Java tutorial
/* $Id: ExtendedBaseRules.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 java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.HashMap; import java.util.Iterator; import java.util.List; import java.util.Map; /** * <p>Extension of {@link RulesBase} for complex schema.</p> * * <p>This is an extension of the basic pattern matching scheme * intended to improve support for mapping complex xml-schema. * It is intended to be a minimal extension of the standard rules * big enough to support complex schema but without the full generality * offered by more exotic matching pattern rules.</p> * * <h4>When should you use this rather than the original?</h4> * * <p> * This pattern-matching engine is complex and slower than the basic * default RulesBase class, but offers more functionality: * <ul> * <li>Universal patterns allow patterns to be specified which will match * regardless of whether there are "better matching" patterns available.</li> * <li>Parent-match patterns (eg "a/b/?") allow matching for all direct * children of a specified element.</li> * <li>Ancestor-match patterns (eg "a/b/*") allow matching all elements * nested within a specified element to any nesting depth.</li> * <li>Completely-wild patterns ("*" or "!*") allow matching all elements.</li> * </ul> * </p> * * <h4>Universal Match Patterns</h4> * * <p>The default RulesBase pattern-matching engine always attempts to find * the "best matching pattern", and will ignore rules associated with other * patterns that match but are not "as good". As an example, if the pattern * "a/b/c" is associated with rules 1 and 2, and "*/c" is associated with * rules 3 and 4 then element "a/b/c" will cause only rules 1 and 2 to execute. * Rules 3 and 4 do have matching patterns, but because the patterns are shorter * and include wildcard characters they are regarded as being "not as good" as * a direct match. In general, exact patterns are better than wildcard patterns, * and among multiple patterns with wildcards, the longest is preferred. * See the RulesBase class for more information.</p> * * <p>This feature of preferring "better" patterns can be a powerful tool. * However it also means that patterns can interact in unexpected ways.</p> * * <p>When using the ExtendedBaseRules, any pattern prefixed with '!' bypasses * the "best match" feature. Even if there is an exact match or a longer * wildcard match, patterns prefixed by '!' will still be tested to see if * they match, and if so their associated Rule objects will be included in * the set of rules to be executed in the normal manner.</p> * * <ul> * <li>Pattern <code>"!*/a/b"</code> matches whenever an 'b' element * is inside an 'a'.</li> * <li>Pattern <code>"!a/b/?"</code> matches any child of a parent * matching <code>"a/b"</code> (see "Parent Match Patterns").</li> * <li>Pattern <code>"!*/a/b/?"</code> matches any child of a parent * matching <code>"!*/a/b"</code> (see "Parent Match Patterns").</li> * <li>Pattern <code>"!a/b/*"</code> matches any element whose path * starts with "a" then "b" (see "Ancestor Match Patterns").</li> * <li>Pattern <code>"!*/a/b/*"</code> matches any elements whose path * contains 'a/b' (see "Ancestor Match Patterns").</li> * </ul> * * <h4>Parent Match Patterns</h4> * * <p> * These will match direct child elements of a particular parent element. * <ul> * <li> * <code>"a/b/c/?"</code> matches any child whose parent matches * <code>"a/b/c"</code>. Exact parent rules take precedence over Ancestor * Match patterns. * </li> * <li> * <code>"*/a/b/c/?"</code> matches any child whose parent matches * <code>"*/a/b/c"</code>. The longest matching still applies to parent * matches but the length excludes the '?', which effectively means * that standard wildcard matches with the same level of depth are * chosen in preference. * </li> * </ul> * </p> * * <h4>Ancestor Match Patterns</h4> * * <p> * These will match elements whose parentage includes a particular sequence * of elements. * <ul> * <li> * <code>"a/b/*"</code> matches any element whose path starts with * 'a' then 'b'. Exact parent and parent match rules take precedence. * The longest ancestor match will take precedence. * </li> * <li> * <code>"*/a/b/*"</code> matches any elements whose path contains * an element 'a' followed by an element 'b'. The longest matching still * applies but the length excludes the '*' at the end. * </li> * </ul> * </p> * * <h4>Completely Wild Patterns</h4> * * <p>Pattern <code>"*"</code> matches every pattern that isn't matched by * any other basic rule.</p> * * <p>Pattern <code>"!*"</code> matches every pattern.</p> * * <h4>Using The Extended Rules</h4> * * <p>By default, a Digester instance uses a {@link RulesBase} instance as * its pattern matching engine. To use an ExtendedBaseRules instance, call * the Digester.setRules method before adding any Rule objects to the digester * instance: * <pre> * Digester digester = new Digester(); * digester.setRules( new ExtendedBaseRules() ); * </pre></p> * * <p>The most important thing to remember when using the extended rules is * that universal and non-universal patterns are completely independent. * Universal patterns are never affected by the addition of new patterns * or the removal of existing ones. Non-universal patterns are never affected * by the addition of new <em>universal</em> patterns or the removal of * existing <em>universal</em> patterns. As in the basic matching rules, * non-universal (basic) patterns <strong>can</strong> be affected by the * addition of new <em>non-universal</em> patterns or the removal of existing * <em>non-universal</em> patterns, because only rules associated with the * "best matching" pattern for each xml element are executed. * * <p> This means that you can use universal patterns to build up the simple * parts of your structure - for example defining universal creation and * property setting rules. More sophisticated and complex mapping will require * non-universal patterns and this might mean that some of the universal rules * will need to be replaced by a series of special cases using non-universal * rules. But by using universal rules as your backbone, these additions * should not break your existing rules.</p> */ public class ExtendedBaseRules extends RulesBase { // ----------------------------------------------------- Instance Variables /** * Counts the entry number for the rules. */ private int counter = 0; /** * The decision algorithm used (unfortunately) doesn't preserve the entry * order. * This map is used by a comparator which orders the list of matches * before it's returned. * This map stores the entry number keyed by the rule. */ private Map<Rule, Integer> order = new HashMap<Rule, Integer>(); // --------------------------------------------------------- Public Methods /** * Register a new Rule instance matching the specified pattern. * * @param pattern Nesting pattern to be matched for this Rule * @param rule Rule instance to be registered */ @Override public void add(String pattern, Rule rule) { super.add(pattern, rule); counter++; order.put(rule, counter); } /** * Return a List of all registered Rule instances that match the specified * nesting pattern, or a zero-length List if there are no matches. If more * than one Rule instance matches, they <strong>must</strong> be returned * in the order originally registered through the <code>add()</code> * method. * * @param pattern Nesting pattern to be matched */ @Override public List<Rule> match(String namespace, String pattern) { // calculate the pattern of the parent // (if the element has one) String parentPattern = ""; int lastIndex = pattern.lastIndexOf('/'); boolean hasParent = true; if (lastIndex == -1) { // element has no parent hasParent = false; } else { // calculate the pattern of the parent parentPattern = pattern.substring(0, lastIndex); } // we keep the list of universal matches separate List<Rule> universalList = new ArrayList<Rule>(counter); // Universal all wildards ('!*') // These are always matched so always add them List<Rule> tempList = this.cache.get("!*"); if (tempList != null) { universalList.addAll(tempList); } // Universal exact parent match // need to get this now since only wildcards are considered later tempList = this.cache.get("!" + parentPattern + "/?"); if (tempList != null) { universalList.addAll(tempList); } // base behaviour means that if we certain matches, we don't continue // but we just have a single combined loop and so we have to set // a variable boolean ignoreBasicMatches = false; // see if we have an exact basic pattern match List<Rule> rulesList = this.cache.get(pattern); if (rulesList != null) { // we have a match! // so ignore all basic matches from now on ignoreBasicMatches = true; } else { // see if we have an exact child match if (hasParent) { // matching children takes preference rulesList = this.cache.get(parentPattern + "/?"); if (rulesList != null) { // we have a match! // so ignore all basic matches from now on ignoreBasicMatches = true; } else { // we don't have a match yet - so try exact ancester // rulesList = findExactAncesterMatch(pattern); if (rulesList != null) { // we have a match! // so ignore all basic matches from now on ignoreBasicMatches = true; } } } } // OK - we're ready for the big loop! // Unlike the basic rules case, // we have to go through for all those universal rules in all cases. // Find the longest key, ie more discriminant String longKey = ""; int longKeyLength = 0; for (String key : this.cache.keySet()) { // find out if it's a univeral pattern // set a flag boolean isUniversal = key.startsWith("!"); if (isUniversal) { // and find the underlying key key = key.substring(1, key.length()); } // don't need to check exact matches boolean wildcardMatchStart = key.startsWith("*/"); boolean wildcardMatchEnd = key.endsWith("/*"); if (wildcardMatchStart || (isUniversal && wildcardMatchEnd)) { boolean parentMatched = false; boolean basicMatched = false; boolean ancesterMatched = false; boolean parentMatchEnd = key.endsWith("/?"); if (parentMatchEnd) { // try for a parent match parentMatched = parentMatch(key, pattern, parentPattern); } else if (wildcardMatchEnd) { // check for ancester match if (wildcardMatchStart) { String patternBody = key.substring(2, key.length() - 2); if (pattern.endsWith(patternBody)) { ancesterMatched = true; } else { ancesterMatched = (pattern.indexOf(patternBody + "/") > -1); } } else { String bodyPattern = key.substring(0, key.length() - 2); if (pattern.startsWith(bodyPattern)) { if (pattern.length() == bodyPattern.length()) { // exact match ancesterMatched = true; } else { ancesterMatched = (pattern.charAt(bodyPattern.length()) == '/'); } } else { ancesterMatched = false; } } } else { // try for a base match basicMatched = basicMatch(key, pattern); } if (parentMatched || basicMatched || ancesterMatched) { if (isUniversal) { // universal rules go straight in // (no longest matching rule) tempList = this.cache.get("!" + key); if (tempList != null) { universalList.addAll(tempList); } } else { if (!ignoreBasicMatches) { // ensure that all parent matches are SHORTER // than rules with same level of matching. // // the calculations below don't work for universal // matching, but we don't care because in that case // this if-stmt is not entered. int keyLength = key.length(); if (wildcardMatchStart) { --keyLength; } if (wildcardMatchEnd) { --keyLength; } else if (parentMatchEnd) { --keyLength; } if (keyLength > longKeyLength) { rulesList = this.cache.get(key); longKey = key; longKeyLength = keyLength; } } } } } } // '*' works in practice as a default matching // (this is because anything is a deeper match!) if (rulesList == null) { rulesList = this.cache.get("*"); } // if we've matched a basic pattern, then add to the universal list if (rulesList != null) { universalList.addAll(rulesList); } // don't filter if namespace is null if (namespace != null) { // remove invalid namespaces Iterator<Rule> it = universalList.iterator(); while (it.hasNext()) { Rule rule = it.next(); String ns_uri = rule.getNamespaceURI(); if (ns_uri != null && !ns_uri.equals(namespace)) { it.remove(); } } } // need to make sure that the collection is sort in the order // of addition. We use a custom comparator for this Collections.sort(universalList, new Comparator<Rule>() { public int compare(Rule r1, Rule r2) throws ClassCastException { // Get the entry order from the map Integer i1 = order.get(r1); Integer i2 = order.get(r2); // and use that to perform the comparison if (i1 == null) { if (i2 == null) { return 0; } else { return -1; } } else if (i2 == null) { return 1; } return (i1.intValue() - i2.intValue()); } }); return universalList; } /** * Matching parent. */ private boolean parentMatch(String key, String pattern, String parentPattern) { return parentPattern.endsWith(key.substring(1, key.length() - 2)); } /** * Standard match. * Matches the end of the pattern to the key. */ private boolean basicMatch(String key, String pattern) { return (pattern.equals(key.substring(2)) || pattern.endsWith(key.substring(1))); } /** * Finds an exact ancester match for given pattern */ private List<Rule> findExactAncesterMatch(String parentPattern) { List<Rule> matchingRules = null; int lastIndex = parentPattern.length(); while (lastIndex-- > 0) { lastIndex = parentPattern.lastIndexOf('/', lastIndex); if (lastIndex > 0) { matchingRules = this.cache.get(parentPattern.substring(0, lastIndex) + "/*"); if (matchingRules != null) { return matchingRules; } } } return null; } }