（一）单表关联--mapreduce关联性操作

package mr;

import java.io.IOException;
import java.net.URI;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

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.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;   

public class MyGL {
    private static class MyGLMapper  extends  Mapper<LongWritable, Text, Text, Text>{  
        /*输入类型是LongWritable，Text（上下文）；
                               输出类型是Text，Text（也就是Reduce的输入类型）*/
         public void map(LongWritable k1, Text v1, Context context)   
                             throws java.io.IOException, java.lang.InterruptedException
                                 //map()函数是固定模式的，三个参数
         {
             // 1 2
            String[]  lines= v1.toString().split("\t");  
                                              // \t 在同一个缓冲区内横向跳8个空格（Tab键）;split()方法用于把一个字符串分割
                                              //成字符串数组；v1指的是一行，把第一行的两个单词存进lines
            if(lines.length!=2 || lines[0].trim().equals("child"))      
                return;    //child parent
        
            String word1=lines[0].trim();   //tom       ->去掉 lines[0]里面的空格符
            String word2=lines[1].trim();   //lucy  
            
            context.write(new Text(word1), new Text("1"+","+word1+","+word2));
                                          //第一个Text对应Mapper的第三个Text；第二个Text对应Mapper的第四个Text
            context.write(new Text(word2), new Text("2"+","+word1+","+word2));
            
            //tom,1+tom+lucy
             System.out.println("map......"+word1+"-"+word2);
         }
        
    }
    
    private static class  MyGLReduce extends Reducer<Text, Text, Text, Text>{
         public void reduce(Text key, Iterable<Text> values, Context context) 
                                       throws java.io.IOException, java.lang.InterruptedException
                                  //context：上下文对象，在整个wordcount运算生命周期内存活
         {
              List<String> grandch=new ArrayList();   //泛型
              List<String> grandpa=new ArrayList();
             
                                        /*  lucy 2+tom+lucy
             lucy 1+lucy+mary
             
             2->split[1]    tom     2的话取1
             1->split[2]    mary    1的话取2
             
             k3=tom  v3=mary   把这两个放在上下文
             */

             Iterator<Text>  it=values.iterator();  
                                                // Iterator<Text>--输进来的第二个值
             while(it.hasNext()){ 
                String lines= it.next().toString();      
                                                                         //2，tom，lucy（对应MyGLMapper的context.write()）
                String [] words=lines.split(",");    
                                                                          //劈开 string 数组 ["2","tom","lucy"]
                if(words[0].equals("1")){
                    grandpa.add(words[2]);
                }else if(words[0].equals("2")){
                    grandch.add(words[1]);
                }
                else
                    return;
                
             }
              for(String ch:grandch)
             for(String pa:grandpa)  
             context.write(new Text(ch), new Text(pa));    
             
             System.out.println("reduce......");
         }
         protected void cleanup(Context context) 
                                      throws java.io.IOException, java.lang.InterruptedException{
             
         }
            
    }

    private static String INPUT_PATH="hdfs://master:9000/input/gl.dat";
    private static String OUTPUT_PATH="hdfs://master:9000/output/c/";

    public static void main(String[] args) throws Exception {   
        
        Configuration  conf=new Configuration();
        FileSystem  fs=FileSystem.get(new URI(OUTPUT_PATH),conf);
     
        if(fs.exists(new Path(OUTPUT_PATH)))
                fs.delete(new Path(OUTPUT_PATH));
        
        Job  job=new Job(conf,"myjob");
        
        job.setJarByClass(MyGL.class);
        job.setMapperClass(MyGLMapper.class);
        job.setReducerClass(MyGLReduce.class);
        
         
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        //job.setCombinerClass(MyReduce.class);
         
        
        FileInputFormat.addInputPath(job,new Path(INPUT_PATH));
        FileOutputFormat.setOutputPath(job, new Path(OUTPUT_PATH));
        
        job.waitForCompletion(true);

    }

}

当line[0]=1,line[1]=child;
当line[0]=2,line[2]=grandpa;
测试数据：

child   parent 
Tom Lucy
Tom Jack
Jone    Lucy
Jone    Jack
Lucy    Mary
Lucy    Ben
Jack    Alice
Jack    Jesse
Terry   Alice
Terry   Jesse
Philip  Terry
Philip  Alma
Mark    Terry
Mark    Alma