uk.ac.starlink.hapi

Class HapiTableBuilder

java.lang.Object

uk.ac.starlink.table.formats.DocumentedTableBuilder

uk.ac.starlink.hapi.HapiTableBuilder

All Implemented Interfaces:

Documented, DocumentedIOHandler, TableBuilder

public class HapiTableBuilder
extends DocumentedTableBuilder

TableBuilder implementation for HAPI data streams. This only works for binary- and csv-format streams, and they must contain a HAPI header as obtained using the HAPI Data endpoint with include=header.

Since:

12 Jan 2024

Author:

Mark Taylor

Constructor Summary

Constructors

Constructor and Description
HapiTableBuilder()

Method Summary

Modifier and Type	Method and Description
boolean	canImport(DataFlavor flavor) Indicates whether this builder is able to turn a resource of media type indicated by flavor into a table.
boolean	canStream() Indicates whether this handler can read tables from a stream.
boolean	docIncludesExample() Indicates whether the serialization of some (short) example table should be added to the user documentation for this handler.
String	getFormatName() Returns the name of the format which can be read by this handler.
String	getXmlDescription() Returns user-directed documentation in XML format.
static boolean	isMagic(byte[] buf) Attempts to determine whether a stream contains a HAPI table including header.
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.
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 uk.ac.starlink.table.formats.DocumentedTableBuilder

getExtensions

Methods inherited from class java.lang.Object

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

Methods inherited from interface uk.ac.starlink.table.formats.DocumentedIOHandler

matchesExtension, readText, toLink

Constructor Detail

HapiTableBuilder

public HapiTableBuilder()

Method Detail

canStream

public boolean canStream()

Description copied from class: DocumentedTableBuilder

Indicates whether this handler can read tables from a stream.

Specified by:

canStream in class DocumentedTableBuilder

Returns:

true iff this handler can read from streams

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.

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

Overrides:

looksLikeFile in class DocumentedTableBuilder

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

canImport

public boolean canImport(DataFlavor flavor)

Description copied from interface: TableBuilder

Indicates whether this builder is able to turn a resource of media type indicated by flavor into a table. It should return true if it thinks that its TableBuilder.streamStarTable(java.io.InputStream, uk.ac.starlink.table.TableSink, java.lang.String) method stands a reasonable chance of successfully constructing a StarTable from a DataSource whose input stream is described by the DataFlavor flavor. It will typically make this determination based on the flavor's MIME type.

This method should only return true if the flavor looks like it is targeted at this builder; for instance a builder which uses a text-based format should return false for a flavor which indicates a MIME type of text/plain.

This method is used in supporting drag and drop functionality (see StarTableFactory.canImport(java.awt.datatransfer.DataFlavor[])).

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

docIncludesExample

public boolean docIncludesExample()

Description copied from interface: DocumentedIOHandler

Indicates whether the serialization of some (short) example table should be added to the user documentation for this handler. Binary formats, or instances for which the Documented.getXmlDescription() method already includes some example output, should return false.

Returns:

true if the user documentation would benefit from the addition of an example serialization

getXmlDescription

public String getXmlDescription()

Description copied from interface: Documented

Returns user-directed documentation in XML format.

The output should be a sequence of one or more <P> elements, using XHTML-like XML. Since rendering may be done in a number of contexts however, use of the full range of XHTML elements is discouraged. Where possible, the content should stick to simple markup such as the elements P, A, UL, OL, LI, DL, DT, DD EM, STRONG, I, B, CODE, TT, PRE.

Returns:

XML description of this object

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.

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

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.

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

isMagic

public static boolean isMagic(byte[] buf)

Attempts to determine whether a stream contains a HAPI table including header. False positives are quite possible.

Returns:

false if it's definitely not a suitable HAPI stream