1 package org.apache.hadoop.fs; 2 3 import java.io.*; 4 import org.apache.hadoop.fs.*; 5 6 /** Stream that permits positional reading. */ 7 //定位流式读取 8 public interface PositionedReadable { 9 /** 10 * Read upto the specified number of bytes, from a given 11 * position within a file, and return the number of bytes read. This does not 12 * change the current offset of a file, and is thread-safe. 13 */ 14 public int read(long position, byte[] buffer, int offset, int length) 15 throws IOException; 16 //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。 17 //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 18 /** 19 * Read the specified number of bytes, from a given 20 * position within a file. This does not 21 * change the current offset of a file, and is thread-safe. 22 */ 23 public void readFully(long position, byte[] buffer, int offset, int length) 24 throws IOException; 25 /** 26 * 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。 27 * 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。 28 */ 29 /** 30 * Read number of bytes equalt to the length of the buffer, from a given 31 * position within a file. This does not 32 * change the current offset of a file, and is thread-safe. 33 */ 34 public void readFully(long position, byte[] buffer) throws IOException; 35 /** 36 * 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 37 * 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。 38 */ 39 40 }