org.apache.hadoop.fs-PositionedReadable

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 package org.apache.hadoop.fs;

 import java.io.*;
 import org.apache.hadoop.fs.*;

 /** Stream that permits positional reading. */
 //定位流式读取
 public interface PositionedReadable {
   /**
    * Read upto the specified number of bytes, from a given
    * position within a file, and return the number of bytes read. This does not
    * change the current offset of a file, and is thread-safe.
    */
   public int read(long position, byte[] buffer, int offset, int length)
     throws IOException;
   //读取文件流中最多到length大小的字节，到字节缓冲区buffer中,它是从给定的position位置开始读取的。
   //该读取方式不改变文件的当前偏移位置offset，并且该方法是线程安全的
   /**
    * Read the specified number of bytes, from a given
    * position within a file. This does not
    * change the current offset of a file, and is thread-safe.
    */
   public void readFully(long position, byte[] buffer, int offset, int length)
     throws IOException;
   /**
    * 读取文件流中length大小的字节，到字节缓冲区buffer中,它是从给定的position位置开始读取的。
    * 该读取方式不改变文件的当前偏移位置offset，并且该方法是线程安全的。
    */
   /**
    * Read number of bytes equalt to the length of the buffer, from a given
    * position within a file. This does not
    * change the current offset of a file, and is thread-safe.
    */
   public void readFully(long position, byte[] buffer) throws IOException;
   /**
    * 读取文件流中buffer长度的字节，到字节缓冲区buffer中,它是从给定的position位置开始读取的
    * 该读取方式不改变文件的当前偏移位置offset，并且该方法是线程安全的。
    */  

 }

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