtest/out.txt
运行时遇到了个bug,参考https://blog.csdn.net/qq_40310148/article/details/86617512解决了
在集群上运行:
用maven打成jar包,需要添加一些打包依赖:
<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.mcq.WordcountDriver</mainClass> </manifest> </archive> </configuration> <executions> <execution> <id>make-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> </execution> </executions> </plugin> </plugins> </build>
注意上面mainClass里要填驱动类的主类名,可以点击类名右键copy qualified name。
将程序打成jar包(具体操作:右键工程名run as maven install,然后target文件夹会产生两个jar包,我们把不用依赖的包拷贝到hadoop集群上,因为集群已经配好相关依赖了),上传到集群
输入以下命令运行
hadoop jar mr-1101-0.0.1-SNAPSHOT.jar com.mcq.WordcountDriver /xiaocao.txt /output
注意这里输入输出的路径是集群上的路径。
l>原文:https://www.cnblogs.com/mcq1999/p/11780758.html
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