Commons Digester example source code file (SimpleRegexMatcher.java)

This example Commons Digester source code file (SimpleRegexMatcher.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

base, base, camparing, log, log, no, override, regex, regex, regexmatcher, searching, string, string, trying

The Commons Digester SimpleRegexMatcher.java source code

/* $Id: SimpleRegexMatcher.java 992060 2010-09-02 19:09:47Z simonetripodi $
 *
 * 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.
 */

package org.apache.commons.digester;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * <p>Simple regex pattern matching algorithm.

 * 
 * <p>This uses just two wildcards:
 * <ul>
 *  <li>* matches any sequence of none, one or more characters
 *  <li>? matches any one character 
 * </ul>
 * Escaping these wildcards is not supported .</p>
 *
 * @since 1.5
 */

public class SimpleRegexMatcher extends RegexMatcher {
    
    // --------------------------------------------------------- Fields
    
    /** Default log (class wide) */
    private static final Log baseLog = LogFactory.getLog(SimpleRegexMatcher.class);
    
    /** Custom log (can be set per object) */
    private Log log = baseLog;
    
    // --------------------------------------------------------- Properties
    
    /** 
     * Gets the <code>Log implementation.
     */
    public Log getLog() {
        return log;
    }
    
    /**
     * Sets the current <code>Log implementation used by this class.
     */
    public void setLog(Log log) {
        this.log = log;
    }
    
    // --------------------------------------------------------- Public Methods
    
    /** 
     * Matches using simple regex algorithm.
     * 
     *
     * @param basePattern the standard digester path representing the element
     * @param regexPattern the regex pattern the path will be tested against
     * @return true if the given pattern matches the given path
     */
    @Override
    public boolean match(String basePattern, String regexPattern) {
        // check for nulls
        if (basePattern == null || regexPattern == null) {
            return false;
        }
        return match(basePattern, regexPattern, 0, 0);
    }
    
    // --------------------------------------------------------- Implementations Methods
    
    /**
     * Implementation of regex matching algorithm.
     * This calls itself recursively.
     */
    private boolean match(String basePattern, String regexPattern, int baseAt, int regexAt) {
        if (log.isTraceEnabled()) {
            log.trace("Base: " + basePattern);
            log.trace("Regex: " + regexPattern);
            log.trace("Base@" + baseAt);
            log.trace("Regex@" + regexAt);
        }
        
        // check bounds
        if (regexAt >= regexPattern.length()) {
            // maybe we've got a match
            if (baseAt >= basePattern.length()) {
                // ok!
                return true;
            }
            // run out early
            return false;
            
        } else {
            if (baseAt >= basePattern.length()) {
                // run out early
                return false;
            }
        }
        
        // ok both within bounds
        char regexCurrent = regexPattern.charAt(regexAt);
        switch (regexCurrent) {
            case '*':
                // this is the tricky case
                // check for terminal 
                if (++regexAt >= regexPattern.length()) {
                    // this matches anything let - so return true
                    return true;
                }
                // go through every subsequent apperance of the next character
                // and so if the rest of the regex matches
                char nextRegex = regexPattern.charAt(regexAt);
                if (log.isTraceEnabled()) {
                    log.trace("Searching for next '" + nextRegex + "' char");
                }
                int nextMatch = basePattern.indexOf(nextRegex, baseAt);
                while (nextMatch != -1) {
                    if (log.isTraceEnabled()) {
                        log.trace("Trying '*' match@" + nextMatch);
                    }
                    if (match(basePattern, regexPattern, nextMatch, regexAt)) {
                        return true;
                    }
                    nextMatch = basePattern.indexOf(nextRegex, nextMatch + 1);
                }
                log.trace("No matches found.");
                return false;
                
            case '?':
                // this matches anything
                return match(basePattern, regexPattern, ++baseAt, ++regexAt);
            
            default:
                if (log.isTraceEnabled()) {
                    log.trace("Camparing " + regexCurrent + " to " + basePattern.charAt(baseAt));
                }
                if (regexCurrent == basePattern.charAt(baseAt)) {
                    // still got more to go
                    return match(basePattern, regexPattern, ++baseAt, ++regexAt);
                }
                return false;
        }
    }
}