uk.ac.starlink.votable

Class FitsPlusTableBuilder

java.lang.Object

uk.ac.starlink.votable.FitsPlusTableBuilder

All Implemented Interfaces:

MultiTableBuilder, TableBuilder

public class FitsPlusTableBuilder
extends Object
implements TableBuilder, MultiTableBuilder

Table builder which can read files in 'fits-plus' format (as written by FitsPlusTableWriter). This looks for a primary header in the FITS file which contains the VOTMETA header (in fact it is quite inflexible about what it recognises as this format - see isMagic(byte[])) and tries to interpret the data array as a 1-d array of bytes representing the XML of a VOTable document. This VOTable document should have one or more TABLE elements with no DATA content - the table data is got from the extension extension HDUs, one per table, and they must be BINTABLE extensions matching the metadata described by the VOTable.

The point of all this is so that you can store VOTables in the efficient FITS format (it can be mapped if it's on local disk, which makes table creation practically instantaneous, even for random access) without sacrificing any of the metadata that you want to encode in VOTable format.

Since:

27 Aug 2004

Author:

Mark Taylor (Starlink)

See Also:

FitsPlusTableWriter

Constructor Summary

Constructors

Constructor and Description
FitsPlusTableBuilder() Default constructor.
FitsPlusTableBuilder(WideFits wide) Constructor.

Method Summary

Modifier and Type	Method and Description
boolean	canImport(DataFlavor flavor) Returns true for a flavor with the MIME type "application/fits".
String	getFormatName() Returns the name of the format which can be read by this handler.
static boolean	isMagic(byte[] buffer) Tests whether a given buffer contains bytes which might be the first few bytes of a FitsPlus table.
boolean	looksLikeFile(String location) Indicates whether the given location string is of a familiar form for this builder.
StarTable	makeStarTable(DataSource datsrc, boolean wantRandom, StoragePolicy storagePolicy) Constructs a StarTable based on a given DataSource.
TableSequence	makeStarTables(DataSource datsrc, StoragePolicy storagePolicy) Constructs a sequence of StarTables based on a given DataSource.
void	streamStarTable(InputStream in, TableSink sink, String pos) Reads a table from an input stream and writes it a row at a time to a sink.

Methods inherited from class java.lang.Object

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

Constructor Detail

FitsPlusTableBuilder

public FitsPlusTableBuilder()

Default constructor.

FitsPlusTableBuilder

public FitsPlusTableBuilder(WideFits wide)

Constructor.

Parameters:

wide - convention for representing extended columns; use null to avoid use of extended columns

Method Detail

getFormatName

public String getFormatName()

Description copied from interface: TableBuilder

Returns the name of the format which can be read by this handler. Matching against this string may be used by callers to identify or select this handler from a list.

Specified by:

getFormatName in interface TableBuilder

Returns:

one-word description of this handler's format

looksLikeFile

public boolean looksLikeFile(String location)

Description copied from interface: TableBuilder

Indicates whether the given location string is of a familiar form for this builder. Implementations should return true if there is a good chance that a file with the given location can be interpreted by this reader, for instance if it has a suitable file extension.

This method may be used to guess, on a best-efforts basis, whether this builder is suitable for reading a file from a given location. Attempts may still be made to read inputs for which this method returns false. It is less important for builders that can recognise files by magic number, which is generally preferable to using filenames.

Specified by:

looksLikeFile in interface TableBuilder

Parameters:

location - the location string, such as a filename or URL (not null)

Returns:

true iff there is a good chance that the named input can be interpreted by this reader

makeStarTable

public StarTable makeStarTable(DataSource datsrc,
                               boolean wantRandom,
                               StoragePolicy storagePolicy)
                        throws IOException

Description copied from interface: TableBuilder

Constructs a StarTable based on a given DataSource. If the source is not recognised or this builder does not know how to construct a table from it, then a TableFormatException should be thrown. If this builder thinks it should be able to handle the source but an error occurs during processing, an IOException can be thrown.

The wantRandom parameter is used to indicate whether, ideally, a random-access table should be returned. There is no requirement for the builder to honour this request, but if it knows how to make both random and non-random tables, it can use this flag to decide which to return.

Note: the presence of the wantRandom parameter is somewhat misleading. TableBuilder implementations usually should, and do, ignore it (it would be removed from the interface if it were not for backward compatibility issues). Regardless of the value of this parameter, implementations should return a random-access table only if it is easy for them to do so; in particular they should not use the supplied storagePolicy, or any other resource-expensive measure, to randomise a sequential table just because the wantRandom parameter is true.

Specified by:

makeStarTable in interface TableBuilder

Parameters:

datsrc - the DataSource containing the table resource

wantRandom - whether, preferentially, a random access table should be returned

storagePolicy - a StoragePolicy object which may be used to supply scratch storage if the builder needs it

Returns:

a StarTable made out of datsrc

Throws:

TableFormatException - if the table is not of a kind that can be handled by this handler

IOException - if an unexpected I/O error occurs during processing

makeStarTables

public TableSequence makeStarTables(DataSource datsrc,
                                    StoragePolicy storagePolicy)
                             throws IOException

Description copied from interface: MultiTableBuilder

Constructs a sequence of StarTables based on a given DataSource. If the source is not recognised or this object does not know how to make tables from it, then a TableFormatException should be thrown. If this builder thinks it should be able to handle the source but an error occurs during processing, an IOException can be thrown.

If the position of the data source is not null, then this method should return a sequence containing a single table, the one which would be returned by the makeStarTable method with that position.

Specified by:

makeStarTables in interface MultiTableBuilder

Parameters:

datsrc - the DataSource containing the table resource

storagePolicy - a StoragePolicy object which may be used to supply scratch storage if the builder needs it

Returns:

an array of StarTables read from datsrc

Throws:

TableFormatException - if the table is not of a kind that can be handled by this handler

IOException - if an unexpected I/O error occurs during processing

streamStarTable

public void streamStarTable(InputStream in,
                            TableSink sink,
                            String pos)
                     throws IOException

Description copied from interface: TableBuilder

Reads a table from an input stream and writes it a row at a time to a sink. Not all implementations will be able to do this; for instance, extracting the table from the data may be a two-pass process. Implementations which are unable to perform this function should throw a TableFormatException.

The input stream should be prepared for use prior to calling this method, so implementations should not in general attempt to decompress or buffer istrm.

Specified by:

streamStarTable in interface TableBuilder

Parameters:

in - input stream containing table data

sink - destination of the table

pos - position identifier describing the location of the table within the stream; see DataSource.getPosition() (may be null)

Throws:

TableFormatException - if the table can't be streamed or the data is malformed

IOException - if some other error occurs

canImport

public boolean canImport(DataFlavor flavor)

Returns true for a flavor with the MIME type "application/fits".

Specified by:

canImport in interface TableBuilder

Parameters:

flavor - the DataFlavor whose suitability as stream input is to be assessed

Returns:

true iff this builder reckons it stands a good chance of turning a stream of type flavor into a StarTable

isMagic

public static boolean isMagic(byte[] buffer)

Tests whether a given buffer contains bytes which might be the first few bytes of a FitsPlus table. The criterion is that it looks like the start of a FITS header, and the first few cards look roughly like this:

     SIMPLE  =              T
     BITPIX  =              8
     NAXIS   =              1
     NAXIS1  =            ???
     VOTMETA =              T
 

Parameters:

buffer - byte buffer containing leading few bytes of data

Returns:

true if it looks like a FitsPlus file