Class CurrentGroupPattern

All Implemented Interfaces:
ExportAgent, Locatable, IdentityComparable, Traceable

public class CurrentGroupPattern extends AnchorPattern
This is a special pattern that matches the "anchor node". It is used for the selectors that arise when evaluating XPath expressions in streaming mode; the anchor node is the context node for the streamed XPath evaluation. Given a streamed evaluation of an expression such as ./BOOKS/BOOK/PRICE, the way we evaluate this is to turn it into a pattern, which is then tested against all descendant nodes. Conceptually the pattern is $A/BOOKS/BOOK/PRICE, where $A is referred to as the anchor node. When we evaluate the pattern against (say) a PRICE element, the match will only succeed if the name of the element is "PRICE" and its ancestors are, in order, a BOOK element, a BOOKS element, and the anchor node $A.
  • Constructor Details

    • CurrentGroupPattern

      protected CurrentGroupPattern()
  • Method Details

    • getInstance

      public static CurrentGroupPattern getInstance()
    • matchesCurrentGroup

      public boolean matchesCurrentGroup()
      Ask whether the pattern is anchored on a call on current-group()
      Overrides:
      matchesCurrentGroup in class Pattern
      Returns:
      true if calls on matchesBeneathAnchor should test with all nodes in the current group as anchor nodes. If false, only the first node in a group is treated as the anchor node
    • matchesBeneathAnchor

      public boolean matchesBeneathAnchor(NodeInfo node, NodeInfo anchor, XPathContext context) throws XPathException
      Description copied from class: AnchorPattern
      Determine whether this pattern matches a given Node within the subtree rooted at a given anchor node. This method is used when the pattern is used for streaming.
      Overrides:
      matchesBeneathAnchor in class AnchorPattern
      Parameters:
      node - The NodeInfo representing the Element or other node to be tested against the Pattern
      anchor - The anchor node, which must match any AnchorPattern subpattern
      context - The dynamic context. Only relevant if the pattern uses variables, or contains calls on functions such as document() or key().
      Returns:
      true if the node matches the Pattern, false otherwise
      Throws:
      XPathException - if an error occurs while matching the pattern (the caller will usually treat this the same as a false result)
    • export

      public void export(ExpressionPresenter presenter) throws XPathException
      Description copied from class: Expression
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      export in interface ExportAgent
      Overrides:
      export in class AnchorPattern
      Parameters:
      presenter - the expression presenter used to display the structure
      Throws:
      XPathException - if the export fails, for example if an expression is found that won't work in the target environment.