A WebAppConfig object is a wrapper around a DOM tree for a web.xml file
/*
* Copyright (c) 2004 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 3nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose,
* including teaching and use in open-source projects.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book,
* please visit http://www.davidflanagan.com/javaexamples3.
*/
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.w3c.dom.Text;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
/**
* A WebAppConfig object is a wrapper around a DOM tree for a web.xml file. The
* methods of the class use the DOM API to work with the tree in various ways.
*/
public class WebAppConfig {
/** The main method creates and demonstrates a WebAppConfig object */
public static void main(String[] args) throws IOException, SAXException,
ParserConfigurationException, TransformerConfigurationException, TransformerException {
// Create a new WebAppConfig object that represents the web.xml
// file specified by the first command-line argument
WebAppConfig config = new WebAppConfig(new File(args[0]));
// Query the tree for the class name associated with the specified
// servlet name
System.out.println("Class for servlet " + args[1] + " is " + config.getServletClass(args[1]));
// Add a new servlet name-to-class mapping to the DOM tree
config.addServlet("foo", "bar");
// And write out an XML version of the DOM tree to standard out
config.output(new PrintWriter(System.out));
}
org.w3c.dom.Document document; // This field holds the parsed DOM tree
/**
* This constructor method is passed an XML file. It uses the JAXP API to
* obtain a DOM parser, and to parse the file into a DOM Document object,
* which is used by the remaining methods of the class.
*/
public WebAppConfig(File configfile) throws IOException, SAXException,
ParserConfigurationException {
// Get a JAXP parser factory object
javax.xml.parsers.DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
// Tell the factory what kind of parser we want
dbf.setValidating(false);
// Use the factory to get a JAXP parser object
javax.xml.parsers.DocumentBuilder parser = dbf.newDocumentBuilder();
// Tell the parser how to handle errors. Note that in the JAXP API,
// DOM parsers rely on the SAX API for error handling
parser.setErrorHandler(new org.xml.sax.ErrorHandler() {
public void warning(SAXParseException e) {
System.err.println("WARNING: " + e.getMessage());
}
public void error(SAXParseException e) {
System.err.println("ERROR: " + e.getMessage());
}
public void fatalError(SAXParseException e) throws SAXException {
System.err.println("FATAL: " + e.getMessage());
throw e; // re-throw the error
}
});
// Finally, use the JAXP parser to parse the file. This call returns
// A Document object. Now that we have this object, the rest of this
// class uses the DOM API to work with it; JAXP is no longer required.
document = parser.parse(configfile);
}
/**
* This method looks for specific Element nodes in the DOM tree in order to
* figure out the classname associated with the specified servlet name
*/
public String getServletClass(String servletName) {
// Find all <servlet> elements and loop through them.
NodeList servletnodes = document.getElementsByTagName("servlet");
int numservlets = servletnodes.getLength();
for (int i = 0; i < numservlets; i++) {
Element servletTag = (Element) servletnodes.item(i);
// Get the first <servlet-name> tag within the <servlet> tag
Element nameTag = (Element) servletTag.getElementsByTagName("servlet-name").item(0);
if (nameTag == null)
continue;
// The <servlet-name> tag should have a single child of type
// Text. Get that child, and extract its text. Use trim()
// to strip whitespace from the beginning and end of it.
String name = ((Text) nameTag.getFirstChild()).getData().trim();
// If this <servlet-name> tag has the right name
if (servletName.equals(name)) {
// Get the matching <servlet-class> tag
Element classTag = (Element) servletTag.getElementsByTagName("servlet-class").item(0);
if (classTag != null) {
// Extract the tag's text as above, and return it
Text classTagContent = (Text) classTag.getFirstChild();
return classTagContent.getNodeValue().trim();
}
}
}
// If we get here, no matching servlet name was found
return null;
}
/**
* This method adds a new name-to-class mapping in in the form of a <servlet>
* sub-tree to the document.
*/
public void addServlet(String servletName, String className) {
// Create the <servlet> tag
Element newNode = document.createElement("servlet");
// Create the <servlet-name> and <servlet-class> tags
Element nameNode = document.createElement("servlet-name");
Element classNode = document.createElement("servlet-class");
// Add the name and classname text to those tags
nameNode.appendChild(document.createTextNode(servletName));
classNode.appendChild(document.createTextNode(className));
// And add those tags to the servlet tag
newNode.appendChild(nameNode);
newNode.appendChild(classNode);
// Now that we've created the new sub-tree, figure out where to put
// it. This code looks for another servlet tag and inserts the new
// one right before it. Note that this code will fail if the document
// does not already contain at least one <servlet> tag.
NodeList servletnodes = document.getElementsByTagName("servlet");
Element firstServlet = (Element) servletnodes.item(0);
// Insert the new node before the first servlet node
firstServlet.getParentNode().insertBefore(newNode, firstServlet);
}
/**
* Output the DOM tree to the specified stream as an XML document. See the
* XMLDocumentWriter example for the details.
*/
public void output(PrintWriter out) throws TransformerConfigurationException,
TransformerException {
TransformerFactory factory = TransformerFactory.newInstance();
Transformer transformer = factory.newTransformer();
transformer.transform(new javax.xml.transform.dom.DOMSource(document),
new javax.xml.transform.stream.StreamResult(out));
}
}
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