案例:获取孙子和祖父母的列表
【单表关联.txt】
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
思路分析:
Tom Lucy/Jack
Lucy Mary/Ben
Jack Alice/Jesse
Jone Lucy/Jack
Lucy Mary/Ben
Jack Alice/Jesse
1 2
左表 右表
k-------------v (孩子与父母) k-------------v(父母与祖父母)
parent child child parent
grandchild grandparent
mapper:
确定标识符,左右表
<k2,v2>--> <parent,"1"+child>
reducer:
遍历value,做笛卡尔积
<k3,v3>--> <grandchild,grandparent>
代码如下:
Mapper端:
package com.hyxy.hadoop.join.single;
import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
public class SingleJoinMapper extends Mapper<LongWritable, Text, Text, Text>{
@Override
protected void map(LongWritable key, Text value,Context context)throws IOException, InterruptedException {
/*
* 置空表头
*/
String line = value.toString();
if(line.contains("child")||line.contains("parent")){
return ;
}
/*
* 确定左右表和表关系标识
*/
//空格切分文件内容
StringTokenizer st = new StringTokenizer(value.toString());
String child = st.nextToken();//返回孩子字段
String parent = st.nextToken();//返回父母字段
//判断左表和右表的child
if(child.compareTo("child")!=0){
//标识1:孩子与父母关系
context.write(new Text(parent), new Text("1"+"+"+child));
//标识2:父母与祖父母
context.write(new Text(child), new Text("2"+"+"+parent));
}
}
}
Reducer端:
package com.hyxy.hadoop.join.single;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
/*
* <>
*/
public class SingleJoinReducer extends Reducer<Text, Text, Text, Text>{
List<String> grandchild = new ArrayList<String>();
List<String> grandparent = new ArrayList<String>();
private Text _key = new Text();
private Text _value = new Text();
@Override
//只调用一次,做表头
protected void setup(org.apache.hadoop.mapreduce.Reducer.Context context)throws IOException, InterruptedException {
context.write("grandchild", "grandparent");
}
@Override
protected void reduce(Text key, Iterable<Text> values,Context context)throws IOException, InterruptedException {
//遍历value,讲元素添加到集合中
for (Text value : values) {
//获取行内容
String line = value.toString();
//判断字符串是否以指定的前缀开始,判断是否是左表
if(line.startsWith("1")){
//将截取到的内容添加到grandchild集合中
grandchild.add(line.substring(2));
}else{
//将截取到的内容添加到grandparent集合中
grandparent.add(line.substring(2));
}
}
//笛卡尔积,遍历grandchild集合
for (String child: grandchild) {
//遍历grandparent集合
for(String parent: grandparent){
//将遍历出的元素赋值给_key和_value
_key.set(child);
_value.set(parent);
context.write(_key,_value);
}
}
//清空集合
grandchild.clear();
grandparent.clear();
}
}
Driver端:
package com.hyxy.hadoop.join.single;
import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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;
import com.hyxy.hadoop.join.multi.MultiJoinDriver;
import com.hyxy.hadoop.join.multi.MultiJoinMapper;
import com.hyxy.hadoop.join.multi.MultiJoinReducer;
public class SingleJoinDriver {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
Configuration conf = new Configuration();
Path outfile = new Path("file:///G:/SingleOut");
FileSystem fs = outfile.getFileSystem(conf);
if(fs.exists(outfile)){
fs.delete(outfile,true);
}
Job job = Job.getInstance(conf);
job.setJarByClass(SingleJoinDriver.class);
job.setJobName("Single Demo");
job.setMapperClass(SingleJoinMapper.class);
job.setReducerClass(SingleJoinReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
FileInputFormat.addInputPath(job, new Path("file:///G:/测试数据/单表关联/"));
FileOutputFormat.setOutputPath(job, outfile);
System.exit(job.waitForCompletion(true)?0:1);
}
}
输出结果样式:
grandchild grandparent
Tom Alice
Tom Jesse
Jone Alice
Jone Jesse
Tom Ben
Tom Mary
Jone Ben
Jone Mary
Philip Alice
Philip Jesse
Mark Alice
Mark Jesse