org.apache.commons.digester3
Class ExtendedBaseRules

java.lang.Object
  org.apache.commons.digester3.AbstractRulesImpl
      org.apache.commons.digester3.RulesBase
          org.apache.commons.digester3.ExtendedBaseRules

All Implemented Interfaces:

Rules

public class ExtendedBaseRules
extends RulesBase

Extension of RulesBase for complex schema.

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.

When should you use this rather than the original?

This pattern-matching engine is complex and slower than the basic default RulesBase class, but offers more functionality:

• Universal patterns allow patterns to be specified which will match regardless of whether there are "better matching" patterns available.
• Parent-match patterns (eg "a/b/?") allow matching for all direct children of a specified element.
• Ancestor-match patterns (eg "a/b/*") allow matching all elements nested within a specified element to any nesting depth.
• Completely-wild patterns ("*" or "!*") allow matching all elements.

Universal Match Patterns

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.

This feature of preferring "better" patterns can be a powerful tool. However it also means that patterns can interact in unexpected ways.

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.

• Pattern "!*/a/b" matches whenever an 'b' element is inside an 'a'.
• Pattern "!a/b/?" matches any child of a parent matching "a/b" (see "Parent Match Patterns").
• Pattern "!*/a/b/?" matches any child of a parent matching "!*/a/b" (see "Parent Match Patterns").
• Pattern "!a/b/*" matches any element whose path starts with "a" then "b" (see "Ancestor Match Patterns").
• Pattern "!*/a/b/*" matches any elements whose path contains 'a/b' (see "Ancestor Match Patterns").

Parent Match Patterns

These will match direct child elements of a particular parent element.

• "a/b/c/?" matches any child whose parent matches "a/b/c". Exact parent rules take precedence over Ancestor Match patterns.
• "*/a/b/c/?" matches any child whose parent matches "*/a/b/c". 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.

Ancestor Match Patterns

These will match elements whose parentage includes a particular sequence of elements.

• "a/b/*" 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.
• "*/a/b/*" 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.

Completely Wild Patterns

Pattern "*" matches every pattern that isn't matched by any other basic rule.

Pattern "!*" matches every pattern.

Using The Extended Rules

By default, a Digester instance uses a 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:

 Digester digester = new Digester();
 digester.setRules( new ExtendedBaseRules() );
 

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 universal patterns or the removal of existing universal patterns. As in the basic matching rules, non-universal (basic) patterns can be affected by the addition of new non-universal patterns or the removal of existing non-universal patterns, because only rules associated with the "best matching" pattern for each xml element are executed.

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.

Field Summary

Fields inherited from class org.apache.commons.digester3.RulesBase

cache, rules

Constructor Summary

ExtendedBaseRules()

Method Summary

List<Rule>	match(String namespaceURI, String pattern, String name, Attributes attributes) Return a List of all registered Rule instances that match the specified nesting pattern, or a zero-length List if there are no matches.
protected void	registerRule(String pattern, Rule rule) Register rule at given pattern.

Methods inherited from class org.apache.commons.digester3.RulesBase

clear, lookup, rules, setDigester

Methods inherited from class org.apache.commons.digester3.AbstractRulesImpl

add, getDigester, getNamespaceURI, setNamespaceURI

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExtendedBaseRules

public ExtendedBaseRules()

Method Detail

registerRule

protected void registerRule(String pattern,
                            Rule rule)

Register rule at given pattern. The the Digester and namespaceURI properties of the given Rule can be assumed to have been set properly before this method is called.

Overrides:

registerRule in class RulesBase

Parameters:

pattern - Nesting pattern to be matched for this Rule

rule - Rule instance to be registered

match

public List<Rule> match(String namespaceURI,
                        String pattern,
                        String name,
                        Attributes attributes)

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 must be returned in the order originally registered through the add() method.

Specified by:

match in interface Rules

Overrides:

match in class RulesBase

Parameters:

namespaceURI - Namespace URI for which to select matching rules, or null to match regardless of namespace URI

pattern - Nesting pattern to be matched

name - the local name if the parser is namespace aware, or just the element name otherwise

attributes - The attribute list of the current matching element

Returns:

a List of all registered Rule instances that match the specified nesting pattern