Class PositionedStoreStream
- java.lang.Object
-
- java.io.InputStream
-
- org.apache.derby.impl.jdbc.PositionedStoreStream
-
- All Implemented Interfaces:
java.io.Closeable
,java.lang.AutoCloseable
,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:- Access to store must be single threaded.
- This class is not thread safe, and calling the various methods from different threads concurrently can result in inconsistent position values. To avoid redundant internal synchronization, this class assumes and requires external synchronization (also called client-side locking).
-
-
Constructor Summary
Constructors Constructor Description PositionedStoreStream(java.io.InputStream in)
Creates a positioned store stream on top of the specified resettable stream.
-
Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description java.io.InputStream
asInputStream()
Returns a reference to self as anInputStream
.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.
-
-
-
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
- aResetable
-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 classjava.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 classjava.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 classjava.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 classjava.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 interfaceResetable
- 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 interfaceResetable
- 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 interfaceResetable
- 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 interfacePositionedStream
- Parameters:
requestedPos
- requested byte position, first position is0
- Throws:
java.io.EOFException
- if the stream is exhausted before the requested position is reachedjava.io.IOException
- if reading from the store stream failsStandardException
- 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 interfacePositionedStream
- 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 anInputStream
.This method is not allowed to return
null
.- Specified by:
asInputStream
in interfacePositionedStream
- Returns:
- An
InputStream
reference to self.
-
-