uk.ac.starlink.ttools.plot2.data

Class ColumnStorage

java.lang.Object

uk.ac.starlink.ttools.plot2.data.ColumnStorage

public abstract class ColumnStorage
extends Object

Arranges for storage of column data (arrays of typed values) in byte buffers. Any ByteStore type can be used, but there are special entry points for use with storage in named files, which makes it possible to use this class for column storage that persists beyond the length of a JVM.

Since:

6 Jan 2020

Author:

Mark Taylor

Constructor Summary

Constructors

Constructor and Description
ColumnStorage()

Method Summary

Modifier and Type	Method and Description
abstract CachedColumn	createColumn(java.util.function.Supplier<ByteStore> byteStoreSupplier) Creates a CachedColumn for read/write of a data array given any ByteStore type.
abstract CachedColumn	createDiskColumn(File[] files) Returns a CachedColumn that can be used to read/write data using disk storage.
abstract CachedReader	createDiskReader(File[] files) Returns a CachedReader that can be used to read data previously written by this storage object.
abstract long	getDiskRowCount(File[] files) Returns an estimate of the number of rows contained in files previously written by this storage object.
abstract File[]	getFileNames(File baseFile) Returns an array of filenames that can be used for disk-based I/O of data using this storage type.
static ColumnStorage	getStorage(StorageType type) Returns a ColumnStorage object suitable for use with a given StorageType.

Methods inherited from class java.lang.Object

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

Constructor Detail

ColumnStorage

public ColumnStorage()

Method Detail

createColumn

public abstract CachedColumn createColumn(java.util.function.Supplier<ByteStore> byteStoreSupplier)

Creates a CachedColumn for read/write of a data array given any ByteStore type.

Parameters:

byteStoreSupplier - factory for byte storage instances

Returns:

column storage object for data compatible with this

getFileNames

public abstract File[] getFileNames(File baseFile)

Returns an array of filenames that can be used for disk-based I/O of data using this storage type. A base filename is supplied: for a given instance of this class, the returned array will always have the same content for the same base file. This value should be a suitable name for a regular file. The current implementation adds extensions such as ".dat" before using this name.

Parameters:

baseFile - context filename

Returns:

array of one or more filenames that can be used for storage

createDiskColumn

public abstract CachedColumn createDiskColumn(File[] files)
                                       throws IOException

Returns a CachedColumn that can be used to read/write data using disk storage. The files array should be a value returned from getFileNames method.

Parameters:

files - array of filenames into which bytes will be written

Returns:

CachedColumn instance for compatible data write/read

Throws:

IOException

createDiskReader

public abstract CachedReader createDiskReader(File[] files)
                                       throws IOException

Returns a CachedReader that can be used to read data previously written by this storage object. If data has been written to the result of the createDiskColumn method invoked with the same files argument, the reader returned by this method will be able to retrieve it.

Parameters:

files - array of filenames from which bytes will be read

Returns:

CachedReader instance from which compatible data can be read

Throws:

IOException

getDiskRowCount

public abstract long getDiskRowCount(File[] files)

Returns an estimate of the number of rows contained in files previously written by this storage object. The files array should be a value returned from getFileNames method. An approximate value is permitted; if no information is available, -1 may be returned.

Parameters:

files - array of filenames from which bytes will be read

Returns:

best estimate of row count, or -1 if not known

getStorage

public static ColumnStorage getStorage(StorageType type)

Returns a ColumnStorage object suitable for use with a given StorageType. Return values are thread safe.

Parameters:

type - storage type

Returns:

column storage object