测试数据:
file1.txt
102
10
39
109
200
11
2
90
28
file2.txt
5
2
30
838
10005
mapper代码:
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
public class MaxMinMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
private static final Text KEY = new Text("key");
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
context.write(KEY, new IntWritable(Integer.valueOf(value.toString().trim())));
}
}
reducer代码:
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import java.io.IOException;
public class MaxMinReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
@Override
protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
long min = Long.MAX_VALUE;
long max = Long.MIN_VALUE;
for(IntWritable val : values) {
if (min > val.get()) {
min = val.get();
}
if (max < val.get()) {
max = val.get();
}
}
context.write(new Text("MIN:"), new IntWritable(Integer.valueOf("" + min)));
context.write(new Text("MAX:"), new IntWritable(Integer.valueOf("" + max)));
}
}
main代码:
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.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import java.io.IOException;
/**
* 求最大最小值。数据量不多的情况下,直接把输入数据做为一个相同key和list<value>形式
*/
public class JobMain {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
if(args.length != 2) {
System.err.println("Usage: MinMaxTemperature<input path> <output path>");
System.exit(-1);
}
Configuration conf = new Configuration();
Job job = Job.getInstance(conf, "max_min_job");
job.setJarByClass(Job.class);
job.setMapperClass(MaxMinMapper.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);
job.setReducerClass(MaxMinReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(args[0]));
Path outDirPath = new Path(args[1]);
FileSystem fs = FileSystem.get(conf);
if(fs.exists(outDirPath)) {
fs.delete(outDirPath, true);
}
FileOutputFormat.setOutputPath(job, outDirPath);
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
结果:
MIN: 2
MAX: 10005