org.apache.derby.impl.jdbc
Class PositionedStoreStream

java.lang.Object
  extended by java.io.InputStream
      extended by org.apache.derby.impl.jdbc.PositionedStoreStream
All Implemented Interfaces:
java.io.Closeable, PositionedStream, Resetable

public class PositionedStoreStream
extends java.io.InputStream
implements PositionedStream, Resetable

A wrapper-stream able to reposition the underlying store stream.

Where a user expects the underlying stream to be at a given position, reposition(long) must be called with the expected position first. A use case for this scenario is the LOB objects, where you can request a stream and at the same time (this does not mean concurrently) query the LOB about its length or ask to get a part of the LOB returned. Such multiplexed operations must result in consistent and valid data, and to achieve this the underlying store stream must be able to reposition itself. Synchronization: Access to instances of this class must be externally synchronized on the connection synchronization object. There are two reasons for this:

See Also:
EmbedConnection.getConnectionSynchronization()

Field Summary
private  long pos
          Position of the underlying store stream.
private  java.io.InputStream stream
          Underlying store stream serving bytes.
 
Constructor Summary
PositionedStoreStream(java.io.InputStream in)
          Creates a positioned store stream on top of the specified resettable stream.
 
Method Summary
 java.io.InputStream asInputStream()
          Returns a reference to self as an InputStream.
 void closeStream()
          Closes the resettable stream.
 long getPosition()
          Returns the current position of the underlying store stream.
 void initStream()
          Initialize the resettable stream for use.
 int read()
          Reads a single byte from the underlying stream.
 int read(byte[] b)
          Reads a number of bytes from the underlying stream and stores them in the specified byte array.
 int read(byte[] b, int off, int len)
          Reads a number of bytes from the underlying stream and stores them in the specified byte array at the specified offset.
 void reposition(long requestedPos)
          Repositions the underlying store stream to the requested position.
 void resetStream()
          Resets the resettable stream.
 long skip(long toSkip)
          Skips up to the specified number of bytes from the underlying stream.
 
Methods inherited from class java.io.InputStream
available, close, mark, markSupported, reset
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

stream

private final java.io.InputStream stream
Underlying store stream serving bytes.


pos

private long pos
Position of the underlying store stream. Note that the position is maintained by this class, not the underlying store stream itself. Future improvement: Add this functionality to the underlying store stream itself to avoid another level in the stream stack.

Constructor Detail

PositionedStoreStream

public PositionedStoreStream(java.io.InputStream in)
                      throws java.io.IOException,
                             StandardException
Creates a positioned store stream on top of the specified resettable stream.

Upon creation, the underlying stream is initiated and reset to make sure the states of the streams are in sync with each other.

Parameters:
in - a Resetable-stream
Throws:
java.io.IOException
StandardException
Method Detail

read

public int read(byte[] b)
         throws java.io.IOException
Reads a number of bytes from the underlying stream and stores them in the specified byte array.

Overrides:
read in class java.io.InputStream
Returns:
The actual number of bytes read, or -1 if the end of the stream is reached.
Throws:
java.io.IOException - if an I/O error occurs

read

public int read(byte[] b,
                int off,
                int len)
         throws java.io.IOException
Reads a number of bytes from the underlying stream and stores them in the specified byte array at the specified offset.

Overrides:
read in class java.io.InputStream
Returns:
The actual number of bytes read, or -1 if the end of the stream is reached.
Throws:
java.io.IOException - if an I/O error occurs

read

public int read()
         throws java.io.IOException
Reads a single byte from the underlying stream.

Specified by:
read in class java.io.InputStream
Returns:
The next byte of data, or -1 if the end of the stream is reached.
Throws:
java.io.IOException - if an I/O error occurs

skip

public long skip(long toSkip)
          throws java.io.IOException
Skips up to the specified number of bytes from the underlying stream.

Overrides:
skip in class java.io.InputStream
Returns:
The actual number of bytes skipped.
Throws:
java.io.IOException - if an I/O error occurs

resetStream

public void resetStream()
                 throws java.io.IOException,
                        StandardException
Resets the resettable stream.

Specified by:
resetStream in interface Resetable
Throws:
java.io.IOException
StandardException - if resetting the stream in store fails
See Also:
Resetable.resetStream()

initStream

public void initStream()
                throws StandardException
Initialize the resettable stream for use.

Specified by:
initStream in interface Resetable
Throws:
StandardException - if initializing the store in stream fails
See Also:
Resetable.initStream()

closeStream

public void closeStream()
Closes the resettable stream.

Specified by:
closeStream in interface Resetable
See Also:
Resetable.closeStream()

reposition

public void reposition(long requestedPos)
                throws java.io.IOException,
                       StandardException
Repositions the underlying store stream to the requested position.

Repositioning is required because there can be several uses of the store stream, which changes the position of it. If a class is dependent on the underlying stream not changing its position, it must call reposition with the position it expects before using the stream again.

If the repositioning fails because the stream is exhausted, most likely because of an invalid position specified by the user, the stream is reset to position zero and the EOFException is rethrown.

Specified by:
reposition in interface PositionedStream
Parameters:
requestedPos - requested byte position, first position is 0
Throws:
java.io.EOFException - if the stream is exhausted before the requested position is reached
java.io.IOException - if reading from the store stream fails
StandardException - if resetting the store in stream fails, or some other exception happens in store
See Also:
getPosition()

getPosition

public long getPosition()
Returns the current position of the underlying store stream.

Specified by:
getPosition in interface PositionedStream
Returns:
Current byte position of the store stream.

asInputStream

public java.io.InputStream asInputStream()
Description copied from interface: PositionedStream
Returns a reference to self as an InputStream.

This method is not allowed to return null.

Specified by:
asInputStream in interface PositionedStream
Returns:
An InputStream reference to self.

Built on Thu 2012-03-29 21:53:33+0000, from revision ???

Apache Derby V10.6 Internals - Copyright © 2004,2007 The Apache Software Foundation. All Rights Reserved.