程序准备

以下代码来源于Hadoop官网Wrodcount实例代码

import java.io.IOException;
import java.util.StringTokenizer;

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.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.output.FileOutputFormat;

public class WordCount {

  public static class TokenizerMapper
       extends Mapper<Object, Text, Text, IntWritable>{

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    public void map(Object key, Text value, Context context
                    ) throws IOException, InterruptedException {
      StringTokenizer itr = new StringTokenizer(value.toString());
      while (itr.hasMoreTokens()) {
        word.set(itr.nextToken());
        context.write(word, one);
      }
    }
  }

  public static class IntSumReducer
       extends Reducer<Text,IntWritable,Text,IntWritable> {
    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<IntWritable> values,
                       Context context
                       ) throws IOException, InterruptedException {
      int sum = 0;
      for (IntWritable val : values) {
        sum += val.get();
      }
      result.set(sum);
      context.write(key, result);
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "word count");
    job.setJarByClass(WordCount.class);
    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumReducer.class);
    job.setReducerClass(IntSumReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

设置JDK和Hadoop环境变量，假设java安装路径为/usr/java/jdk1.7.0_51
export JAVA_HOME=/usr/java/jdk1.7.0_51
export PATH=${JAVA_HOME}/bin:${PATH}
export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar
编译程序
mkdir wordcount_classes
Hadoop com.sun.tools.javac.Main -d wordcount_classes/ WordCount.java
jar cvf wordcount.jar -C wordcount_classes .
这样就得到了wordcount.jar