摘要：
importjava.util.ArrayList；importorg.apach.hadoop.io.Text；importorg.apach.hadoop.mapreduce.Mapper；查找孙子孙女表*/publicclassSingleTableRelation｛publicstaticintime=0；
1. 实例描述
单表关联这个实例要求从给出的数据中寻找出所关心的数据，它是对原始数据所包含信息的挖掘。
实例中给出child-parent 表， 求出grandchild-grandparent表。
输入数据 file01:
child parent
Tom Lucy
Tom Jack
Jone Lucy
Jone Jack
Lucy Marry
Lucy Ben
Jack Alice
Jack Jesse
Terry Alice
Terry Jesse
Philip Terry
Philip Alma
Mark Terry
Mark Alma希望输出为:
grandchild grandparent
Tom Alice
Tom Jesse
Jone Alice
Jone Jesse
Tom Marry
Tom Ben
Jone Marry
Jone Ben
Philip Alice
Philip Jesse
Mark Alice
Mark Jesse2. 设计思路
1. 在map阶段，将原数据进行分割，将parent作为map输出的key值，child作为map输出的value值，这样形成左表。
2. 同时在map阶段过程中，将child作为map输出的key值，parent作为map输出的value值，这样形成右表。
3. 连接左表的paren列和右表的child列。
3. 具体实现
package tablerelation; import java.io.IOException; import java.util.ArrayList; import java.util.List; import java.util.StringTokenizer; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.Path; 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; /** * * @author Amei 单表链接，求grandchild grandparent表 */ public class SingleTableRelation { public static int time = 0; /** * * @author Amei 左表的paren 和 右表的 child 做链接 */ public static class Map extends Mapper<LongWritable, Text, Text, Text> { protected void map(LongWritable key, Text value, Context context) throws java.io.IOException, InterruptedException {
// 左右表的标识 int relation; StringTokenizer tokenizer = new StringTokenizer(value.toString()); String child = tokenizer.nextToken(); String parent = tokenizer.nextToken(); if (child.compareTo("child") != 0) { // 左表 relation = 1; context.write(new Text(parent), new Text(relation + "+" + child)); // 右表 relation = 2; context.write(new Text(child), new Text(relation + "+" + parent)); } }; } public static class Reduce extends Reducer<Text, Text, Text, Text> { protected void reduce(Text key, Iterable<Text> values, Reducer<Text, Text, Text, Text>.Context output) throws java.io.IOException, InterruptedException { int grandchildnum = 0; int grandparentnum = 0; List<String> grandchilds = new ArrayList<>(); List<String> grandparents = new ArrayList<>(); /** 输出表头 */ if (time == 0) { output.write(new Text("grandchild"), new Text("grandparent")); time++; } for (Text val : values) { String record = val.toString(); char relation = record.charAt(0); // 取出此时key所对应的child if (relation == '1') { String child = record.substring(2); grandchilds.add(child); grandchildnum++; } // 取出此时key所对应的parent else { String parent = record.substring(2); grandparents.add(parent); grandparentnum++; } } if (grandchildnum != 0 && grandparentnum != 0) { for (int i = 0; i < grandchildnum; i++) for (int j = 0; j < grandparentnum; j++) output.write(new Text(grandchilds.get(i)), new Text( grandparents.get(j))); } } } public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException { Configuration conf = new Configuration(); Job job = new Job(conf,"single tale relation"); job.setJarByClass(SingleTableRelation.class); job.setMapperClass(Map.class); job.setReducerClass(Reduce.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(Text.class); FileInputFormat.addInputPath(job, new Path("/user/hadoop_admin/singletalein")); FileOutputFormat.setOutputPath(job, new Path("/user/hadoop_admin/singletableout")); System.exit((job.waitForCompletion(true) ? 0 : 1)); } }