写一个Hadoop的Java程序可以将txt文本的第一列和第四列提取并排序

以下是一个简单的Java程序，可以读取一个txt文件，提取第一列和第四列，然后按照第一列进行排序。该程序需要在Hadoop环境下运行。

import java.io.IOException;
import java.util.StringTokenizer;
import java.util.TreeMap;
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 SortColumns {

  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()) {
        String[] columns = itr.nextToken().split("\t");
        if (columns.length >= 4) {
          word.set(columns[0]);
          context.write(word, new IntWritable(Integer.parseInt(columns[3])));
        }
      }
    }
  }

  public static class IntSumReducer extends Reducer<Text,IntWritable,Text,IntWritable> {
    private TreeMap<String, Integer> sortedMap = new TreeMap<String, Integer>();

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

    protected void cleanup(Context context) throws IOException, InterruptedException {
      for (String key : sortedMap.keySet()) {
        context.write(new Text(key), new IntWritable(sortedMap.get(key)));
      }
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "sort columns");
    job.setJarByClass(SortColumns.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);
  }
}

在该程序中，首先定义了一个Mapper类来提取第一列和第四列，并将第一列作为键，第四列作为值输出。接着定义了一个Reducer类来对相同键的值进行求和，并使用TreeMap对键进行排序。最后在main方法中配置作业，包括输入和输出路径以及Mapper和Reducer类，然后提交作业并等待完成。