Package org.geotools.filter

Class LogicSAXParser

  • public class LogicSAXParser
extends Object
    Processes messages from clients to create Logic Filters. Handles nested logic filters. Filters should call start and end when they reach logic filters, and create when the filter is complete.

    This documenation provided by Dave Blasby April 1/2005 after fixing GEOS-328: DJB: okay, there's no where near enough comments in here to understand whats going on. Hopefully I'm correct. I've looked at this for a bit, and this is what I can figure out.

    This is called by the FilterFilter class (nice name...NOT) which is also a sax parser-like class. Basically, the FilterFilter does most of the Filter parsing - but it hands most of the work off to the appropriate classes. For NOT, AND, OR clauses, this class is used.

    As a simple example, [STATE_NAME = 'NY'] [STATE_NAME = 'WA'] Or, in long form: STATE_NAME NY STATE_NAME WA

    The "PropertyIsEqualTo" is handled by another parser, so we dont have to worry about it here for the moment.

    So, the order of events are like this:

    start( "OR" ) add([STATE_NAME = 'NY']) // these are handled by another class add([STATE_NAME = 'WA']) // these are handled by another class end ("OR") create() // this creates an actual Filter [[ STATE_NAME = NY ] OR [ STATE_NAME = WA ]]

    This is pretty simple, but it gets more complex when you have nested structures.

    STATE_NAME NY STATE_NAME WA STATE_NAME BC

    Again, we're going to ignore the "PropertyIsEqualTo" stuff since its handled elsewhere.

    The main idea is that there will be a LogicSAXParser for the top-level "AND" and another one for the nested "OR". It gets a bit harder to describe because the classes start passing events to each other.

    start("AND") -- the parent LogicSAXParser starts to construct an "AND" filter start("OR") -- the "AND" parser sees that its sub-element is another logic operator. It makes another LogicSAXParser that will handle the "OR" SAX events. add([STATE_NAME = 'NY']) -- this is sent to the "AND" parser. It then sends it to the "OR" parser. + "OR" parser remembers this component add([STATE_NAME = 'WA']) -- this is sent to the "AND" parser. It then sends it to the "OR" parser. + "OR" parser remembers this component end("OR") -- this is sent to the "AND" parser. It then sends it to the "OR" parser. + The "OR" parser marks itself as complete + The "AND" parser notices that its child is completed parsing + The "AND" parser calls create() on the "OR" parser to make a filter (see next step) + Since "OR" is finished, "AND" stop passing events to it. "OR".create() -- makes a "[[ STATE_NAME = NY ] OR [ STATE_NAME = WA ]]" and "AND" remembers it as a component add ([ STATE_NAME = BC ]) --This is added as a component to the "AND" filter. end ("AND") -- the "AND" parser marks itself as complete create() -- the "AND" parser creates a FILTER [[[ STATE_NAME = NY ] OR [ STATE_NAME = WA ]] AND [ STATE_NAME = BC ]]

    Higher levels of nesting work the same way - each level will send the event down to the next level.

    If logicFilter == null then this object is the one doing the processing. If its non-null, then the sub-object is doing the processing - event are sent to it.

    Author:
    Rob Hranac, Vision for New York, Chris Holmes, TOPP

    • Constructor Detail

      • LogicSAXParser

        public LogicSAXParser()
        Constructor which flags the operator as between.

      • LogicSAXParser

        public LogicSAXParser​(FilterFactory factory)
        Constructor injection

    • Method Detail

      • setFilterFactory

        public void setFilterFactory​(FilterFactory factory)
        Setter injection

      • start

        public void start​(short logicType)
           throws IllegalFilterException
        To be called by a parser to start the creation of a logic filter. Can start a nested or a base logic filter.
        Parameters:
        logicType - OR, or AND abstract filter type.
        Throws:
        IllegalFilterException - if filter type does not match declared type.

      • end

        public void end​(short logicType)
         throws IllegalFilterException
        To be called when the sax parser reaches the end of a logic filter. Tells this class to complete.
        Parameters:
        logicType - the Filter type.
        Throws:
        IllegalFilterException - If the end message can't be processed in this state.

      • add

        public void add​(Filter filter)
        Adds a filter to the current logic list.
        Parameters:
        filter - The filter to be added.

      • isComplete

        public boolean isComplete()
        indicates if the logic filter is complete.
        Returns:
        true if this holds a complete logic filter to be created, false otherwise.