原文地址:http://chenxiaoqiong.com/articles/mapreduce2/
看了 MapReduce实例(一),应该对mapreduce有了基本了解,试着自己去实现下面的例子,相信你会有收获的。
实例需求
将输入文件中的数字进行排序,要求输出文件中输出序号、数字。
输入文件
1
999
24
12
45
输出文件
1 1
2 12
3 24
4 45
5 999
设计思路
熟悉MapReduce过程的读者会很快想到在MapReduce过程中就有排序,我们可以利用IntWritable排序规则,map按数字大小对key进行排序,reduce拿到key,循环value-list之后,将行号作为序号,输入的key作为value输出。
代码实现
代码已上传至我的git:https://github.com/chenxiaoqiong/sortMapReduce
主要代码:
/**
* <h1> MapReduce实例(二) </h1>
* SortMapReduce:对输入数字进行排序输出
* Created by chenxiaoqiong on 2017/3/27 0017 下午 2:14.
*/
public class SortMapReduce extends Configured implements Tool {
/**
* map:处理输入文件:按输入数字排序输出(数字 1)
*/
public static class SortMapper
extends Mapper<LongWritable, Text, IntWritable, IntWritable> {
private final static IntWritable ints = new IntWritable(1);
private IntWritable keyword = new IntWritable();
@Override
protected void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String line=value.toString();
keyword.set(Integer.parseInt(line));
// void write(KEYOUT var1, VALUEOUT var2) 此方法会按KEYOUT var1自动排序
context.write(keyword, ints);
}
}
/**
* reduce:输出序号和map排序好的数字(序号 数字)
*/
public static class SortReducer
extends Reducer<IntWritable, IntWritable, IntWritable, IntWritable> {
private IntWritable linenum = new IntWritable(1);
@Override
protected void reduce(IntWritable key, Iterable<IntWritable> value, Context context)
throws IOException, InterruptedException {
for(IntWritable val:value){
context.write(linenum, key);
linenum = new IntWritable(linenum.get()+1);
}
}
}
public int run(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
//获取配置文件:
Configuration conf = super.getConf();
//创建job:
Job job = Job.getInstance(conf, this.getClass().getSimpleName());
job.setJarByClass(SortMapReduce.class);
//配置作业:
// Input --> Map --> Reduce --> Output
// Input:
Path inPath = new Path(args[0]);
FileInputFormat.addInputPath(job, inPath);
//FileInputFormat过程会将文件处理(Format)成 <偏移量,每一行内容> 的key value对。
//Map 设置Mapper类,设置Mapper类输出的Key、Value的类型:
job.setMapperClass(SortMapper.class);
job.setMapOutputKeyClass(IntWritable.class);
job.setMapOutputValueClass(IntWritable.class);
//Reduce 设置Reducer类, 设置最终输出的 Key、Value的类型(setOutputKeyClass、setOutputValueClass):
job.setReducerClass(SortReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
//Output 设置输出路径
Path outPath = new Path(args[1]);
FileOutputFormat.setOutputPath(job, outPath);
//提交任务
boolean isSucess = job.waitForCompletion(true);
return isSucess ? 1 : 0; //成功返回1 ,失败返回0
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
int status = ToolRunner.run(conf, new SortMapReduce(), args);
System.exit(status);
}
}
pom.xml
<?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>hadoop</groupId>
<artifactId>countMapReduce</artifactId>
<version>1.0-SNAPSHOT</version>
<repositories>
<repository>
<id>apache</id>
<url>http://maven.apache.org</url>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>2.7.3</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>2.7.3</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>2.7.3</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-core</artifactId>
<version>1.2.1</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
<configuration>
<excludeTransitive>false</excludeTransitive>
<stripVersion>true</stripVersion>
<outputDirectory>./lib</outputDirectory>
</configuration>
</plugin>
</plugins>
</build>
</project>