hadoop SequenceFile 写入例程注释

import java.io.IOException;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;

// vv SequenceFileWriteDemo
public class SequenceFileWriteDemo {
 
  private static final String[] DATA = {
    "One, two, buckle my shoe",
    "Three, four, shut the door",
    "Five, six, pick up sticks",
    "Seven, eight, lay them straight",
    "Nine, ten, a big fat hen"
  };
 
  public static void main(String[] args) throws IOException {
    String uri = args[0];
    Configuration conf = new Configuration();
    FileSystem fs = FileSystem.get(URI.create(uri), conf);
    Path path = new Path(uri);

    IntWritable key = new IntWritable();
    Text value = new Text();
    SequenceFile.Writer writer = null;
    try {
      writer = SequenceFile.createWriter(fs, conf, path,
          key.getClass(), value.getClass());//返回一个SequenceFile.Writer实例 需要数据流和path对象 将数据写入了path对象
     
      for (int i = 0; i < 100; i++) {
        key.set(100 - i);
        value.set(DATA[i % DATA.length]);
        System.out.printf("[%s]\t%s\t%s\n", writer.getLength(), key, value);//getLength（）方法获取的是当前文件的读取位置
                                                                            //在这个位置开始写
        writer.append(key, value);//将每条记录追加到SequenceFile.Writer实例的末尾
      }
    } finally {
      IOUtils.closeStream(writer);
    }
  }
}