Commons Digester example source code file (Main.java)

This example Commons Digester source code file (Main.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Digester tags/keywords

addressbook, addressbook, digester, digester, exception, exception, main, net, network, sax, string, string, url

The Commons Digester Main.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */ 

import org.apache.commons.digester.Digester;
import org.apache.commons.digester.xmlrules.DigesterLoader;
import org.xml.sax.InputSource;
import java.net.URL;

/**
 * A simple program to demonstrate the basic functionality of the
 * Commons Digester module with the xmlrules extension.
 * <p>
 * This code will parse the provided "example.xml" file to build a tree
 * of java objects, then cause those objects to print out their values
 * to demonstrate that the input file has been processed correctly.
 * <p>
 * Unlike the "addressbook" example in the "api" section, this implementation
 * has no parsing rules hard-wired into the code in this class. Instead, the
 * parsing rules are loaded from an external file at runtime. This allows
 * the parsing rules to be modified without compiling the code, and 
 * potentially makes it somewhat easier to review the parsing rules.
 * <p>
 * Note, however, that there is tyically quite a tight coupling between
 * the parsing rules and the <i>purpose of the application which means
 * that it may not be all that common for parsing rules to be altered
 * without the application code also being altered, so only in some cases
 * will this prove of benefit. As with all software, it must be determined
 * whether this feature provides a true benefit in the context of the 
 * application it is being applied to.
 * <p>
 * Usage: java Main xmlrules.xml example.xml
 */
public class Main {
    
    /**
     * Main method : entry point for running this example program.
     * <p>
     * Usage: java Example example.xml
     */
    public static void main(String[] args) throws Exception {
        if (args.length != 2) {
            usage();
            System.exit(-1);
        }
        
        String rulesfileName = args[0];
        String datafileName = args[1];
        
        // Create a Digester instance which has been initialised with
        // rules loaded from the specified file.
        URL rulesURL = ClassLoader.getSystemResource(rulesfileName);
        if (rulesURL == null) {
            System.out.println("Unable to find rules file.");
            System.exit(-1);
        }
        Digester d = DigesterLoader.createDigester(rulesURL);
        
        // Prime the digester stack with an object for rules to
        // operate on. Note that it is quite common for "this"
        // to be the object pushed.
        AddressBook book = new AddressBook();
        d.push(book);
        
        // Process the input file.
        try {
            java.io.File srcfile = new java.io.File(datafileName);
            d.parse(srcfile);
        }
        catch(java.io.IOException ioe) {
            System.out.println("Error reading input file:" + ioe.getMessage());
            System.exit(-1);
        }
        catch(org.xml.sax.SAXException se) {
            System.out.println("Error parsing input file:" + se.getMessage());
            System.exit(-1);
        }
        
        
        // Print out all the contents of the address book, as loaded from
        // the input file.
        book.print();
    }
    
    private static void usage() {
        System.out.println("Usage: java Main xmlrules.xml example.xml");
    }
}