org.apache.hadoop.fs-BufferedFSInputStream

---

封装了FSInputStream

---

 package org.apache.hadoop.fs;

 import java.io.BufferedInputStream;
 import java.io.IOException;

 /**
  * A class optimizes reading from FSInputStream by bufferring
  */
 //通过缓存优化FSInputStream读取

 public class BufferedFSInputStream extends BufferedInputStream
 implements Seekable, PositionedReadable {
 //两个接口在前面刚看过了，功能为...
   /**
    * Creates a <code>BufferedFSInputStream</code>
    * with the specified buffer size,
    * and saves its  argument, the input stream
    * <code>in</code>, for later use.  An internal
    * buffer array of length  <code>size</code>
    * is created and stored in <code>buf</code>.
    *
    * @param   in     the underlying input stream.
    * @param   size   the buffer size.
    * @exception IllegalArgumentException if size <= 0.
    */
   public BufferedFSInputStream(FSInputStream in, int size) {
     super(in, size);
   }
 //通过跟踪父类代码知道对接了输入流“管道”，初始化了一个大小为size的buffer
   public long getPos() throws IOException {
     return ((FSInputStream)in).getPos()-(count-pos);
   }
 //返回现在的偏移量
   public long skip(long n) throws IOException {
     if (n <= 0) {
       return 0;
     }

     seek(getPos()+n);
     return n;
   }
 //跳过n长度后得到现偏移量
   public void seek(long pos) throws IOException {
     if( pos<0 ) {
       return;
     }
     // optimize: check if the pos is in the buffer
     long end = ((FSInputStream)in).getPos();
     long start = end - count;
     if( pos>=start && pos<end) {
       this.pos = (int)(pos-start);
       return;
     }

     // invalidate buffer
     this.pos = 0;
     this.count = 0;

     ((FSInputStream)in).seek(pos);
   }
 //实现了Seekable的seek方法
   public boolean seekToNewSource(long targetPos) throws IOException {
     pos = 0;
     count = 0;
     return ((FSInputStream)in).seekToNewSource(targetPos);
   }
 //.....
   public int read(long position, byte[] buffer, int offset, int length) throws IOException {
     return ((FSInputStream)in).read(position, buffer, offset, length) ;
   }

   public void readFully(long position, byte[] buffer, int offset, int length) throws IOException {
     ((FSInputStream)in).readFully(position, buffer, offset, length);
   }

   public void readFully(long position, byte[] buffer) throws IOException {
     ((FSInputStream)in).readFully(position, buffer);
   }
 }

---