uk.ac.starlink.fits

Class BlockInput

java.lang.Object

uk.ac.starlink.fits.BlockInput

All Implemented Interfaces:

BasicInput

Direct Known Subclasses:

BlockMappedInput, MultiByteBufferInput

public abstract class BlockInput
extends Object
implements BasicInput

Partial random-access BasicInput implementation based on a set of ByteBuffers. These may be obtained eagerly or lazily, as defined by the implementation.

Since:

18 Mar 2021

Author:

Mark Taylor

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	BlockInput(int nblock) Constructor.

Method Summary

Modifier and Type	Method and Description
protected abstract ByteBuffer	acquireBlock(int iblock) Obtains a buffer corresponding to a named block of the stream.
void	close() Releases resources belonging to this object.
int	getBlockCount() Returns the number of mapped blocks used.
abstract long	getBlockOffset(int iblock, int offsetInBlock) Returns the offset into this stream corresponding to a given block index and offset into that block.
abstract int[]	getBlockPos(long offset) Returns the block location of a given byte offset.
long	getOffset() Returns the curent position in this stream (optional operation).
boolean	isRandom() Indicates whether this object supports random access.
byte	readByte() Reads a byte from the stream.
void	readBytes(byte[] bbuf) Reads bytes into an array from the stream.
double	readDouble() Reads an 8-byte floating point value from the stream.
float	readFloat() Reads a 4-byte floating point value from the stream.
int	readInt() Reads a 4-byte integer from the stream.
long	readLong() Reads an 8-byte integer from the stream.
short	readShort() Reads a 2-byte integer from the stream.
void	seek(long offset) Moves the current position of this stream to a given byte offset (optional operation).
void	skip(long nbyte) Skips a given number of bytes forwards through the stream.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BlockInput

protected BlockInput(int nblock)

Constructor.

Parameters:

nblock - number of buffers

Method Detail

readByte

public byte readByte()
              throws IOException

Description copied from interface: BasicInput

Reads a byte from the stream. The current position is advanced.

Specified by:

readByte in interface BasicInput

Returns:

byte value

Throws:

IOException

readShort

public short readShort()
                throws IOException

Description copied from interface: BasicInput

Reads a 2-byte integer from the stream. The current position is advanced.

Specified by:

readShort in interface BasicInput

Returns:

short value

Throws:

IOException

readInt

public int readInt()
            throws IOException

Description copied from interface: BasicInput

Reads a 4-byte integer from the stream. The current position is advanced.

Specified by:

readInt in interface BasicInput

Returns:

int value

Throws:

IOException

readLong

public long readLong()
              throws IOException

Description copied from interface: BasicInput

Reads an 8-byte integer from the stream. The current position is advanced.

Specified by:

readLong in interface BasicInput

Returns:

long value

Throws:

IOException

readFloat

public float readFloat()
                throws IOException

Description copied from interface: BasicInput

Reads a 4-byte floating point value from the stream. The current position is advanced.

Specified by:

readFloat in interface BasicInput

Returns:

float value

Throws:

IOException

readDouble

public double readDouble()
                  throws IOException

Description copied from interface: BasicInput

Reads an 8-byte floating point value from the stream. The current position is advanced.

Specified by:

readDouble in interface BasicInput

Returns:

double value

Throws:

IOException

readBytes

public void readBytes(byte[] bbuf)
               throws IOException

Description copied from interface: BasicInput

Reads bytes into an array from the stream. The current position is advanced.

Specified by:

readBytes in interface BasicInput

Parameters:

bbuf - array into which the bytes are read; the number of bytes read is the length of the array

Throws:

IOException

close

public void close()

Description copied from interface: BasicInput

Releases resources belonging to this object. Attempts to use it after a call to this method result in undefined behaviour.

Specified by:

close in interface BasicInput

isRandom

public boolean isRandom()

Description copied from interface: BasicInput

Indicates whether this object supports random access. The seek and getOffset methods may only be called if this method returns true.

Specified by:

isRandom in interface BasicInput

Returns:

true iff random access is supported

getBlockPos

public abstract int[] getBlockPos(long offset)

Returns the block location of a given byte offset.

This does the opposite of getBlockOffset.

Parameters:

offset - offset into this input stream

Returns:

2-element array giving [blockIndex, offsetInBlock]

getBlockOffset

public abstract long getBlockOffset(int iblock,
                                    int offsetInBlock)

Returns the offset into this stream corresponding to a given block index and offset into that block.

This does the opposite of getBlockPos.

Parameters:

iblock - block index

offsetInBlock - offset into that block

Returns:

offset into stream

acquireBlock

protected abstract ByteBuffer acquireBlock(int iblock)
                                    throws IOException

Obtains a buffer corresponding to a named block of the stream. The buffer's position must be zero. This method is called whenever a buffer is required which is not the same as the most recently used one.

Parameters:

iblock - block index

Returns:

byte buffer for given block, positioned at start

Throws:

IOException

seek

public void seek(long offset)
          throws IOException

Description copied from interface: BasicInput

Moves the current position of this stream to a given byte offset (optional operation).

Specified by:

seek in interface BasicInput

Throws:

IOException

getOffset

public long getOffset()

Description copied from interface: BasicInput

Returns the curent position in this stream (optional operation).

Specified by:

getOffset in interface BasicInput

skip

public void skip(long nbyte)
          throws IOException

Description copied from interface: BasicInput

Skips a given number of bytes forwards through the stream. An exception is thrown if there are not enough bytes left.

Specified by:

skip in interface BasicInput

Parameters:

nbyte - number of bytes to skip

Throws:

IOException

getBlockCount

public int getBlockCount()

Returns the number of mapped blocks used.

Returns:

block count