彷徨 | MapReduce实例五 | MapReduce求TopN的三种方法 , 以电影数据为例

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本文采用三种方式对movie数据进行TopN排序
第一种是直接排序,在ReduceTask中进行排序
第二种是利用Tree排序,该方式利用小顶堆和集合重复原理的方式 , 每过来一个数据 , 跟堆顶数据进行比较 , 如果比最小的大 , 则 =踢掉换新的 , 否则直接跳过数据 . 以此对数据进行排序 . 
第三种是利用MepReduce高级API编程,定义分区器和分组比较器.

---

数据样本:

{"movie":"1193","rate":"5","timeStamp":"978300760","uid":"1"}
{"movie":"661","rate":"3","timeStamp":"978302109","uid":"1"}
{"movie":"914","rate":"3","timeStamp":"978301968","uid":"1"}
{"movie":"3408","rate":"4","timeStamp":"978300275","uid":"1"}
{"movie":"2355","rate":"5","timeStamp":"978824291","uid":"1"}
{"movie":"1197","rate":"3","timeStamp":"978302268","uid":"1"}
{"movie":"1287","rate":"5","timeStamp":"978302039","uid":"1"}
{"movie":"2804","rate":"5","timeStamp":"978300719","uid":"1"}
{"movie":"594","rate":"4","timeStamp":"978302268","uid":"1"}
{"movie":"919","rate":"4","timeStamp":"978301368","uid":"1"}
{"movie":"595","rate":"5","timeStamp":"978824268","uid":"1"}
{"movie":"938","rate":"4","timeStamp":"978301752","uid":"1"}
{"movie":"2398","rate":"4","timeStamp":"978302281","uid":"1"}
{"movie":"2918","rate":"4","timeStamp":"978302124","uid":"1"}

分析结果 : 以Top2为例

MovieBean [movie=1, rate=5, timeStamp=959639915, uid=5524]
MovieBean [movie=1, rate=5, timeStamp=966904109, uid=3527]
MovieBean [movie=10, rate=5, timeStamp=971922432, uid=2899]
MovieBean [movie=10, rate=5, timeStamp=975867811, uid=606]
MovieBean [movie=100, rate=5, timeStamp=964115248, uid=4626]
MovieBean [movie=100, rate=5, timeStamp=965387978, uid=4277]
MovieBean [movie=1000, rate=5, timeStamp=976240118, uid=474]
MovieBean [movie=1000, rate=5, timeStamp=966468743, uid=3644]
MovieBean [movie=1002, rate=5, timeStamp=962597546, uid=4981]
MovieBean [movie=1002, rate=5, timeStamp=965314044, uid=4225]
MovieBean [movie=1003, rate=5, timeStamp=974698008, uid=1908]
MovieBean [movie=1003, rate=5, timeStamp=963248386, uid=4745]
MovieBean [movie=1004, rate=5, timeStamp=965581802, uid=3997]
MovieBean [movie=1004, rate=5, timeStamp=957671549, uid=5862]

---

方式一 : 

直接利用MapReduce框架做 , 在ReduceTask中进行排序 , 也是最简单的一种 . 该方式的核心代码就是Reduce里面的排序代码

代码实现:

1 . MovieBean

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.Writable;
/**
 * Writable hadoop 序列化接口
 * @author root
 *
 */
public class MovieBean implements Writable{
	//{"movie":"1193","rate":"5","timeStamp":"978300760","uid":"1"}
	private String movie;
	private int rate;
	private String timeStamp;
	private String uid;
	@Override
	public void write(DataOutput out) throws IOException {
		out.writeUTF(movie);
		out.writeInt(rate);
		out.writeUTF(timeStamp);
		out.writeUTF(uid);
		
	}
	@Override
	public void readFields(DataInput in) throws IOException {
		movie = in.readUTF();
		rate = in.readInt();
		timeStamp = in.readUTF();
		uid = in.readUTF();
	}
	
	
	public String getMovie() {
		return movie;
	}
	public void setMovie(String movie) {
		this.movie = movie;
	}
	public int getRate() {
		return rate;
	}
	public void setRate(int rate) {
		this.rate = rate;
	}
	public String getTimeStamp() {
		return timeStamp;
	}
	public void setTimeStamp(String timeStamp) {
		this.timeStamp = timeStamp;
	}
	public String getUid() {
		return uid;
	}
	public void setUid(String uid) {
		this.uid = uid;
	}
	@Override
	public String toString() {
		return "MovieBean [movie=" + movie + ", rate=" + rate + ", timeStamp=" + timeStamp + ", uid=" + uid + "]";
	}
	public void set(MovieBean movieBean) {
		this.movie = movieBean.getMovie();
		this.rate = movieBean.getRate();
		this.timeStamp = movieBean.getTimeStamp();
		this.uid = movieBean.getUid();
		
	}
	public void set(String string, int i, String string2, String string3) {
		// TODO Auto-generated method stub
		
	}

}

2 . TopN1

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.apache.commons.io.FileUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import com.alibaba.fastjson.JSON;


public class TopN1 {
	public static class MapTask extends Mapper<LongWritable, Text, Text, MovieBean>{
		@Override
		protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, MovieBean>.Context context)
				throws IOException, InterruptedException {
			try {
				MovieBean movieBean = JSON.parseObject(value.toString(), MovieBean.class);
				String movie = movieBean.getMovie();
				context.write(new Text(movie), movieBean);
			} catch (Exception e) {
				
			}
		}
	}
	
	public static class ReduceTask extends Reducer<Text, MovieBean, MovieBean, NullWritable>{
		@Override
		protected void reduce(Text movieId, Iterable<MovieBean> movieBeans,
				Reducer<Text, MovieBean, MovieBean, NullWritable>.Context context)
				throws IOException, InterruptedException {
			List<MovieBean> list = new ArrayList<>();
			
			for (MovieBean movieBean : movieBeans) {
				MovieBean movieBean2 = new MovieBean();
				movieBean2.set(movieBean);
				list.add(movieBean2);//????
			}
			Collections.sort(list, new Comparator<MovieBean>() {

				@Override
				public int compare(MovieBean o1, MovieBean o2) {
					
					return o2.getRate() - o1.getRate();
				}
			});
			for (int i = 0; i < Math.min(20, list.size()); i++) {
				context.write(list.get(i), NullWritable.get());
			}
		}
	}
	
	public static void main(String[] args) throws Exception{
		Configuration conf = new Configuration();
		
		Job job = Job.getInstance(conf, "avg");
		
		//设置map和reduce，以及提交的jar
		job.setMapperClass(MapTask.class);
		job.setReducerClass(ReduceTask.class);
		job.setJarByClass(TopN1.class);
		
		//设置输入输出类型
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(MovieBean.class);
		
		job.setOutputKeyClass(MovieBean.class);
		job.setOutputValueClass(NullWritable.class);
		
		//输入和输出目录
		FileInputFormat.addInputPath(job, new Path("E:/data/rating.json"));
		FileOutputFormat.setOutputPath(job, new Path("E:\\data\\out\\topN1"));
		
		//判断文件是否存在
		File file = new File("E:\\data\\out\\topN1");
		if(file.exists()){
			FileUtils.deleteDirectory(file);
		}
		
		//提交任务
		boolean completion = job.waitForCompletion(true);
		System.out.println(completion?"你很优秀！！！":"滚去调bug！！");
		
	}
	

}

---

方式二 : 

该方式利用小顶堆和集合重复原理的方式 , 每过来一个数据 , 跟堆顶数据进行比较 , 如果比最小的大 , 则 =踢掉换新的 , 否则直接跳过数据 . 以此对数据进行排序 . 

代码实现 : 

1 . MovieBean同上

2.TopN2

package hadoop_day06.zhang.movieTopn.N2;

import java.io.File;
import java.io.IOException;
import java.util.Comparator;
import java.util.TreeSet;

import org.apache.commons.io.FileUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import com.alibaba.fastjson.JSON;

public class TopN2 {

	public static class MapTask extends Mapper<LongWritable, Text, Text, MovieBean>{
		
		@Override
		protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, MovieBean>.Context context)
				throws IOException, InterruptedException {
			try {
				MovieBean movieBean = JSON.parseObject(value.toString(), MovieBean.class);
				String movie = movieBean.getMovie();
				context.write(new Text(movie), movieBean);
			} catch (Exception e) {
				// TODO: handle exception
			}
		}
	}
	
	public static class ReduceTask extends Reducer<Text, MovieBean, MovieBean, NullWritable>{
		@Override
		protected void reduce(Text movieId, Iterable<MovieBean> movieBeans,
				Reducer<Text, MovieBean, MovieBean, NullWritable>.Context context)
				throws IOException, InterruptedException {
			TreeSet<MovieBean> tree = new TreeSet<>(new Comparator<MovieBean>() {

				@Override
				public int compare(MovieBean o1, MovieBean o2) {
					if (o1.getRate() - o2.getRate() == 0) {
						return o1.getUid().compareTo(o2.getUid());
					} else {
						return o1.getRate() - o2.getRate();
					}
				}
			});
			for (MovieBean movieBean : movieBeans) {
				MovieBean movieBean2 = new MovieBean();
				movieBean2.set(movieBean);
				if (tree.size() <= 2) {
					tree.add(movieBean2);
				} else {
					MovieBean first = tree.first();
					if(first.getRate() < movieBean2.getRate()) {
						//做替换
						tree.remove(first);
						tree.add(movieBean2);
					}
				}
			}
			for (MovieBean movieBean : tree) {
				context.write(movieBean, NullWritable.get());
			}
		}
		
	}
	
	public static void main(String[] args) throws Exception{
		Configuration conf = new Configuration();
		
		Job job = Job.getInstance(conf, "topN2");
		
		//设置map和reduce，以及提交的jar
		job.setMapperClass(MapTask.class);
		job.setReducerClass(ReduceTask.class);
		job.setJarByClass(TopN2.class);
		
		//设置输入输出类型
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(MovieBean.class);
		
		job.setOutputKeyClass(MovieBean.class);
		job.setOutputValueClass(NullWritable.class);
		
		//输入和输出目录
		FileInputFormat.addInputPath(job, new Path("E:/data/rating.json"));
		FileOutputFormat.setOutputPath(job, new Path("E:\\data\\out\\topN2"));
		
		//判断文件是否存在
		File file = new File("E:\\data\\out\\topN2");
		if(file.exists()){
			FileUtils.deleteDirectory(file);
		}
		
		//提交任务
		boolean completion = job.waitForCompletion(true);
		System.out.println(completion?"你很优秀！！！":"滚去调bug！！");
		
	}
}

运行结果 : 

MovieBean [movie=1, rate=5, timeStamp=968563309, uid=3205]
MovieBean [movie=1, rate=5, timeStamp=966904109, uid=3527]
MovieBean [movie=1, rate=5, timeStamp=959639915, uid=5524]
MovieBean [movie=10, rate=5, timeStamp=976898286, uid=1329]
MovieBean [movie=10, rate=5, timeStamp=971922432, uid=2899]
MovieBean [movie=10, rate=5, timeStamp=975867811, uid=606]
MovieBean [movie=100, rate=5, timeStamp=966291689, uid=3700]
MovieBean [movie=100, rate=5, timeStamp=965387978, uid=4277]
MovieBean [movie=100, rate=5, timeStamp=964115248, uid=4626]
MovieBean [movie=1000, rate=4, timeStamp=968541342, uid=3224]
MovieBean [movie=1000, rate=5, timeStamp=966468743, uid=3644]
MovieBean [movie=1000, rate=5, timeStamp=976240118, uid=474]
MovieBean [movie=1002, rate=5, timeStamp=974833560, uid=1242]
MovieBean [movie=1002, rate=5, timeStamp=965314044, uid=4225]
MovieBean [movie=1002, rate=5, timeStamp=962597546, uid=4981]
MovieBean [movie=1003, rate=5, timeStamp=974698008, uid=1908]
MovieBean [movie=1003, rate=5, timeStamp=965710118, uid=3927]
MovieBean [movie=1003, rate=5, timeStamp=963248386, uid=4745]
MovieBean [movie=1004, rate=5, timeStamp=965581802, uid=3997]
MovieBean [movie=1004, rate=5, timeStamp=962936941, uid=4807]
MovieBean [movie=1004, rate=5, timeStamp=957671549, uid=5862]
MovieBean [movie=1005, rate=5, timeStamp=970346351, uid=3032]
MovieBean [movie=1005, rate=5, timeStamp=964461162, uid=4572]
MovieBean [movie=1005, rate=5, timeStamp=964036670, uid=4633]

---

方式三 : 

利用MR编程框架中的高级API

要用自定义类型Bean作为map输出的KEY，则需要以下编程接口：

Bean 必须实现  WritableComparable 接口：   write()  readFields()   compareTo()

分区器：必须自定义一个分区器：

XPartitioner extends Partitioner<KEY,VALUE>，核心方法：getPartition(KEY k,VALUE v,int numReduceTasks)

分组比较器：必须自定义一个分组比较器

XGroupingComparator  extends WritableComparator{
    public XGroupingComparator(){
        super(key.class,true);
    }
    compare(WritableComparable a,WritableComparable b){
    
    };
}

代码实现 : 

1 . movieBean

package hadoop_day06.zhang.movieTopn.N3;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.WritableComparable;

/**
 * Writeable  hadoop的序列化接口
 * 能够排序
 * @author Administrator
 *
 */


public class MovieBean implements WritableComparable<MovieBean>{
	//{"movie":"1193","rate":"5","timeStamp":"978300760","uid":"1"}
	private String movie;
	private int rate;
	private String timeStamp;
	private String uid;

	@Override
	public int compareTo(MovieBean o) {
		if(o.getMovie().compareTo(this.getMovie())==0){
			return o.getRate() - this.getRate();
		}else{
			return o.getMovie().compareTo(this.getMovie());
		}
		//return 0;
	}
	
	public void set(String movie,int rate,String timeStamp,String uid){
		this.movie = movie;
		this.rate = rate;
		this.timeStamp = timeStamp;
		this.uid = uid;
	}
	
	@Override
	public void write(DataOutput out) throws IOException {
		out.writeUTF(movie);
		out.writeInt(rate);
		out.writeUTF(timeStamp);
		out.writeUTF(uid);
		
	}
	@Override
	public void readFields(DataInput in) throws IOException {
		movie = in.readUTF();
		rate = in.readInt();
		timeStamp = in.readUTF();
		uid = in.readUTF();
	}
	
	
	public String getMovie() {
		return movie;
	}
	public void setMovie(String movie) {
		this.movie = movie;
	}
	public int getRate() {
		return rate;
	}
	public void setRate(int rate) {
		this.rate = rate;
	}
	public String getTimeStamp() {
		return timeStamp;
	}
	public void setTimeStamp(String timeStamp) {
		this.timeStamp = timeStamp;
	}
	public String getUid() {
		return uid;
	}
	public void setUid(String uid) {
		this.uid = uid;
	}
	@Override
	public String toString() {
		return "MovieBean [movie=" + movie + ", rate=" + rate + ", timeStamp=" + timeStamp + ", uid=" + uid + "]";
	}
	public void set(MovieBean movieBean) {
		this.movie = movieBean.getMovie();
		this.rate = movieBean.getRate();
		this.timeStamp = movieBean.getTimeStamp();
		this.uid = movieBean.getUid();
		
	}

}

2 . MyPartition

package hadoop_day06.zhang.movieTopn.N3;

import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.Partitioner;

/**
 * 分区的：
 * 把想要的数据分到相同的reduce里面
 * @author root
 *
 */
public class MyPartition extends Partitioner<MovieBean, NullWritable>{
	/**
	 * munPartitions 代表有多少个reducetask
	 * key map端输出的key
	 * value map端输出的value
	 */
	@Override
	public int getPartition(MovieBean key, NullWritable value, int numPartitions) {
		return (key.getMovie().hashCode() & Integer.MAX_VALUE)%numPartitions;
	}

}

3 . MyGroup

package hadoop_day06.zhang.movieTopn.N3;

import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
/**
 * 分组：movieid相同的分到一起
 * @author root
 *
 */
public class MyGroup extends WritableComparator{
	
	public MyGroup() {
		super(MovieBean.class,true);
	}
	
	@SuppressWarnings("rawtypes")
	@Override
	public int compare(WritableComparable a, WritableComparable b) {
		MovieBean bean1 = (MovieBean)a;
		MovieBean bean2 = (MovieBean)b;
		return bean1.getMovie().compareTo(bean2.getMovie());
	}

}

4 . TopN3

package hadoop_day06.zhang.movieTopn.N3;

import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.codehaus.jackson.map.ObjectMapper;


public class TopN3 {
	public static class MapTask extends Mapper<LongWritable, Text, MovieBean, NullWritable>{
		
		@Override
		protected void map(LongWritable key, Text value,
				Mapper<LongWritable, Text, MovieBean, NullWritable>.Context context)
				throws IOException, InterruptedException {
			try {
				ObjectMapper mapper = new ObjectMapper();
				MovieBean bean = mapper.readValue(value.toString(), MovieBean.class);
				context.write(bean, NullWritable.get());
			} catch (Exception e) {
				// TODO: handle exception
			}
		}
	}
	
	public static class ReduceTask extends Reducer<MovieBean, NullWritable, MovieBean, NullWritable>{
		@SuppressWarnings("unused")
		@Override
		protected void reduce(MovieBean key, Iterable<NullWritable> values,
				Reducer<MovieBean, NullWritable, MovieBean, NullWritable>.Context context)
				throws IOException, InterruptedException {
			int num = 0;
			//虽然是一个空的，但是key能够根据迭代进行相应的得到对应空值的结果
			for (NullWritable nullWritable : values) {
				if(num>=2){
					break;
				}
				num++;
				context.write(key, NullWritable.get());
			}
		}
	}
	
	public static void main(String[] args) throws Exception{
		Configuration conf = new Configuration();
		
		Job job = Job.getInstance(conf, "topn3");
		
		//设置map和reduce，以及提交的jar
		job.setMapperClass(MapTask.class);
		job.setReducerClass(ReduceTask.class);
		job.setJarByClass(TopN3.class);
		//job.setNumReduceTasks(2);
		job.setPartitionerClass(MyPartition.class);
		job.setGroupingComparatorClass(MyGroup.class);
		
		
		//设置输入输出类型
		job.setMapOutputKeyClass(MovieBean.class);
		job.setMapOutputValueClass(NullWritable.class);
		
		job.setOutputKeyClass(MovieBean.class);
		job.setOutputValueClass(NullWritable.class);
		
		//输入和输出目录
		FileInputFormat.addInputPath(job, new Path("E:/data/rating.json"));
		FileOutputFormat.setOutputPath(job, new Path("E:\\data\\out\\topN3"));
		
		//判断文件是否存在
		File file = new File("E:\\data\\out\\topN3");
		if(file.exists()){
			FileUtils.deleteDirectory(file);
		}
		
		//提交任务
		boolean completion = job.waitForCompletion(true);
		System.out.println(completion?"你很优秀！！！":"滚去调bug！！");
	}
}

运行结果 : 只截取一段

MovieBean [movie=999, rate=5, timeStamp=967983748, uid=3842]
MovieBean [movie=999, rate=5, timeStamp=972348071, uid=5317]
MovieBean [movie=998, rate=5, timeStamp=974731896, uid=1825]
MovieBean [movie=998, rate=5, timeStamp=970350907, uid=3032]
MovieBean [movie=997, rate=5, timeStamp=967397690, uid=3418]
MovieBean [movie=997, rate=5, timeStamp=965242917, uid=4557]
MovieBean [movie=996, rate=5, timeStamp=971903343, uid=2900]
MovieBean [movie=996, rate=5, timeStamp=976490369, uid=306]
MovieBean [movie=994, rate=5, timeStamp=959456139, uid=5553]
MovieBean [movie=994, rate=5, timeStamp=968002575, uid=3305]
MovieBean [movie=993, rate=5, timeStamp=970048313, uid=4277]
MovieBean [movie=993, rate=4, timeStamp=984153990, uid=331]
MovieBean [movie=992, rate=5, timeStamp=963976969, uid=4645]
MovieBean [movie=992, rate=4, timeStamp=966033503, uid=3868]
MovieBean [movie=991, rate=5, timeStamp=975900929, uid=593]
MovieBean [movie=991, rate=5, timeStamp=977243479, uid=1501]
MovieBean [movie=990, rate=4, timeStamp=965294965, uid=4277]
MovieBean [movie=990, rate=4, timeStamp=967071268, uid=3491]
MovieBean [movie=99, rate=5, timeStamp=959938819, uid=5452]
MovieBean [movie=99, rate=5, timeStamp=974762428, uid=1408]
MovieBean [movie=989, rate=5, timeStamp=974693867, uid=1915]
MovieBean [movie=988, rate=5, timeStamp=974738718, uid=1587]
MovieBean [movie=988, rate=5, timeStamp=971769566, uid=2913]