uk.ac.starlink.datanode.nodes

Class XMLDocument

java.lang.Object

uk.ac.starlink.datanode.nodes.XMLDocument

public class XMLDocument
extends Object

Holds a DataSource which is known to contain an XML document. DataNode implementations can provide constructors which take one of these. The idea is that the node building machinery finds out whether a DataSource represents XML (perhaps by doing a SAX parse) and stashes some basic information about it in this object - name of top-level element, IDs of the DTD, maybe a set of validation errors etc - so that the quick view can display them without any further work. It deliberately doesn't store the DOM, since keeping DOMs for all the nodes we've encountered can take up too much memory - it violates DataNode's rule about allocating large memory resources in a node's constructor before getChildren or maybe configureDetail have been called. DataNode constructors which do operate on an XMLDocument should not construct and cache a DOM themselves, though other DataNode methods may do so.

Author:

Mark Taylor (Starlink)

Field Summary

Fields

Modifier and Type	Field and Description
static String[]	ENCODINGS
static String[]	MAGICS

Constructor Summary

Constructors

Constructor and Description
XMLDocument(DataSource datsrc) Constructs a new XMLDocument from a DataSource.

Method Summary

Modifier and Type	Method and Description
DOMSource	constructDOM(boolean validate) Convenience method to get a DOM from this document, which either succeeds or throws a NoSuchDataException.
DataSource	getDataSource()
static String	getEncoding(byte[] magic) Returns what appears to be the encoding of the XML stream which starts with a given magic number.
List	getMessages()
String	getName()
Collection	getNamespaces()
String	getPublicId()
String	getSystemId()
Attributes	getTopAttributes()
String	getTopLocalName()
String	getTopNamespaceURI()
static boolean	isMagic(byte[] magic) This tests for the likely start of an XML file.
DOMSource	parseToDOM(boolean validate, ErrorHandler ehandler) Performs a parse on the data source represented by this object and returns the resulting DOM.

Methods inherited from class java.lang.Object

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

Field Detail

MAGICS

public static final String[] MAGICS

ENCODINGS

public static final String[] ENCODINGS

Constructor Detail

XMLDocument

public XMLDocument(DataSource datsrc)
            throws NoSuchDataException

Constructs a new XMLDocument from a DataSource. Enough work is done to check that the document in question appears to contain XML - if it does not, a NoSuchDataException is thrown.

Parameters:

datsrc - data source

Throws:

NoSuchDataException - if datsrc doesn't contain XML

Method Detail

getDataSource

public DataSource getDataSource()

getTopLocalName

public String getTopLocalName()

getTopNamespaceURI

public String getTopNamespaceURI()

getTopAttributes

public Attributes getTopAttributes()

getNamespaces

public Collection getNamespaces()

getMessages

public List getMessages()

getSystemId

public String getSystemId()

getPublicId

public String getPublicId()

getName

public String getName()

parseToDOM

public DOMSource parseToDOM(boolean validate,
                            ErrorHandler ehandler)
                     throws SAXException,
                            IOException

Performs a parse on the data source represented by this object and returns the resulting DOM. Note that this object does not cache such a DOM (the point of it is to stop DOMs being held on to), so only do this if you need it, and if you're going to carry on needing it, cache it.

Parameters:

validate - whether the parse should be validating

ehandler - handler for parse errors (may be null)

Returns:

DOM source containing the document this object describes

Throws:

SAXException

IOException

constructDOM

public DOMSource constructDOM(boolean validate)
                       throws NoSuchDataException

Convenience method to get a DOM from this document, which either succeeds or throws a NoSuchDataException.

Throws:

NoSuchDataException

isMagic

public static boolean isMagic(byte[] magic)

This tests for the likely start of an XML file. It's just a guess though - it can come up with false positives and (worse) false negatives.

Parameters:

magic - buffer containing the first few bytes of the stream

Returns:

true iff this looks like an XML file

getEncoding

public static String getEncoding(byte[] magic)

Returns what appears to be the encoding of the XML stream which starts with a given magic number. This is based on how we expect an XML stream to start in terms of Unicode characters (one of the strings MAGICS). The result will be one of the encoding names listed in ENCODINGS, or null if it doesn't look like the start of an XML stream in any of these encodings.

Parameters:

magic - buffer containing the first few bytes of the stream

Returns:

name of a supported encoding in which this looks like XML