uk.ac.starlink.votable
Class VOElementFactory

java.lang.Object
  extended byuk.ac.starlink.votable.VOElementFactory

public class VOElementFactory
extends Object

Provides methods for constructing VOElements from a variety of sources. A VOElement can be made either from an existing DOM Element or from some non-DOM source such as a file, input stream, or SAX stream. In the latter case a DOM is built using the transformToDOM(javax.xml.transform.Source,boolean) method with no validation. There are several optimisations performed by this method which distinguish it from a DOM that you'd get if you constructed it directly; the most important ones are that the data-bearing parts (children of STREAM or TABLEDATA elements) of the XML document are not included in the built DOM, and that any reference to the VOTable DTD is resolved locally rather than making a potential network connection. You almost certainly don't need to worry about this; however if for some reason you want to work on a 'normal' DOM, or if you want validation, you can construct the DOM yourself and invoke one of the non-transforming makeVOElement methods on the result.

The various makeVOElement methods may return an object of class VOElement or of one of its subclasses, according to the name of the element in question; specific subclasses are provided only where some extra functionality is available, for instance the TableElement.getData() method of the TableElement class. One upshot of this is that a tree of VOElements need not conform to the VOTable DTD, elements of any name may be in it. Wherever an element has a name which matches an element with specific significance in a VOTable document however, such as "TABLE", it is handled accordingly.


Field Summary
static boolean STRICT_DEFAULT
          Determines whether the default strictness state is true or false when the STRICT_PROPERTY property has not been set.
static String STRICT_PROPERTY
          Property which determines the default strictness state.
 
Constructor Summary
VOElementFactory()
          Constructs a new VOElementFactory with the default storage policy.
VOElementFactory(StoragePolicy policy)
          Constructs a new VOElementFactory with a given storage policy.
 
Method Summary
 StoragePolicy getStoragePolicy()
          Returns the storage policy currently in effect.
 boolean isStrict()
          Indicates whether a strict reading of the VOTable standard is in effect.
static boolean isStrictByDefault()
          Indicates whether strict interpretation of the VOTable standard is on by default (if it has not been set explicitly).
 VOElement makeVOElement(DataSource datsrc)
          Builds a custom DOM read from a DataSource and returns a new VOElement based on its top-level element.
 VOElement makeVOElement(Document doc, String systemId)
          Returns a new VOElement based on a DOM Document node.
 VOElement makeVOElement(DOMSource dsrc)
          Returns a VOElement based on a DOM source.
 VOElement makeVOElement(Element el, String systemId)
          Returns a VOElement based on a given DOM element.
 VOElement makeVOElement(File file)
          Builds a custom DOM read from a file and returns a new VOElement based on its top-level element.
 VOElement makeVOElement(InputStream strm, String systemId)
          Builds a custom DOM from an input stream and returns a new VOElement based on its top-level element.
 VOElement makeVOElement(Source xsrc)
          Returns a VOElement based on an XML Source.
 VOElement makeVOElement(String uri)
          Builds a custom DOM read from a URI and returns a new VOElement based on its top-level element.
 VOElement makeVOElement(URL url)
          Builds a custom DOM read from a URL and returns a new VOElement based on its top-level element.
 void setStoragePolicy(StoragePolicy policy)
          Sets the storage policy.
 void setStrict(boolean strict)
          Determines whether a strict reading of the VOTable standard will be enforced.
 DOMSource transformToDOM(Source xsrc, boolean validate)
          Gets a custom DOMSource from a generic XML Source.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

STRICT_PROPERTY

public static final String STRICT_PROPERTY
Property which determines the default strictness state. Its value may be set to "true" or "false" case-insensitively. If unset, the default will be determined by the value of STRICT_DEFAULT. The return value of the isStrict() method will be set like this unless strictness is set explicitly.

See Also:
setStrict(boolean), Constant Field Values

STRICT_DEFAULT

public static boolean STRICT_DEFAULT
Determines whether the default strictness state is true or false when the STRICT_PROPERTY property has not been set. True by default.

Constructor Detail

VOElementFactory

public VOElementFactory(StoragePolicy policy)
Constructs a new VOElementFactory with a given storage policy. The StoragePolicy object is used to determine how row data which is found within the DOM will be cached.

Parameters:
policy - storage policy

VOElementFactory

public VOElementFactory()
Constructs a new VOElementFactory with the default storage policy.

See Also:
StoragePolicy.getDefaultPolicy()
Method Detail

getStoragePolicy

public StoragePolicy getStoragePolicy()
Returns the storage policy currently in effect. This is used to determine how row data found in the DOM will be stored.

Returns:
current storage policy

setStoragePolicy

public void setStoragePolicy(StoragePolicy policy)
Sets the storage policy. This determines how row data found in the DOM will be stored.

Parameters:
policy - new storage policy

makeVOElement

public VOElement makeVOElement(Element el,
                               String systemId)
Returns a VOElement based on a given DOM element. The systemId is also required since some elements (STREAM, LINK) may need it for URL resolution. It may be null however (which is fine if there are no relative URLs used in the document). If el is already a VOElement, it is just returned.

Parameters:
el - DOM element on which the new object will be based
systemId - the location of the document

makeVOElement

public VOElement makeVOElement(Document doc,
                               String systemId)
Returns a new VOElement based on a DOM Document node. The systemId is also required since some elements (STREAM, LINK) may need it for URL resolution. It may be null however (which is fine if there are no relative URLs used in the document).

Parameters:
doc - DOM document node
systemId - the location of the document
Returns:
VOElement based on doc

makeVOElement

public VOElement makeVOElement(DOMSource dsrc)
Returns a VOElement based on a DOM source.

Parameters:
dsrc - DOM source representing an Element or Document node
Returns:
VOElement based on dsrc

makeVOElement

public VOElement makeVOElement(Source xsrc)
                        throws SAXException,
                               IOException
Returns a VOElement based on an XML Source. If the source is a SAX or Stream source, this will involve a parse.

Parameters:
xsrc - the XML source representing the element
Returns:
VOElement based on xsrc
Throws:
SAXException - if xsrc is not a DOM source and there is a parse error transforming it to a DOM
IOException - if xsrc is not a DOM source and there is an I/O error transforming to a DOM

makeVOElement

public VOElement makeVOElement(InputStream strm,
                               String systemId)
                        throws SAXException,
                               IOException
Builds a custom DOM from an input stream and returns a new VOElement based on its top-level element. The systemId is also required since some elements (STREAM, LINK) may need it for URL resolution. It may be null however (which is fine if there are no relative URLs used in the document).

Parameters:
strm - stream containing XML data
systemId - the location of the document
Returns:
new VOElement
Throws:
SAXException
IOException

makeVOElement

public VOElement makeVOElement(String uri)
                        throws SAXException,
                               IOException
Builds a custom DOM read from a URI and returns a new VOElement based on its top-level element.

Parameters:
uri - location of the document
Returns:
new VOElement
Throws:
SAXException
IOException

makeVOElement

public VOElement makeVOElement(URL url)
                        throws SAXException,
                               IOException
Builds a custom DOM read from a URL and returns a new VOElement based on its top-level element.

Parameters:
url - location of the document
Returns:
new VOElement
Throws:
SAXException
IOException

makeVOElement

public VOElement makeVOElement(File file)
                        throws SAXException,
                               IOException
Builds a custom DOM read from a file and returns a new VOElement based on its top-level element.

Parameters:
file - file containing XML document
Returns:
new VOElement
Throws:
SAXException
IOException

makeVOElement

public VOElement makeVOElement(DataSource datsrc)
                        throws SAXException,
                               IOException
Builds a custom DOM read from a DataSource and returns a new VOElement based on its top-level element.

Parameters:
datsrc - data source containing XML
Returns:
new VOElement
Throws:
SAXException
IOException

transformToDOM

public DOMSource transformToDOM(Source xsrc,
                                boolean validate)
                         throws SAXException,
                                IOException
Gets a custom DOMSource from a generic XML Source. All elements in the returned DOM will be instances of VOElement or one of its specialist subclasses.

The clever bit is that during the parse (if xsrc is not already a DOMSource) it intercepts SAX events which indicate the start and end of any DATA events it finds so that they are not incorporated as part of the DOM. Such elements it parses directly on the basis of what it knows about items that crop up in VOTables. This keeps the resulting DOM to a reasonable size.

Parameters:
xsrc - input XML source
validate - whether to use a validating parser if the transformation needs to be done (that is, if xsrc is not already a DOMSource)
Returns:
a DOMSource representing the XML document held by xsrc The DOMSource's node will be either a VOElement or a VODocument
Throws:
SAXException
IOException

setStrict

public void setStrict(boolean strict)
Determines whether a strict reading of the VOTable standard will be enforced. Currently if strict is set to false the following standard-violating assumptions will be made:

Parameters:
strict - true iff you want a strict reading of the VOTable standard
See Also:
isStrict(), STRICT_PROPERTY

isStrict

public boolean isStrict()
Indicates whether a strict reading of the VOTable standard is in effect. If it has not been set explicitly, this will return the result of isStrictByDefault().

Returns:
true if the VOTable standard is being interpreted strictly
See Also:
setStrict(boolean)

isStrictByDefault

public static boolean isStrictByDefault()
Indicates whether strict interpretation of the VOTable standard is on by default (if it has not been set explicitly). The return value will be the value of the system property named STRICT_PROPERTY, or of STRICT_DEFAULT if that is not set.

Returns:
whether VOTable strict interpretation is on by default
See Also:
setStrict(boolean)

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