Processing XML documents with Oracle JDeveloper 11g

Create a JXDocumentBuilderFactory object with the static method newInstance(). The factory object is used to obtain a parser that may be used to create a new DOM object tree. The JXDocumentBuilderFactory class is the implementation class in Oracle XDK 11g for the abstract class DocumentBuilderFactory:

JXDocumentBuilderFactory factory = (JXDocumentBuilderFactory)
JXDocumentBuilderFactory.newInstance ();

The JXDocumentBuilderFactory class extends the DocumentBuilderFactory class and provides some additional methods apart from providing some static fields and constants. The constants are used in the setAttribute(java.lang.String name, java.lang.Object value) method to set factory attribute values. The attribute names are specified as a String object and attribute values are specified as an object. The getAttribute(java.lang.String name) method may be used to retrieve the value of an attribute. Some of these attributes are listed in the following table; the attributes ERROR_STREAM and SHOW_WARNINGS will be used in the DOM parsing section:

Create a DocumentBuilder object from the factory object with the newDocumentBuilder() method. The DocumentBuilder object is used to create a new instance of a DOM Document object or to obtain a DOM Document object from an XML document. The JXDocumentBuilder class extends the DocumentBuilder class, and is an implementation class in Oracle XDK 11g for the abstract DocumentBuilder class. Cast the DocumentBuilder object, returned by the newDocumentBuilder() method, to the JXDocumentBuilder class:

JXDocumentBuilder documentBuilder = (JXDocumentBuilder)
factory.newDocumentBuilder();

Obtain a Document object from the JXDocumentBuilder object with the newDocument() method. The XMLDocument class implements the Document interface. Cast the Document object to XMLDocument:

XMLDocument xmlDocument = (XMLDocument)
documentBuilder.newDocument();

In addition to the Document interface, the XMLDocument class implements DocumentEditVAL, ElementEditVAL, DocumentEvent, DocumentTraversal, EventTarget, and NSResolver. The DocumentEditVAL and ElementEditVAL interfaces are implemented for dynamic validation as specified in the DOM 3 Validation specification and will be discussed in Chapter 8. The DocumentEvent and EventTarget interfaces are implemented for event handling and will be discussed in Chapter 7. The NSResolver interface is used for selecting namespace nodes with XPath, and will be discussed in Chapter 4.

The XMLDocument class provides some additional methods not specified in any of the implemented interfaces. Some of these methods are discussed in the following table:

Set the XML version of the DOM document object using the setVersion method, and the encoding of the DOM document using the setEncoding method:

xmlDocument.setVersion("1.0");
xmlDocument.setEncoding("UTF-8");

Create the root element catalog with the createElement(String) method. Cast the Element object returned by the createElement() method to XMLElement:

XMLElement catalogElement = (XMLElement) (xmlDocument.createElement" ("catalog"));

The XMLElement class implements the Element interface. In addition to the Element interface, XMLElement implements the ElementEditVAL and NSResolver interfaces. The ElementEditVAL interface is used for DOM 3 Validation and the NSResolver interface is used for selecting namespace nodes with XPath, which will be discussed in Chapter 4. In addition to the validation methods from the ElementEditVAL interface, the XMLElement class has the overloaded validateContent() method to validate an element. The validation methods shall be discussed in Chapter 8.

Add the root element to the XMLDocument object using the appendChild method:

xmlDocument.appendChild(catalogElement);

Next, we shall create the DOM document tree:

In the same way, add the other element and text nodes in the example XML document. The XMLDocument class provides additional methods than the Document interface methods to create XML document components other than those discussed in this section. Some of these methods are discussed in the following table:

Output the DOM document object with the XMLPrintDriver class. Create an OutputStream object to output the XML document, and create an XMLPrintDriver using the OutputStream:

OutputStream output = new FileOutputStream(new File(
"catalog.xml"));
XMLPrintDriver xmlPrintDriver = new XMLPrintDriver(new
PrintWriter(output));

Output the XML document with the printDocument(XMLDocument) method. Flush the output stream using the flush() method and close the output stream using the close() method:

xmlPrintDriver.printDocument(xmlDocument);
xmlPrintDriver.flush();
xmlPrintDriver.close();

XMLPrintDriver may be used to print not only an XMLDocument node, but other nodes as well. The print methods in the XMLPrintDriver class are listed in the following table:

To run the CreateXMLDocument.java application in JDeveloper, right-click on CreateXMLDocument.java in Application Navigator and select Run.

The XML document gets generated. Select View|Refresh to add the generated XML document, catalog.xml, to the Application Navigator.

The complete CreateXMLDocument.java Java application is listed here with brief notes that explain the different sections of the application:

Create a JXDcoumentBuilderFactory object with the static method newInstance(). The factory object is used to obtain a parser that may be used to create a DOM document tree from an XML document:

JXDocumentBuilderFactory factory = (JXDocumentBuilderFactory) JXDocumentBuilderFactory.newInstance();

Set the ERROR_STREAM and SHOW_WARNINGS attributes on the factory object with the setAttribute() method. The ERROR_STREAM attribute specifies the error stream, while the SHOW_WARNINGS attribute specifies if warnings are to be shown. The value of the ERROR_STREAM attribute is an OutputStream object or a PrintWriter object. The value of the SHOW_WARNINGS attribute is a Boolean, which can be set to Boolean.TRUE or Boolean.FALSE. With the OutputStream or PrintWriter specified in the ERROR_STREAM attribute, parsing errors (if any) get outputted to the specified file. If ErrorHandler is also set, ERROR_STREAM is not used. The SHOW_WARNINGS attribute outputs warnings also:

factory.setAttribute(JXDocumentBuilderFactory.ERROR_STREAM,
new FileOutputStream(new File("c:/output/errorStream.txt")));
factory.setAttribute(JXDocumentBuilderFactory.SHOW_WARNINGS,
Boolean.TRUE);

Create a JXDocumentBuilder object from the factory object by first creating a DocumentBuilder object with newDocumentBuilder() method and subsequently casting the DocumentBuilder object to JXDocumentBuilder. JXDocumentBuilder is the implementation class in Oracle XDK 11g for the abstract class DocumentBuilder:

JXDocumentBuilder documentBuilder = (JXDocumentBuilder) factory.newDocumentBuilder();

The JXDocumentBuilder object is used to create a DOM document object from an XML document. A Document object may be obtained using the JXDocumentBuilder object with one of the parse() methods in the JXDocumentBuilder class. The input to the parser may be specified as InputSource, InputStream, File object, or a String URI. Create an InputStream for the example XML document and parse the document with the parse(InputStream) method:

InputStream input = new FileInputStream(new File("catalog.xml"));
XMLDocument xmlDocument = (XMLDocument) (documentBuilder.parse(input));

The parse() methods of the JXDocumentBuilder object return a Document object, which may be cast to an XMLDocument object, as the XMLDocument class implements the Document interface.

Output the encoding in the XML document using the getEncoding method, and output the version of the XML document using the getVersion method:

System.out.println("Encoding: " + xmlDocument.getEncoding());
System.out.println("Version: " + xmlDocument.getVersion());

The XMLDocument class has various getter methods to retrieve elements in a document. Some of these methods are listed in the following table:

As an example, retrieve title elements in the namespace http://xdk.com/catalog/journal using the getElementsByTagNameNS method:

NodeList namespaceNodeList = xmlDocument.getElementsByTagNameNS("http://xdk.com/catalog/journal","title");

Iterate over the NodeList to output element namespace, element namespace prefix, element tag name, and element text. The getNamespaceURI() method returns the namespace URI of an element. The getPrefix() method returns the prefix of an element in a namespace. The getTagName() method returns the element tag name. Element text is obtained by first obtaining the text node within the element node using the getFirstChild() method and subsequently the value of the text node:

for (int i = 0; i < namespaceNodeList.getLength(); i++) {
XMLElement namespaceElement = (XMLElement) namespaceNodeList.item(i);
System.out.println("Namespace URI: " +
namespaceElement.getNamespaceURI());
System.out.println("Namespace Prefix: " +
namespaceElement.getPrefix());
System.out.println("Element Name: " +
namespaceElement.getTagName());
System.out.println("Element text: " +
namespaceElement.getFirstChild().getNodeValue());
}

Obtain the root element in the XML document with the getDocumentElement() method. The getDocumentElement method returns an Element object that may be cast to an XMLElement object if any of the methods defined only in the XMLElement class are to be used. The Element object is not required to be cast to an XMLElement object. We have cast the Element object to XMLElement as XMLElement is Oracle XDK 11g's implementation class for the Element interface, and we are discussing Oracle XDK 11g:

XMLElement rootElement = (XMLElement)
(xmlDocument.getDocumentElement());
System.out.println("Root Element is: " + rootElement.getTagName());

Next, we shall iterate over all the subnodes of the root element. Obtain a NodeList of subnodes of the root element with the getChildNodes() method. Create a method iterateNodeList() to iterate over the subnodes of an Element. Iterate over the NodeList and recursively obtain the subelements of the elements in the NodeList. The method hasChildNodes() tests to see if a node has subnodes. Ignorable whitespace is also considered a node, but we are mainly interested in the subelements in a node. The NodeList interface method getLength() returns the length of a node list, and method item(int) returns the Node at a specified index. As class XMLNode is Oracle XDK 11g's implementation class for the Node interface, cast the Node object to XMLNode:

if (rootElement.hasChildNodes()) {
NodeList nodeList = rootElement.getChildNodes();
iterateNodeList(rootElement, nodeList);
}

If a node is of type element, the tag name of the element may be retrieved. Node type is obtained with the getNodeType() method, which returns a short value. The Node interface provides static fields for different types of nodes. The different types of nodes in an XML document are listed in the following table:

For an element node, cast the node to XMLElement and output the element tag name:

if (node.getNodeType() == XMLNode.ELEMENT_NODE) {
XMLElement element = (XMLElement) node;
System.out.println("Element Tag Name:"+
element.getTagName))
}

The attributes in a element node are retrieved with the getAttributes() method, which returns a NamedNodeMap of attributes. The getLength() method of NamedNodeMap returns the length of an attribute node list. The method item(int) returns an Attr object for the attribute at the specified index. As class XMLAttr implements the Attr interface, cast the Attr object to XMLAttr. Iterate over the NamedNodeMap to output the attribute name and value. The hasAttributes() method tests if an element node has attributes:

if (element.hasAttributes()) {
NamedNodeMap attributes = element.getAttributes();
for (int i = 0; i < attributes.getLength(); i++) {
XMLAttr attribute = (XMLAttr)attributes.item(i);
System.out.println(" Attribute: " + attribute.getName() +
" with value " +attribute.getValue());
}
}

The complete DOMParserApp.java Java application code listing is listed as follows with notes about the different sections in the Java class:

To demonstrate error handling with the ERROR_STREAM attribute, add an error in the example XML document. For example, remove a </journal> tag. Run the DOMParserApp.java application in JDeveloper. An error message gets outputted to the file specified in the ERROR_STREAM attribute:

<Line 15, Column 10>: XML-20121: (Fatal Error) End tag
does not match start tag 'journal'.

Create a JXSAXParserFactory object with the static method newInstance(). The newInstance() method returns a SAXParserFactory object that may be cast to JXSAXParserFactory as the JXSAXParserFactory class extends the SAXParserFactory class. Why cast, you might ask? We are using Oracle XDK 11g's implementation classes for various standard interfaces and abstract classes.

JXSAXParserFactory factory = (JXSAXParserFactory) JXSAXParserFactory.newInstance();

The factory object is used to obtain a SAX parser that may be used to parse an XML document.

Create a SAXParser object from the factory object with the newSAXParser() method. As class JXSAXParser extends the SAXParser class, a SAXParser object may be cast to JXSAXParser:

JXSAXParser saxParser = (JXSAXParser) factory.newSAXParser();

Create an InputStream for the XML document to parse, and parse the XML document with one of the parse() methods in the SAXParser class. The parse methods take an XML document in the form of InputSource, InputStream, URI, or File, and an event handler such as the DefaultHandler.

InputStream input = new FileInputStream(new File("catalog.xml"));
saxParser.parse(input, this);

The DefaultHandler class provides the parsing event notification methods and error handling methods. Event notification and error handling methods may be overridden in the SAX parsing application for application-specific events and error handling. Some of the event notification methods in the DefaultHandler class are listed in the following table:

In the SAXParserApp.java application, some of the notification methods are overridden to output the event type, element name, element attributes, and element text. For example, the attributes represented by the Attributes object in the startElement(java.lang.String uri, java.lang.String localName, java.lang.String qName, Attributes atts) method may be iterated to output the attribute name, namespace URI, and attribute value:

for (int i = 0; i < atts.getLength(); i++) {
System.out.println("Attribute QName:" +atts.getQName(i));
System.out.println("Attribute Local Name:"+ atts.getLocalName(i));
System.out.println("Attribute Namespace URI:" + atts.getURI(i));
System.out.println("Attribute Value:"+atts.getValue(i));
}

The error handler methods in DefaultHandler may also be overridden. In the SAXParserApp.java application, the error handler methods are overridden to output the error message. We shall demonstrate error handling in a SAX parsing application with an example. Error handler methods in the DefaultHandler class are listed in the following table:

The SAXParserApp.java application is listed as follows with notes about the different sections of the Java class:

The output from the SAX parsing application lists the SAX events, elements, and attributes in the parsed XML document.

The complete output from the SAX parsing application is listed as follows:

SAX Event : Start Document
SAX Event : Start Element
Element QName:catalog
Element Local Name:catalog
Element Namespace URI:
SAX Event : Text
SAX Event : Start Element
Element QName:journal:journal
Element Local Name:journal
Element Namespace URI:http://xdk.com/catalog/journal
Attribute QName:journal:title
Attribute Local Name:title
Attribute Namespace URI:http://xdk.com/catalog/journal
Attribute Value:Oracle Magazine
Attribute QName:journal:publisher
Attribute Local Name:publisher
Attribute Namespace URI:http://xdk.com/catalog/journal
Attribute Value:Oracle Publishing
Attribute QName:journal:edition
Attribute Local Name:edition
Attribute Namespace URI:http://xdk.com/catalog/journal
Attribute Value:March-April 2008
Attribute QName:xmlns:journal
Attribute Local Name:journal
Attribute Namespace URI:http://www.w3.org/2000/xmlns/
Attribute Value:http://xdk.com/catalog/journal
SAX Event : Text
SAX Event : Start Element
Element QName:journal:article
Element Local Name:article
Element Namespace URI:http://xdk.com/catalog/journal
Attribute QName:journal:section
Attribute Local Name:section
Attribute Namespace URI:http://xdk.com/catalog/journal
Attribute Value:Oracle Developer
SAX Event : Text
SAX Event : Start Element
Element QName:journal:title
Element Local Name:title
Element Namespace URI:http://xdk.com/catalog/journal
SAX Event : Text
Text:Declarative Data Filtering
SAX Event : End Element
Element QName:journal:title
SAX Event : Text
SAX Event : Start Element
Element QName:journal:author
Element Local Name:author
Element Namespace URI:http://xdk.com/catalog/journal
SAX Event : Text
Text:Steve Muench
SAX Event : End Element
Element QName:journal:author
SAX Event : Text
SAX Event : End Element
Element QName:journal:article
SAX Event : Text
SAX Event : End Element
Element QName:journal:journal
SAX Event : Text
SAX Event : Start Element
Element QName:journal
Element Local Name:journal
Element Namespace URI:
Attribute QName:title
Attribute Local Name:title
Attribute Namespace URI:
Attribute Value:Oracle Magazine
Attribute QName:publisher
Attribute Local Name:publisher
Attribute Namespace URI:
Attribute Value:Oracle Publishing
Attribute QName:edition
Attribute Local Name:edition
Attribute Namespace URI:
Attribute Value:September-October 2008
SAX Event : Text
SAX Event : Start Element
Element QName:article
Element Local Name:article
Element Namespace URI:
Attribute QName:section
Attribute Local Name:section
Attribute Namespace URI:
Attribute Value:FEATURES
SAX Event : Text
SAX Event : Start Element
Element QName:title
Element Local Name:title
Element Namespace URI:
SAX Event : Text
Text:Share 2.0
SAX Event : End Element
Element QName:title
SAX Event : Text
SAX Event : Start Element
Element QName:author
Element Local Name:author
Element Namespace URI:
SAX Event : Text
Text:Alan Joch
SAX Event : End Element
Element QName:author
SAX Event : Text
SAX Event : End Element
Element QName:article
SAX Event : Text
SAX Event : End Element
Element QName:journal
SAX Event : Text
SAX Event : End Element
Element QName:catalog
SAX Event : End Document

To demonstrate error handling, add an error in the example XML document. For example, remove a </journal> node, as we did earlier. Run the SAXParserApp.java application in JDeveloper. An error message gets outputted:

Fatal Error:<Line 15, Column 10>: XML-20121: (Fatal Error) End tag does not match start tag 'journal'.