uk.ac.starlink.feather

Class AbstractItemAccumulator

java.lang.Object

uk.ac.starlink.feather.AbstractItemAccumulator

All Implemented Interfaces:

ItemAccumulator

public abstract class AbstractItemAccumulator
extends Object
implements ItemAccumulator

Partial ItemAccumulator implementation that handles generic aspects including writing the optional validity mask.

Since:

27 Feb 2020

Author:

Mark Taylor

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AbstractItemAccumulator(StoragePolicy storage, boolean isNullable) Constructor.

Method Summary

Modifier and Type	Method and Description
protected abstract void	addDataItem(Object item) Adds the given item to the list to be output.
void	addItem(Object item) Receive the next value in the column.
void	close() Tidies up resources, in particular discarding any off-heap temporary storage that may have been allocated.
protected abstract void	closeData() Releases resources.
protected boolean	isNull(Object item) Tests whether a given added data item is null (whether it needs to be flagged as null in the validity mask).
uk.ac.bristol.star.feather.ColStat	writeColumnBytes(OutputStream out) Writes a feather-format column to the given output stream representing all the objects submitted by prior valls to the addItem method.
abstract long	writeDataBytes(OutputStream out) Writes the bytes constituting the data stream for this column, excluding any optional validity mask.

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractItemAccumulator

protected AbstractItemAccumulator(StoragePolicy storage,
                                  boolean isNullable)

Constructor.

Parameters:

storage - storage policy for buffering output data

isNullable - if true, preparations will be made to write the validity mask; it will only be actually output if there are some null values

Method Detail

addDataItem

protected abstract void addDataItem(Object item)
                             throws IOException

Adds the given item to the list to be output. This method is invoked from this AbstractItemAccumulator's addItem(java.lang.Object) method, and is just the hook for the subclass-specific behaviour.

Parameters:

item - cell value

Throws:

IOException

closeData

protected abstract void closeData()
                           throws IOException

Releases resources. This method is invoked from this AbstractItemAccumulator's close() method, and is just the hook for the subclass-specific behaviour.

Throws:

IOException

isNull

protected boolean isNull(Object item)

Tests whether a given added data item is null (whether it needs to be flagged as null in the validity mask). This method is only ever called for nullable columns (if the isNullable flag was set true at construction time).

The default implementation tests whether the supplied item is in fact null, but it may be overridden.

Parameters:

item - value to test

Returns:

true iff item is to be flagged null

writeDataBytes

public abstract long writeDataBytes(OutputStream out)
                             throws IOException

Writes the bytes constituting the data stream for this column, excluding any optional validity mask. Note the output does not need to be aligned on an 8-byte boundary.

Parameters:

out - destination stream

Returns:

number of bytes written

Throws:

IOException

close

public void close()
           throws IOException

Description copied from interface: ItemAccumulator

Tidies up resources, in particular discarding any off-heap temporary storage that may have been allocated. Calling any of the other methods of this interface after closing it has undefined effects. Multiple calls to close are permitted.

Specified by:

close in interface ItemAccumulator

Throws:

IOException

addItem

public void addItem(Object item)
             throws IOException

Description copied from interface: ItemAccumulator

Receive the next value in the column.

Specified by:

addItem in interface ItemAccumulator

Parameters:

item - column cell value

Throws:

IOException

writeColumnBytes

public uk.ac.bristol.star.feather.ColStat writeColumnBytes(OutputStream out)
                                                    throws IOException

Description copied from interface: ItemAccumulator

Writes a feather-format column to the given output stream representing all the objects submitted by prior valls to the addItem method. The number of bytes written must be a multiple of 8.

Specified by:

writeColumnBytes in interface ItemAccumulator

Parameters:

out - destination stream

Returns:

details about what was written

Throws:

IOException