Parse a web.xml file using the SAX2 API : Web INF XML « Servlets « Java
Parse a web.xml file using the SAX2 API
/*
* 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.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;
/**
* Parse a web.xml file using the SAX2 API. This class extends DefaultHandler so
* that instances can serve as SAX2 event handlers, and can be notified by the
* parser of parsing events. We simply override the methods that receive events
* we're interested in
*/
public class ListServlets extends org.xml.sax.helpers.DefaultHandler {
/** The main method sets things up for parsing */
public static void main(String[] args) throws IOException, SAXException,
ParserConfigurationException {
// We use a SAXParserFactory to obtain a SAXParser, which
// encapsulates a SAXReader.
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(false); // We don't want validation
factory.setNamespaceAware(false); // No namespaces please
// Create a SAXParser object from the factory
SAXParser parser = factory.newSAXParser();
// Now parse the file specified on the command line using
// an instance of this class to handle the parser callbacks
parser.parse(new File(args[0]), new ListServlets());
}
HashMap nameToClass; // Map from servlet name to servlet class name
HashMap nameToID; // Map from servlet name to id attribute
HashMap nameToPatterns; // Map from servlet name to url patterns
StringBuffer accumulator; // Accumulate text
String servletName, servletClass, servletPattern; // Remember text
String servletID; // Value of id attribute of <servlet> tag
// Called at the beginning of parsing. We use it as an init() method
public void startDocument() {
accumulator = new StringBuffer();
nameToClass = new HashMap();
nameToID = new HashMap();
nameToPatterns = new HashMap();
}
// When the parser encounters plain text (not XML elements), it calls
// this method, which accumulates them in a string buffer.
// Note that this method may be called multiple times, even with no
// intervening elements.
public void characters(char[] buffer, int start, int length) {
accumulator.append(buffer, start, length);
}
// At the beginning of each new element, erase any accumulated text.
public void startElement(String namespaceURL, String localName, String qname,
Attributes attributes) {
accumulator.setLength(0);
// If its a servlet tag, look for id attribute
if (qname.equals("servlet"))
servletID = attributes.getValue("id");
}
// Take special action when we reach the end of selected elements.
// Although we don't use a validating parser, this method does assume
// that the web.xml file we're parsing is valid.
public void endElement(String namespaceURL, String localName, String qname) {
// Since we've indicated that we don't want name-space aware
// parsing, the element name is in qname. If we were doing
// namespaces, then qname would include the name, colon and prefix,
// and localName would be the name without the the prefix or colon.
if (qname.equals("servlet-name")) { // Store servlet name
servletName = accumulator.toString().trim();
} else if (qname.equals("servlet-class")) { // Store servlet class
servletClass = accumulator.toString().trim();
} else if (qname.equals("url-pattern")) { // Store servlet pattern
servletPattern = accumulator.toString().trim();
} else if (qname.equals("servlet")) { // Map name to class
nameToClass.put(servletName, servletClass);
nameToID.put(servletName, servletID);
} else if (qname.equals("servlet-mapping")) {// Map name to pattern
List patterns = (List) nameToPatterns.get(servletName);
if (patterns == null) {
patterns = new ArrayList();
nameToPatterns.put(servletName, patterns);
}
patterns.add(servletPattern);
}
}
// Called at the end of parsing. Used here to print our results.
public void endDocument() {
// Note the powerful uses of the Collections framework. In two lines
// we get the key objects of a Map as a Set, convert them to a List,
// and sort that List alphabetically.
List servletNames = new ArrayList(nameToClass.keySet());
Collections.sort(servletNames);
// Loop through servlet names
for (Iterator iterator = servletNames.iterator(); iterator.hasNext();) {
String name = (String) iterator.next();
// For each name get class and URL patterns and print them.
String classname = (String) nameToClass.get(name);
String id = (String) nameToID.get(name);
List patterns = (List) nameToPatterns.get(name);
System.out.println("Servlet: " + name);
System.out.println("Class: " + classname);
if (id != null)
System.out.println("ID: " + id);
if (patterns != null) {
System.out.println("Patterns:");
for (Iterator i = patterns.iterator(); i.hasNext();) {
System.out.println("\t" + i.next());
}
}
System.out.println();
}
}
// Issue a warning
public void warning(SAXParseException exception) {
System.err
.println("WARNING: line " + exception.getLineNumber() + ": " + exception.getMessage());
}
// Report a parsing error
public void error(SAXParseException exception) {
System.err.println("ERROR: line " + exception.getLineNumber() + ": " + exception.getMessage());
}
// Report a non-recoverable error and exit
public void fatalError(SAXParseException exception) throws SAXException {
System.err.println("FATAL: line " + exception.getLineNumber() + ": " + exception.getMessage());
throw (exception);
}
}
