uk.ac.starlink.fits
Class FitsTableBuilder

java.lang.Object
  extended by uk.ac.starlink.fits.FitsTableBuilder
All Implemented Interfaces:
MultiTableBuilder, TableBuilder

public class FitsTableBuilder
extends java.lang.Object
implements TableBuilder, MultiTableBuilder

Implementation of the TableBuilder interface which gets StarTables from FITS files.

The table implementation used by uncompressed binary FITS tables stored on disk maps the file into memory (MappedByteBuffer) rather than reading the stream as such; this makes table construction very fast and cheap on memory, regardless of storage policy. This behaviour can be inhibited by referring to the file location as a URL (e.g. "file:spec23.fits" rather than "spec23.fits"), which fools the handler into thinking that it can't be mapped.


Constructor Summary
FitsTableBuilder()
           
 
Method Summary
static StarTable attemptReadTable(nom.tam.util.ArrayDataInput strm, boolean wantRandom, DataSource datsrc, long[] pos)
          Reads the next header, and returns a StarTable based on it if it represents a table.
 boolean canImport(java.awt.datatransfer.DataFlavor flavor)
          Returns true for a flavor with the MIME type "application/fits".
 java.lang.String getFormatName()
          Returns "FITS".
 StarTable makeStarTable(DataSource datsrc, boolean wantRandom, StoragePolicy policy)
          Creates a StarTable from a DataSource which refers to a FITS file or stream.
 TableSequence makeStarTables(DataSource datsrc, StoragePolicy policy)
          Constructs a sequence of StarTables based on a given DataSource.
 void streamStarTable(java.io.InputStream istrm, TableSink sink, java.lang.String extnum)
          Reads a FITS table from an input stream and writes it to a sink.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FitsTableBuilder

public FitsTableBuilder()
Method Detail

getFormatName

public java.lang.String getFormatName()
Returns "FITS".

Specified by:
getFormatName in interface TableBuilder
Returns:
one-word description of this handler's format

makeStarTable

public StarTable makeStarTable(DataSource datsrc,
                               boolean wantRandom,
                               StoragePolicy policy)
                        throws java.io.IOException
Creates a StarTable from a DataSource which refers to a FITS file or stream. If the source has a position attribute, it will be interpreted as an integer indicating which HDU the table is in. The first HDU is number 0 (though being a primary HDU this one can't hold a table). If there is no position, the first HDU which does hold a table is used.

Specified by:
makeStarTable in interface TableBuilder
Parameters:
datsrc - the source of the FITS table data
wantRandom - whether a random-access table is preferred
policy - a StoragePolicy object which may be used to supply scratch storage if the builder needs it
Returns:
a new StarTable based on datsrc, or null if it doesn't look like a FITS table
Throws:
TableFormatException - if the table is not of a kind that can be handled by this handler
java.io.IOException - if an unexpected I/O error occurs during processing

makeStarTables

public TableSequence makeStarTables(DataSource datsrc,
                                    StoragePolicy policy)
                             throws java.io.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
policy - 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
java.io.IOException - if an unexpected I/O error occurs during processing

canImport

public boolean canImport(java.awt.datatransfer.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

streamStarTable

public void streamStarTable(java.io.InputStream istrm,
                            TableSink sink,
                            java.lang.String extnum)
                     throws java.io.IOException
Reads a FITS table from an input stream and writes it to a sink.

Specified by:
streamStarTable in interface TableBuilder
Parameters:
istrm - input stream containing the FITS data
sink - destination for table data
extnum - may contain a string representation of the HDU number in which the required table is found (otherwise the first table HDU will be used)
Throws:
TableFormatException - if the table can't be streamed or the data is malformed
java.io.IOException - if some other error occurs

attemptReadTable

public static StarTable attemptReadTable(nom.tam.util.ArrayDataInput strm,
                                         boolean wantRandom,
                                         DataSource datsrc,
                                         long[] pos)
                                  throws nom.tam.fits.FitsException,
                                         java.io.IOException
Reads the next header, and returns a StarTable based on it if it represents a table. If a StarTable is returned, it may not be safe to use the supplied input stream subsequently for other purposes. If the next HDU is some non-table type, null is returned and the stream is advanced to the end of that HDU; in this case the stream may continue to be used (e.g. for further calls to this method).

On exit, the first element of the pos array contains the position after the current HDU.

Parameters:
strm - stream to read from, positioned at the start of an HDU (before the header)
wantRandom - whether a random-access table is preferred
datsrc - a DataSource which can supply the data in strm
pos - a 1-element array holding the position in datsrc at which strm is positioned - it's an array so it can be updated by this routine (sorry)
Returns:
a StarTable made from the HDU at the start of strm or null
Throws:
nom.tam.fits.FitsException
java.io.IOException

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