Java API for XML Processing

The DOM interface parses an entire XML document and constructs a complete in-memory representation of the document using the classes and modeling the concepts found in the Document Object Model Level 2 Core Specification. The DOM parser is called a , as it builds an in-memory Document representation. The is created by the . The creates an instance - a tree structure containing nodes in the XML Document. Each tree node in the structure implements the interface. Among the many different types of tree nodes, each representing the type of data found in an XML document, the most important include: • element nodes that may have attributes • text nodes representing the text found between the start and end tags of a document element. == SAX interface ==

The creates the SAX parser, called the . Unlike the DOM parser, the SAX parser does not create an in-memory representation of the XML document and so runs faster and uses less memory. Instead, the SAX parser informs clients of the XML document structure by invoking callbacks, that is, by invoking methods on an instance provided to the parser. This way of accessing document is called Streaming XML. The DefaultHandler class implements the , the , the , and the interfaces. Most clients will be interested in methods defined in the ContentHandler interface that are called when the SAX parser encounters the corresponding elements in the XML document. The most important methods in this interface are: • and methods that are called at the start and end of a XML document. • startElement() and endElement() methods that are called at the start and end of a document element. • characters() method that is called with the text data contents contained between the start and end tags of an XML document element. Clients provide a subclass of the DefaultHandler that overrides these methods and processes the data. This may involve storing the data into a database or writing it out to a stream. During parsing, the parser may need to access external documents. It is possible to store a local cache for frequently used documents using an XML Catalog. This was introduced with Java 1.3 in May 2000. == StAX interface ==

StAX was designed as a median between the DOM and SAX interface. In its metaphor, the programmatic entry point is a cursor that represents a point within the document. The application moves the cursor forward - 'pulling' the information from the parser as it needs. This is different from an event based API - such as SAX - which 'pushes' data to the application - requiring the application to maintain state between events as necessary to keep track of location within the document. == XSLT interface ==

The XML Stylesheet Language for Transformations, or XSLT, allows for conversion of an XML document into other forms of data. JAXP provides interfaces in package allowing applications to invoke an XSLT transformation. This interface was originally called TrAX (Transformation API for XML), and was developed by an informal collaboration between the developers of a number of Java XSLT processors. Main features of the interface are • a factory class allowing the application to select dynamically which XSLT processor it wishes to use (, , . • methods on the factory class to create a object, representing the compiled form of a stylesheet. This is a thread-safe object that can be used repeatedly, in series or in parallel, to apply the same stylesheet to multiple source documents (or to the same source document with different parameters) (), also , ), a method on the object to create a , representing the executable form of a stylesheet () This cannot be shared across threads, though it is serially reusable. The provides methods to set stylesheet parameters and serialization options (for example, whether output should be indented), and a method to actually run the transformation. (). Two abstract interfaces and are defined to represent the input and output of the transformation. This is a somewhat unconventional use of Java interfaces, since there is no expectation that a processor will accept any class that implements the interface - each processor can choose which kinds of or it is prepared to handle. In practice all JAXP processors supports several standard kinds of Source (, ) and several standard kinds of Result (, ) and possibly other implementations of their own. Example The most primitive but complete example of XSLT transformation launching may look like this: /* file src/examples/xslt/XsltDemo.java */ package examples.xslt; import java.io.StringReader; import java.io.StringWriter; import javax.xml.transform.Transformer; import javax.xml.transform.TransformerException; import javax.xml.transform.TransformerFactory; import javax.xml.transform.TransformerFactoryConfigurationError; import javax.xml.transform.stream.StreamResult; import javax.xml.transform.stream.StreamSource; public class XsltDemo { public static void main(String[] args) throws TransformerFactoryConfigurationError, TransformerException { //language=xslt String xsltResource = """ world """; // language=XML String xmlSourceResource = """ """; StringWriter xmlResultResource = new StringWriter(); Transformer xmlTransformer = TransformerFactory.newInstance().newTransformer( new StreamSource(new StringReader(xsltResource)) ); xmlTransformer.transform( new StreamSource(new StringReader(xmlSourceResource)), new StreamResult(xmlResultResource) ); System.out.println(xmlResultResource.getBuffer().toString()); } } It applies the following hardcoded XSLT transformation: world To the following hardcoded XML document: The result of execution will be hello world == Citations ==