The mapping in the JavaTM programming language for the SQL XML type. XML is a built-in type that stores an XML value as a column value in a row of a database table. By default, drivers implement an SQLXML object as a logical pointer to the XML data rather than the data itself. An SQLXML object is valid for the duration of the transaction in which it was created.

The SQLXML interface provides methods for accessing the XML value as a String, a Reader or Writer, or as a Stream. The XML value may also be accessed through a Source or set as a Result, which are used with XML Parser APIs such as DOM, SAX, and StAX, as well as with XSLT transforms and XPath evaluations.

Methods in the interfaces ResultSet, CallableStatement, and PreparedStatement, such as getSQLXML allow a programmer to access an XML value. In addition, this interface has methods for updating an XML value.

The XML value of the SQLXML instance may be obtained as a BinaryStream using

  SQLXML sqlxml = resultSet.getSQLXML(column);
  InputStream binaryStream = sqlxml.getBinaryStream();

For example, to parse an XML value with a DOM parser:

  DocumentBuilder parser = DocumentBuilderFactory.newInstance().newDocumentBuilder();
  Document result = parser.parse(binaryStream);

or to parse an XML value with a SAX parser to your handler:

  SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
  parser.parse(binaryStream, myHandler);

or to parse an XML value with a StAX parser:

  XMLInputFactory factory = XMLInputFactory.newInstance();
  XMLStreamReader streamReader = factory.createXMLStreamReader(binaryStream);

Because databases may use an optimized representation for the XML, accessing the value through getSource() and setResult() can lead to improved processing performance without serializing to a stream representation and parsing the XML.

For example, to obtain a DOM Document Node:

  DOMSource domSource = sqlxml.getSource(DOMSource.class);
  Document document = (Document) domSource.getNode();

or to set the value to a DOM Document Node to myNode:

  DOMResult domResult = sqlxml.setResult(DOMResult.class);
  domResult.setNode(myNode);

or, to send SAX events to your handler:

  SAXSource saxSource = sqlxml.getSource(SAXSource.class);
  XMLReader xmlReader = saxSource.getXMLReader();
  xmlReader.setContentHandler(myHandler);
  xmlReader.parse(saxSource.getInputSource());

or, to set the result value from SAX events:

  SAXResult saxResult = sqlxml.setResult(SAXResult.class);
  ContentHandler contentHandler = saxResult.getXMLReader().getContentHandler();
  contentHandler.startDocument();
  // set the XML elements and attributes into the result
  contentHandler.endDocument();

or, to obtain StAX events:

  StAXSource staxSource = sqlxml.getSource(StAXSource.class);
  XMLStreamReader streamReader = staxSource.getXMLStreamReader();

or, to set the result value from StAX events:

  StAXResult staxResult = sqlxml.setResult(StAXResult.class);
  XMLStreamWriter streamWriter = staxResult.getXMLStreamWriter();

or, to perform XSLT transformations on the XML value using the XSLT in xsltFile output to file resultFile:

  File xsltFile = new File("a.xslt");
  File myFile = new File("result.xml");
  Transformer xslt = TransformerFactory.newInstance().newTransformer(new StreamSource(xsltFile));
  Source source = sqlxml.getSource(null);
  Result result = new StreamResult(myFile);
  xslt.transform(source, result);

or, to evaluate an XPath expression on the XML value:

  XPath xpath = XPathFactory.newInstance().newXPath();
  DOMSource domSource = sqlxml.getSource(DOMSource.class);
  Document document = (Document) domSource.getNode();
  String expression = "/foo/@bar";
  String barValue = xpath.evaluate(expression, document);

To set the XML value to be the result of an XSLT transform:

  File sourceFile = new File("source.xml");
  Transformer xslt = TransformerFactory.newInstance().newTransformer(new StreamSource(xsltFile));
  Source streamSource = new StreamSource(sourceFile);
  Result result = sqlxml.setResult(null);
  xslt.transform(streamSource, result);

Any Source can be transformed to a Result using the identity transform specified by calling newTransformer():

  Transformer identity = TransformerFactory.newInstance().newTransformer();
  Source source = sqlxml.getSource(null);
  File myFile = new File("result.xml");
  Result result = new StreamResult(myFile);
  identity.transform(source, result);

To write the contents of a Source to standard output:

  Transformer identity = TransformerFactory.newInstance().newTransformer();
  Source source = sqlxml.getSource(null);
  Result result = new StreamResult(System.out);
  identity.transform(source, result);

To create a DOMSource from a DOMResult:

   DOMSource domSource = new DOMSource(domResult.getNode());

Incomplete or invalid XML values may cause an SQLException when set or the exception may occur when execute() occurs. All streams must be closed before execute() occurs or an SQLException will be thrown.

Reading and writing XML values to or from an SQLXML object can happen at most once. The conceptual states of readable and not readable determine if one of the reading APIs will return a value or throw an exception. The conceptual states of writable and not writable determine if one of the writing APIs will set a value or throw an exception.

The state moves from readable to not readable once free() or any of the reading APIs are called: getBinaryStream(), getCharacterStream(), getSource(), and getString(). Implementations may also change the state to not writable when this occurs.

The state moves from writable to not writable once free() or any of the writing APIs are called: setBinaryStream(), setCharacterStream(), setResult(), and setString(). Implementations may also change the state to not readable when this occurs.

All methods on the SQLXML interface must be fully implemented if the JDBC driver supports the data type.

HSQLDB-Specific Information:

Starting with HSQLDB 2.0, a rudimentary client-side SQLXML interface implementation (this class) is supported for local use when the product is built and run under JDK 1.6+ and the SQLXML instance is constructed as the result of calling JDBCConnection.createSQLXML().

SQLXML instances retrieved in such a fashion are initially write-only, with the lifecycle of read and write availability constrained in accordance with the documentation of the interface methods.

When build and run under JDK 1.6+, it is also possible to retrieve read-only SQLXML instances from JDBCResultSet.getSQLXML(...), given that the underlying data can be converted to an XML Document Object Model (DOM).

However, at the time of this writing (2007-06-12) it is not yet possible to store SQLXML objects directly into an HSQLDB database or to use them directly for HSQLDB statement parameterization purposes. This is because the SQLXML data type is not yet natively supported by the HSQLDB engine. Instead, a JDBCSQLXML instance must first be read as a string, binary input stream, character input stream and so on, which can then be used for such purposes.

Here is the current read/write availability lifecycle for JDBCSQLXML:

Lifecycle

Origin	Initially	After 1st Write	After 1st Read	After 1st Free
org.hsqldb.jdbc.JDBCConnection.createSQLXML()	Write-only	Read-only	Not readable or writable	Not readable or writable
org.hsqldb.jdbc.JDBCResultSet.getSQLXML(...)	Read-only	N/A	Not readable or writable	Not readable or writable

  javax.xml.transform.dom.DOMSource - returns a DOMSource
  javax.xml.transform.sax.SAXSource - returns a SAXSource
  javax.xml.transform.stax.StAXSource - returns a StAXSource
  javax.xml.transform.stream.StreamSource - returns a StreamSource

  javax.xml.transform.dom.DOMResult - returns a DOMResult
  javax.xml.transform.sax.SAXResult - returns a SAXResult
  javax.xml.transform.stax.StAXResult - returns a StAXResult
  javax.xml.transform.stream.StreamResult - returns a StreamResult