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From John Lilley <john.lil...@redpoint.net>
Subject RE: Two questions about FSDataInputStream
Date Wed, 13 Nov 2013 13:58:51 GMT
Ted,
Thanks, I see it now.  Sorry for the bother... I must be too tired or something ;-)
John


From: Ted Yu [mailto:yuzhihong@gmail.com]
Sent: Tuesday, November 12, 2013 4:15 PM
To: common-user@hadoop.apache.org
Subject: Re: Two questions about FSDataInputStream

For #1, I see the following in output of javap:

  public synchronized void seek(long) throws java.io.IOException;

which is described here:
http://hadoop.apache.org/docs/current/api/org/apache/hadoop/fs/FSDataInputStream.html#seek(long)

On Tue, Nov 12, 2013 at 3:08 PM, John Lilley <john.lilley@redpoint.net<mailto:john.lilley@redpoint.net>>
wrote:
First, this documentation: http://hadoop.apache.org/docs/current/api/org/apache/hadoop/fs/FSDataInputStream.html
claims that FSDataInputStream has a seek() method, but javap doesn't show one:
$ javap -classpath [haddoopjars]  org.apache.hadoop.fs.FSDataInputStream
Compiled from "FSDataInputStream.java"
public class org.apache.hadoop.fs.FSDataInputStream extends java.io.DataInputStream implements
org.apache.hadoop.fs.Seek
able,org.apache.hadoop.fs.PositionedReadable,java.io.Closeable,org.apache.hadoop.fs.ByteBufferReadable,org.apache.hadoop
.fs.HasFileDescriptor,org.apache.hadoop.fs.CanSetDropBehind,org.apache.hadoop.fs.CanSetReadahead
{
  public org.apache.hadoop.fs.FSDataInputStream(java.io.InputStream) throws java.io.IOException;
  public synchronized void seek(long) throws java.io.IOException;
  public long getPos() throws java.io.IOException;
  public int read(long, byte[], int, int) throws java.io.IOException;
  public void readFully(long, byte[], int, int) throws java.io.IOException;
  public void readFully(long, byte[]) throws java.io.IOException;
  public boolean seekToNewSource(long) throws java.io.IOException;
  public java.io.InputStream getWrappedStream();
  public int read(java.nio.ByteBuffer) throws java.io.IOException;
  public java.io.FileDescriptor getFileDescriptor() throws java.io.IOException;
  public void setReadahead(java.lang.Long) throws java.io.IOException, java.lang.UnsupportedOperationException;
  public void setDropBehind(java.lang.Boolean) throws java.io.IOException, java.lang.UnsupportedOperationException;
}

Second, after every call to inputStream.read(position, byteArray, 0, size), the getPos() call
returns the same answer.  Should it change?

Given the lack of all these things, how is one supposed to call read(ByteBuffer) for random
I/O?

john



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