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MapReduceJoin.java
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MapReduceJoin.java
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import java.io.IOException;
import java.util.Vector;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.fs.Path;
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.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
public class MapReduceJoin {
public static final String DELIMITER = "\t";
public static class JoinMapper extends Mapper<LongWritable, Text, Text, Text> {
protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, Text>.Context context) throws IOException, InterruptedException {
String filePath = ((FileSplit)context.getInputSplit()).getPath().toString();
String line = value.toString();
String[] values = line.split(DELIMITER);
if (line == null || line.equals(""))
return;
if (filePath.contains("city")) {
if (values.length < 2)
return;
String id = values[0];
String name = values[1];
context.write(new Text(id), new Text("a#" + name));
}
else if (filePath.contains("stat")) {
if (values.length < 3)
return;
String id = values[0];
String year = values[1];
String num = values[2];
context.write(new Text(id), new Text("b#" + year + DELIMITER + num));
}
}
}
public static class JoinReducer extends Reducer<Text,Text,Text,Text> {
protected void reduce(Text key, Iterable<Text> values, Reducer<Text, Text, Text, Text>.Context context) throws IOException, InterruptedException {
Vector<String> vecA = new Vector<String>();
Vector<String> vecB = new Vector<String>();
for (Text val : values) {
String value = val.toString();
if (value.startsWith("a#")) {
vecA.add(value.substring(2));
}
else if (value.startsWith("b#")) {
vecB.add(value.substring(2));
}
}
for (String u : vecA) {
for (String w : vecB) {
context.write(key, new Text(u + DELIMITER + w));
}
}
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "Join");
job.setJarByClass(MapReduceJoin.class);
job.setMapperClass(JoinMapper.class);
job.setReducerClass(JoinReducer.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(Text.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}