java统计hdfs上多个文件行数

您可以使用Hadoop的MapReduce框架来统计HDFS上多个文件的行数。以下是一个示例Java代码，它使用MapReduce框架来计算多个文件的总行数：

import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
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 LineCounter {
  
  public static class LineCounterMapper
       extends Mapper<LongWritable, Text, Text, IntWritable>{
    
    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();
      
    public void map(LongWritable key, Text value, Context context
                    ) throws IOException, InterruptedException {
      word.set("lines");
      context.write(word, one);
    }
  }
  
  public static class LineCounterReducer
       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, "line count");
    job.setJarByClass(LineCounter.class);
    job.setMapperClass(LineCounterMapper.class);
    job.setCombinerClass(LineCounterReducer.class);
    job.setReducerClass(LineCounterReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    for (int i = 0; i < args.length - 1; ++i) {
      FileInputFormat.addInputPath(job, new Path(args[i]));
    }
    FileOutputFormat.setOutputPath(job,
      new Path(args[args.length - 1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

您可以在命令行中使用以下命令来运行此代码：

hadoop jar linecounter.jar input1 input2 input3 output

其中，`input1`、`input2`和`input3`是要计算行数的文件，`output`是输出目录。运行后，输出目录中将包含一个名为`part-r-00000`的文件，其中包含所有文件的总行数。