import java.io.InputStream;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;

/** * @author feixu */public class FileSystemCat { /**    * main    * @param args    * @throws Exception  */   public static void main(String[] args) throws Exception {     String uri = args[0];        Configuration conf = new Configuration();        FileSystem fs = FileSystem.get(URI.create(uri), conf);       InputStream in = null;       try {     in = fs.open(new Path(uri));     IOUtils.copyBytes(in, System.out, 4096, false);       } finally {       IOUtils.closeStream(in);      } }

}

2 自行在本地文件系统生成一个大约100字节的文本文件，写一段程序，读入这个文件，并将其第101-120字节的内容写入HDFS成为一个新文件

import java.net.URI;

import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FSDataOutputStream;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IOUtils;

/** * @author feixu * @see FSDataInputStream * @see FSDataOutputStream */public class WriteToHdfs {   /**    * This method is for reading 101~120 bytes from local file and write to hdfs  * @param args which arg[0] should be local disk uri and arg[1] should be hdfs uri    * @throws Exception  */   public static void main(String[] args) throws Exception{      //hdfs uri        String dst = args[1];

      //get hdfs file system instance       Configuration conf = new Configuration();        FileSystem fs = FileSystem.get(URI.create(dst), conf);       FSDataOutputStream out = null;

     try{          //open hdfs output stream         out = fs.create(new Path(dst));

          //write the data from local disk to hdfs          out.write(readFromLocal(args));

      }finally{         IOUtils.closeStream(out);     } }

  /**    * readFromLocal which read 101~120 bytes from the local disk file     * @param args    * @return    * @throws Exception  */   private static byte[] readFromLocal(String[] args) throws Exception{      //local disk uri      String uri = args[0];

      //get local disk file system instance     Configuration conf = new Configuration();        FileSystem fs = FileSystem.getLocal(conf);       FSDataInputStream in = null;

      try{          //open local disk input stream            in = fs.open(new Path(uri));

          //read 101~120 bytes          byte[] buffer = new byte[1024];          in.read(101, buffer, 0, 20);

          return buffer;            }finally{         IOUtils.closeStream(in);      }         }}

3 反向操作，在HDFS中生成一个大约100字节的文本文件，写一段程序，读入这个文件，并将其第101-120字节的内容写入本地文件系统成为一个新文件

import java.net.URI;

import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FSDataOutputStream;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IOUtils;

/** * @author feixu * @see FSDataInputStream * @see FSDataOutputStream * */public class WriteToLocal { /**    * This method is for reading 101~120 bytes from hdfs file and write to local disk     * @param args which arg[0] should be hdfs uri and arg[1] should be local disk uri    * @throws Exception  */   public static void main(String[] args) throws Exception{      //local disk uri      String dst = args[1];

      //get local file system instance      Configuration conf = new Configuration();        FileSystem fs = FileSystem.getLocal(conf);       FSDataOutputStream out = null;

     try{          //open local file's output stream            out = fs.create(new Path(dst));

          //write the data from hdfs to local disk file         out.write(readFromHdfs(args));

      }finally{         IOUtils.closeStream(out);     } }

  /**    * readFromHdfs which read 101~120 bytes from the hdfs file    * @param args    * @return byte[]     * @throws Exception  */   public static byte[] readFromHdfs(String[] args) throws Exception{        //hdfs uri        String uri = args[0];

      //get hdfs file system instance       Configuration conf = new Configuration();        FileSystem fs = FileSystem.get(URI.create(uri), conf);       FSDataInputStream in = null;

      try{          //open hdfs input stream          in = fs.open(new Path(uri));

          //read 101~120 bytes          byte[] buffer = new byte[1024];          in.read(101, buffer, 0, 20);

          return buffer;  

      }finally{         IOUtils.closeStream(in);      } }

}