环境：

Linux系统centOS6.3(64bit)

hadoop1.1.2

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<LongWritable, Text, IntWritable, IntWritable> {  
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;i<str.length;i++){
int 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<IntWritable, IntWritable, IntWritable, IntWritable> {  
private int maxNum = 0;  
public void reduce(IntWritable key, Iterable<IntWritable> 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.


9999 9999
[work@master ~]$ 

Hadoop最大值整数算法详解