环境：

Linux下Eclipse版本

最大值算法代码：

package yunSave;

import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.IntWritable;
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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
//求最大值
public class MaxValue extends Configured implements Tool {
public static class MapClass extends Mapper {
private int maxNum = 0;
public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String[] str = value.toString().split(" ");
try {// 对于非数字字符我们忽略掉
for(int i=0;iint temp = Integer.parseInt(str[i]);
if (temp > maxNum) {
maxNum = temp;
}
}
} catch (NumberFormatException e) {
}
}
@Override
protected void cleanup(Context context) throws IOException,
InterruptedException {
context.write(new IntWritable(maxNum), new IntWritable(maxNum));
}
}
public static class Reduce extends Reducer {
private int maxNum = 0;
public void reduce(IntWritable key, Iterable values, Context context)
throws IOException, InterruptedException {
for (IntWritable val : values) {
if ( val.get() > maxNum) {
maxNum = val.get();
}
}
}
@Override
protected void cleanup(Context context) throws IOException,
InterruptedException {
context.write(new IntWritable(maxNum), new IntWritable(maxNum));
}
}
public int run(String[] args) throws Exception {
Configuration conf = getConf();
Job job = new Job(conf, "MaxNum");
job.setJarByClass(MaxValue.class);
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setMapperClass(MapClass.class);
job.setCombinerClass(Reduce.class);
job.setReducerClass(Reduce.class);
job.setInputFormatClass(TextInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);
job.setOutputKeyClass(IntWritable.class);
job.setOutputValueClass(IntWritable.class);
System.exit(job.waitForCompletion(true) 0 : 1);
return 0;
}
public static void main(String[] args) throws Exception {
long start = System.nanoTime();
int res = ToolRunner.run(new Configuration(), new MaxValue(), args);
System.out.println(System.nanoTime()-start);
System.exit(res);
}
}

输入的文件内容：

[work@master ~]$ hadoop fs -cat input_20141107/555.txt
Warning: $HADOOP_HOME is deprecated.

1 5 10 9999
[work@master ~]$

[work@master ~]$ hadoop fs -cat input_20141107/666.txt
Warning: $HADOOP_HOME is deprecated.

111 222 333 888
[work@master ~]$

Eclipse的执行画面：

1.Argument参数

program Arguments：

hdfs://master:9000/user/work/input_20141107 hdfs://master:9000/user/work/output_20141107

VM Arguments：

-Xms512m -Xmx1024m -XX:MaxPermSize=256m

点击Run之后产生下面的结果

运行结果：

[work@master ~]$ hadoop fs -cat output_20141107/part-r-00000
Warning: $HADOOP_HOME is deprecated.