Class Inversion

  • public class Inversion
    extends java.lang.Object
    This class represents an expression that has been "inverted" (in the Jackson sense) so that its execution is push-driven, that is, driven by events from the streamed document. The route taken by these events through the expressions in the expression tree is the "streaming route". Currently this class is simply a wrapper around the Inversion object that represents the path through the expression tree containing expressions that are evaluated in push mode, that is, those that perform downward navigation in the streamed document input.

    The expression inversion is represented by a "streaming route", which is the path of nodes in the expression tree, from the root to a leaf, being evaluated in streaming mode. The streaming route starts with a Watch, which is notified by the parser of interesting events. It then proceeds through a series of Feeds which process these events (or items composed from these events) before finally being output to a Receiver which handles the transformation result.

    The list of actions is "outermost expression first". This is the opposite of the order in which the events actually pass through the pipeline.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static class  Inversion.PushAction
      A PushAction is a collection of data that together represents the strategy for how an expression should be evaluated in push mode.
    • Constructor Summary

      Constructor Description
    • Constructor Detail

      • Inversion

        public Inversion()
    • Method Detail

      • invertExpression

        public static Inversion invertExpression​(Expression exp,
                                                 boolean forGrouping)
                                          throws XPathException
        Compute the Jackson inversion of an expression. The effect is (a) to determine whether the expression is streamable (throwing an exception if not), and (b) to construct the "Streaming route", that is, the path through the expression tree containing expressions that perform downward navigation within the streamed document
        exp - the expression to be inverted
        forGrouping - true if the expression is the body of a for-each-group that is to be inverted with respect to the grouping variable rather than the context item
        the inverted expression
        XPathException - if the expression is not streamable
      • copy

        public Inversion copy()
        Create a copy of this inverted expression
        the copy
      • append

        public void append​(Inversion.PushAction action)
        Add an action to the end of the streaming route (a subexpression of the currently-last expression, which is therefore first to receive events from the parser)
        action - the action to be appended
      • prepend

        public void prepend​(Inversion.PushAction action)
        Add an action to the start of this streaming route (a parent of the currently-first expression, which is therefore last to receive events from the parser)
        action - the action to be prepended
      • getRoute

        public java.util.List<Inversion.PushAction> getRoute()
        Get the list of push actions making up the streaming route
        the list of push actions
      • getWatch

        public Trigger getWatch​(WatchManager watchManager,
                                ItemFeed parentFeed,
                                XPathContext context)
                         throws XPathException
        Make a Watch to represent this streaming route. The Watch is registered with the WatchManager so it can be notified of events that cause it to be activated
        watchManager - the WatchManager (which is known to each Watch under its control)
        parentFeed - Maybe null. The destination of events after processing by this Watch
        context - XPath context object
        the Watch
        XPathException - if an error occurs, e.g. if streaming is not possible.
      • explain

        public void explain​(ExpressionPresenter out)
        Display the streaming route for diagnostic purposes
        out - the display destination