無論是在微信還是QQ，我們經常看到好友推薦這樣的功能，其實這個功能是在大資料的基礎上實現的，下面來看具體的程式碼實現：

在src下新增三個類：JobRun.java:

package com.lftgb.mr;

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 JobRun {
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		conf.set("mapred.job.tracker", "192.168.152.128:9001");
		conf.set("fs.default.name", "hdfs://192.168.152.128:9000");
		conf.set("mapred.jar", "C:\\Users\\志鵬\\Desktop\\hadoop程式\\qq.jar");

		try {
			Job job = new Job(conf);
			/*
			 * job.setJarByClass(JobRun.class);
			 * job.setMapperClass(WcMapper.class);
			 * job.setReducerClass(WcReducer.class);
			 * job.setMapOutputKeyClass(Text.class);
			 * job.setMapOutputValueClass(IntWritable.class);
			 * 
			 * // job.setNumReduceTasks(1);//設定reduce任務的個數 預設是一個
			 * 
			 * // mapreduce 輸入資料所在的目錄或者檔案 FileInputFormat.addInputPath(job, new
			 * Path("/usr/my2016")); // mr執行之後的資料資料目錄
			 * FileOutputFormat.setOutputPath(job, new Path("/usr/output"));
			 */

			job.setJobName("qq");
			job.setJarByClass(JobRun.class);
			job.setMapperClass(Test2Mapper.class);
			job.setReducerClass(Test2Reduce.class);
			job.setMapOutputKeyClass(Text.class);
			job.setMapOutputValueClass(IntWritable.class);


			// mapreduce 輸入資料所在的目錄或者檔案
			FileInputFormat.addInputPath(job, new Path("/usr/input/qq/"));
			// mr執行之後的資料資料目錄
			FileOutputFormat.setOutputPath(job, new Path("/usr/output/qq"));
			try {
				System.exit(job.waitForCompletion(true) ? 0 : 1);
			} catch (ClassNotFoundException e) {
				e.printStackTrace();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}
 

package com.lftgb.mr;

import java.io.IOException;

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

public class Test2Mapper extends Mapper<LongWritable, Text, Text, Text> {
	protected void map(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
		String line = value.toString();
		String[] ss = line.split("\t");
		context.write(new Text(ss[0]),new Text(ss[1]));
		context.write(new Text(ss[1]),new Text(ss[0]));	
	}
}
 

package com.lftgb.mr;

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

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

public class Test2Reduce extends Reducer<Text, Text, Text, Text> {
	
	protected void reduce(Text key, Iterable<Text> i,
			Context arg2) throws IOException,
			InterruptedException {
		Set<String>	set= new HashSet<String>();
		for(Text t:i){
			set.add(t.toString());
		}
		if(set.size()>1){
			for (Iterator j = set.iterator(); j.hasNext();) {
				String name = (String) j.next();
				for (Iterator k = set.iterator(); k.hasNext();) {
					String other = (String) k.next();
					if(name.equals(other)){
						arg2.write(new Text(name),new Text(other));
					}
				}
			}
		}
	}
}