简述
Partitioner组件可以让Map对Key进行分区，从而可以根据不同的key来分发到不同的reduce中去处理；
你可以自定义key的一个分发规则，如数据文件包含不同的大学，而输出的要求是每个大学输出一个文件；
Partitioner组件提供了一个默认的HashPartitioner。
package org.apache.hadoop.mapreduce.lib.partition;
public class HashPartitioner<K, V> extends Partitioner<K, V> {
/** Use {@link Object#hashCode()} to partition. */
public int getPartition(K key, V value,
int numReduceTasks) {
return (key.hashCode() & Integer.MAX_VALUE) % numReduceTasks;
}
}自定义Partitioner
1、继承抽象类Partitioner，实现自定义的getPartition()方法；
2、通过job.setPartitionerClass(...)来设置自定义的Partitioner；
Partitioner类
package org.apache.hadoop.mapreduce;
public abstract class Partitioner<KEY, VALUE> {
/**
* Get the partition number for a given key (hence record) given the total
* number of partitions i.e. number of reduce-tasks for the job.
*
* <p>Typically a hash function on a all or a subset of the key.</p>
*
* @param key the key to be partioned.
* @param value the entry value.
* @param numPartitions the total number of partitions.
* @return the partition number for the <code>key</code>.
*/
public abstract int getPartition(KEY key, VALUE value, int numPartitions);
}Partitioner应用场景及实例
需求：分别统计每种商品的周销售情况
address1的周销售清单（input1）：
shoes 20
hat 10
stockings 30
clothes 40
address2的周销售清单（input2）：
shoes 15
hat 1
stockings 90
clothes 80
汇总结果（output）：
shoes 35
hat 11
stockings 120
clothes 120
package MyPartitioner;
import java.io.IOException;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class MyPartitioner {
private final static String INPUT_PATH = "hdfs://liguodong:8020/input";
private final static String OUTPUT_PATH = "hdfs://liguodong:8020/output";
public static class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable>{
private Text word = new Text();
private IntWritable one = new IntWritable();
@Override
protected void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String[] str = value.toString().split("\\s+");
word.set(str[0]);
one.set(Integer.parseInt(str[1]));
context.write(word, one);
}
}
public static class MyReducer extends Reducer<Text, IntWritable,Text, IntWritable>{
private IntWritable result = new IntWritable();
@Override
protected void reduce(Text key, Iterable<IntWritable> values,
Context context)
throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum+=val.get();
}
result.set(sum);
context.write(key,result);
}
}
public static class DefPartitioner extends Partitioner<Text,IntWritable>{
@Override
public int getPartition(Text key, IntWritable value, int numPartitions) {
if(key.toString().equals("shoes")){
return 0;
}else if(key.toString().equals("hat")){
return 1;
}else if(key.toString().equals("stockings")){
return 2;
}else{
return 3;
}
}
}
public static void main(String[] args) throws Exception {
//1、配置
Configuration conf = new Configuration();
final FileSystem fileSystem = FileSystem.get(new URI(INPUT_PATH),conf);
if(fileSystem.exists(new Path(OUTPUT_PATH)))
{
fileSystem.delete(new Path(OUTPUT_PATH),true);
}
Job job = Job.getInstance(conf, "define partitioner");
//2、打包运行必须执行的方法
job.setJarByClass(MyPartitioner.class);
//3、输入路径
FileInputFormat.addInputPath(job, new Path(INPUT_PATH));
//4、Map
job.setMapperClass(MyMapper.class);
//5、Combiner
//job.setCombinerClass(MyReducer.class);
job.setPartitionerClass(DefPartitioner.class);
//6、Reducer
job.setReducerClass(MyReducer.class);
job.setNumReduceTasks(4);//reduce个数默认是1
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
//7、 输出路径
FileOutputFormat.setOutputPath(job, new Path(OUTPUT_PATH));
//8、提交作业
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}[[email protected] file]# hdfs dfs -mkdir /input
上传文件
[[email protected] file]# hdfs dfs -put input1 /input/
[[email protected] file]# hdfs dfs -put input2 /input/
[[email protected] file]# hdfs dfs -ls /input/
Found 2 items
-rw-r--r-- 1 root supergroup 52 2015-06-14 10:22 /input/input1
-rw-r--r-- 1 root supergroup 50 2015-06-14 10:22 /input/input2
打成jar包，然后执行。
[[email protected] file]# jar tf partitioner.jar
META-INF/MANIFEST.MF
MyPartitioner/MyPartitioner$DefPartitioner.class
MyPartitioner/MyPartitioner$MyMapper.class
MyPartitioner/MyPartitioner$MyReducer.class
MyPartitioner/MyPartitioner.class
[[email protected] file]# yarn jar partitioner.jar
输出结果
[[email protected] file]# hdfs dfs -ls /output/
Found 5 items
-rw-r--r-- 1 root supergroup 0 2015-06-14 11:08 /output/_SUCCESS
-rw-r--r-- 1 root supergroup 9 2015-06-14 11:08 /output/part-r-00000
-rw-r--r-- 1 root supergroup 7 2015-06-14 11:08 /output/part-r-00001
-rw-r--r-- 1 root supergroup 0 2015-06-14 11:08 /output/part-r-00002
-rw-r--r-- 1 root supergroup 26 2015-06-14 11:08 /output/part-r-00003
[[email protected] file]# hdfs dfs -cat /output/part-r-00000
shoes 35
[[email protected] file]# hdfs dfs -cat /output/part-r-00001
hat 11
[[email protected] file]# hdfs dfs -cat /output/part-r-00002
stockings 120
[[email protected] file]# hdfs dfs -cat /output/part-r-00003
clothes 120
时间： 2024-08-28 18:31:03