mapreduce编程：单表自连接

程序：

package my.hadoopstudy;  import java.util.*;import java.io.*;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.mapred.TextInputFormat;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;import org.apache.hadoop.mapreduce.lib.input.KeyValueTextInputFormat;public class oneTableConnect {  public static class tableMapper extends Mapper<Text, Text, Text, Text> {  @Override  public void map(Text key, Text value, Context context) throws IOException, InterruptedException  {   context.write(key, new Text( "1" + value.toString()));   context.write(value, new Text("0" + key.toString()));  } }   public static class tableReducer extends Reducer<Text, Text, Text, Text> {  @Override  public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException  {   List<String> gChildren=new ArrayList<String>();   List<String> gParents =new ArrayList<String>();   for(Text val : values)   {    if(val.toString().charAt(0)  == '0')// the key's child.    {       gChildren.add(val.toString().substring(1));    }    else//the key's parent.    {       gParents.add(val.toString().substring(1));    }   }      for(int i=0; i<gChildren.size(); i++)    for(int j=0;j<gParents.size();j++)    {       context.write(new Text(gChildren.get(i)), new Text(gParents.get(j)));    }  }  }  public static void main(String[] args) throws Exception {  Configuration conf = new Configuration();  conf.set("mapreduce.input.keyvaluelinerecordreader.key.value.separator", " ");    Job job = new Job(conf, "tableConnect");  job.setJarByClass(oneTableConnect.class);    job.setMapperClass(tableMapper.class);  job.setReducerClass(tableReducer.class);    job.setOutputKeyClass(Text.class);  job.setOutputValueClass(Text.class);    job.setInputFormatClass(KeyValueTextInputFormat.class);  job.setOutputFormatClass(TextOutputFormat.class);    FileInputFormat.addInputPath(job, new Path(args[0]));  FileOutputFormat.setOutputPath(job, new Path(args[1]));    System.exit( job.waitForCompletion(true) ? 0 : 1); }}

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