uk.ac.starlink.votable
Class FitsPlusTableBuilder

java.lang.Object
  extended by 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
See Also:
FitsPlusTableWriter

Constructor Summary
FitsPlusTableBuilder()
          Default constructor.
FitsPlusTableBuilder(WideFits wide)
          Constructor.
 
Method Summary
 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.
 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

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

Copyright © 2004 CLRC: Central Laboratory of the Research Councils. All rights reserved.