Class 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 
      Modifier and Type Field Description
      private int counter
      Counts the entry number for the rules.
      private java.util.Map order
      The decision algorithm used (unfortunately) doesn't preserve the entry order.
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void add​(java.lang.String pattern, Rule rule)
      Register a new Rule instance matching the specified pattern.
      private boolean basicMatch​(java.lang.String key, java.lang.String pattern)
      Standard match.
      private java.util.List findExactAncesterMatch​(java.lang.String parentPattern)
      Finds an exact ancester match for given pattern
      java.util.List match​(java.lang.String namespace, java.lang.String pattern)
      Return a List of all registered Rule instances that match the specified nesting pattern, or a zero-length List if there are no matches.
      private boolean parentMatch​(java.lang.String key, java.lang.String pattern, java.lang.String parentPattern)
      Matching parent.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • counter

        private int counter
        Counts the entry number for the rules.
      • order

        private java.util.Map order
        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.
    • Constructor Detail

      • ExtendedBaseRules

        public ExtendedBaseRules()
    • Method Detail

      • add

        public void add​(java.lang.String pattern,
                        Rule rule)
        Register a new Rule instance matching the specified pattern.
        Specified by:
        add in interface Rules
        Overrides:
        add in class RulesBase
        Parameters:
        pattern - Nesting pattern to be matched for this Rule
        rule - Rule instance to be registered
      • match

        public java.util.List match​(java.lang.String namespace,
                                    java.lang.String pattern)
        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:
        pattern - Nesting pattern to be matched
        namespace - Namespace URI for which to select matching rules, or null to match regardless of namespace URI
      • parentMatch

        private boolean parentMatch​(java.lang.String key,
                                    java.lang.String pattern,
                                    java.lang.String parentPattern)
        Matching parent.
      • basicMatch

        private boolean basicMatch​(java.lang.String key,
                                   java.lang.String pattern)
        Standard match. Matches the end of the pattern to the key.
      • findExactAncesterMatch

        private java.util.List findExactAncesterMatch​(java.lang.String parentPattern)
        Finds an exact ancester match for given pattern