Headline

In-memory XML processing in Language:Java with Technology:DOM

Characteristics

Companies are represented in Language:XML and the object model of Technology:DOM is used to represent and process XML documents in memory. In particular, operations on companies are implemented in Java on top of DOM objects. Such objects are easily queried - as needed for Feature:Total. As DOM objects also mutable, Feature:Cut is implemented as an impure function.

Illustration

The data model is implemented as xml files (sampleCompany.xml) that conform to a schema (Company.xsd).

Feature:Open serialization is implemented by loading and storing a Technology:DOM Document object:

	/**
	 * Parse a file and return the Document object
	 */
	public static Document loadDocument(String filename) {
		try {
			// Create a builder factory
			DocumentBuilderFactory factory = DocumentBuilderFactory
					.newInstance();

			// Create the builder
			DocumentBuilder builder = factory.newDocumentBuilder();

			// Deserialization by parsing
			Document doc = builder.parse(new File(filename));

			// Done
			return doc;

		} catch (SAXException e) {
		} catch (ParserConfigurationException e) {
		} catch (IOException e) {
		}
		// Return null for any sort of problem
		return null;
	}
	/**
	 * Save a document to a file.
	 */
	public static boolean saveDocument(Document doc, String filename) {

		try {
			// Prepare the DOM document for writing
			Source source = new DOMSource(doc);

			// Prepare the output file
			File file = new File(filename);
			Result result = new StreamResult(file);

			// Creater a transformer factory
			TransformerFactory xfactory = TransformerFactory.newInstance();

			// Create a transformer
			Transformer transformer = xfactory.newTransformer();

			// Force pretty printing
			transformer.setOutputProperty(OutputKeys.METHOD, "xml");
			transformer.setOutputProperty(OutputKeys.INDENT, "yes");
			transformer.setOutputProperty(
					"{http://xml.apache.org/xslt}indent-amount", "2");
			transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");

			// Serialization by transformation
			transformer.transform(source, result);

			// Done
			return true;

		} catch (TransformerConfigurationException e) {
		} catch (TransformerException e) {
		}
		// Return false for any sort of problem
		return false;
	}

A method to validate the deserialized xml with the Company XSD schema is implemented by a DOM Validator:

	/**
	 * return true if document is a valid company
	 * 
	 */
	public static boolean isValidXml(String xmlFile, String xsdFile) {
		Schema schema = null;
		// Create a builder factory
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

		factory.setNamespaceAware(true);

		// Create a factory for validation
		String language = XMLConstants.W3C_XML_SCHEMA_NS_URI;
		SchemaFactory schemaFactory = SchemaFactory.newInstance(language);

		try {
			// Create schema from xsd file
			schema = schemaFactory.newSchema(new File(xsdFile));
			// Create validator
			Validator validator = schema.newValidator();
			// Create DocumentBuilder
			DocumentBuilder builder = factory.newDocumentBuilder();
			// Create document from xml file
			Document doc = builder.parse(new File(xmlFile));
			// validate xml file with xsd schema
			validator.validate(new DOMSource(doc));
			return true;
		} catch (SAXException e) {
			System.err.println(e);
		} catch (IOException e) {
			System.err.println(e);
		} catch (ParserConfigurationException e) {
			System.err.println(e);
		}
		return false;
	}

Feature:Total and Feature:Cut are implemented using methods of Technology:DOM's Document class:

    public static double total(Document doc) {
        // The aggregation variable 
        double total = 0;

        // Get the matching elements
        NodeList nodelist = doc.getElementsByTagName("salary");

        // Process the elements in the nodelist
        for (int i=0; i<nodelist.getLength(); i++) {
            // Get element
            Element elem = (Element)nodelist.item(i);
            total += Double.parseDouble(elem.getTextContent());
        }
        return total;
    }
    public static void cut(Document doc) {
        // Get the matching elements
        NodeList nodelist = doc.getElementsByTagName("salary");

        // Process the elements in the nodelist
        for (int i=0; i<nodelist.getLength(); i++) {

            // Get element
            Element elem = (Element)nodelist.item(i);

            // Transform content of element
            double value = parseDouble(elem.getTextContent());
            elem.setTextContent(Double.toString(value / 2));
        }
    }

Test cases are implemented for all Namespace:Features.

Relationships

For DOM-like implementations of in-memory XML processing see Contribution:dom, Contribution:jdom and Contribution:xom.

For a query-based implementation of in-memory XML processing see Contribution:xpathAPI.

For push-based XML processing see Contribution:sax.

For Object/XML mapping see Contribution:jaxbChoice (XSD with choice for different subunits), Contribution:jaxbComposition (XSD with object composition), Contribution:jaxbExtension (XSD with type extension) and Contribution:jaxbSubstitution (XSD with substitution groups).

Architecture

The contribution follows a standardized structure:

  • inputs contains input files for tests
  • src/main/java contains the following packages:
  • src/test/java contains the following packages:

Usage

This contribution uses Technology:Gradle for building. Technology:Eclipse is supported.

See https://github.com/101companies/101simplejava/blob/master/README.md

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