一、定義好友檔案qq

hadoop hello
hdfs world
tom cat
cat dog
hello world
hello hdfs

hadoop好友hello，hdfs好友world...依次類推。那麼hadoop和world有共同的好友hello，所以hadoop和world可能具有好友關係，world就是hadoop的推薦好友。計算出qq檔案內符合上述條件的推薦好友！

實現思路：

在Mapper中，先把qq檔案每行好友，互相轉換（互為好友），結果如下：

hadoop hello
hello hadoop
hdfs world
world hdfs
tom cat
cat tom
cat dog
dog cat
hello world
world hello
hello hdfs
hdfs hello
 

洗牌結果：
hadoop hello

hello hadoop
hello world
hello hdfs

hdfs world
hdfs hello

tom cat

cat tom
cat dog

dog cat

下面是相關程式碼

Mapper程式碼，QqMapper.java

package com.all58.qq;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class QqMapper extends Mapper<LongWritable, Text, Text, Text> {
	
	/*
	 *  Mapping結果：
	 *  hadoop hello
	 *  hello hadoop
		hdfs world
		world hdfs
		tom cat
		cat tom
		cat dog
		dog cat
		hello world
		world hello
		hello hdfs
		hdfs hello
	 */
	@Override
	protected void map(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
		String line = value.toString();
		String[] sp = line.split("\\s+");
		context.write(new Text(sp[0]), new Text(sp[1]));
		context.write(new Text(sp[1]), new Text(sp[0]));
	}
}
 

package com.all58.qq;

import java.io.IOException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;


public class QqReducer extends Reducer<Text, Text, Text, Text> {
	
	/*
		洗牌結果：
		hadoop hello
		
		hello hadoop
		hello world
		hello hdfs
		
		hdfs world
		hdfs hello
		
		tom cat
		
		cat tom
		cat dog
		
		dog cat
	 */
	@Override
	protected void reduce(Text key, Iterable<Text> iter, Context context)
			throws IOException, InterruptedException {
		Set<String> set = new HashSet<>();
		for (Text text : iter) {
			set.add(text.toString());
		}
		if (set.size() > 1) {
			for (Iterator i = set.iterator(); i.hasNext();) {
				String name = (String) i.next();
				for (Iterator j = set.iterator(); j.hasNext();) {
					String other = (String) j.next();
					if (!name.equals(other)) {
						context.write(new Text(name), new Text(other));
					}
				}
			}
		}
	}
}
 

tom	dog
dog	tom
hello	world
world	hello
hdfs	world
hdfs	hadoop
world	hdfs
world	hadoop
hadoop	hdfs
hadoop	world
hello	hdfs
hdfs	hello