jena-arq/src/main/java/org/apache/jena/sparql/syntax/ElementWalker.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.sparql.syntax;


/** An element visitor that walks the graph pattern tree for one query level. 
 *  applying a visitor at each Element traversed.<br/>
 *  Does not process subqueries.<br/>      
 *  Does not process (NOT)EXISTS in filters.<br/>
 *  These will need to call down themselves if it is meaningful for the visitor.
 *  Bottom-up walk - apply to subelements before applying to current element.
 */

public class ElementWalker 
{
    public static void walk(Element el, ElementVisitor visitor)
    {
        walk(el, visitor, null, null) ;
    }
    
    public static void walk(Element el, ElementVisitor visitor, ElementVisitor beforeVisitor, ElementVisitor afterVisitor)
    {
        EltWalker w = new EltWalker(visitor, beforeVisitor, afterVisitor) ;
        el.visit(w) ;
    }

    protected static void walk$(Element el, EltWalker walker)
    {
        el.visit(walker) ;
    }

    static class EltWalker implements ElementVisitor
    {
        protected final ElementVisitor proc ;
        protected final ElementVisitor beforeVisitor ;
        protected final ElementVisitor afterVisitor ;

        protected EltWalker(ElementVisitor visitor, ElementVisitor beforeVisitor, ElementVisitor afterVisitor)
        { 
            proc = visitor ;
            this.beforeVisitor= beforeVisitor ; 
            this.afterVisitor = afterVisitor ;
        }

        private void before(Element elt)
        {
            if ( beforeVisitor != null )
                elt.visit(beforeVisitor) ;
        }

        private void after(Element elt)
        {
            if ( afterVisitor != null )
                elt.visit(afterVisitor) ;
        }

        @Override
        public void visit(ElementTriplesBlock el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementFilter el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementAssign el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementBind el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementFind el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }
        

        @Override
        public void visit(ElementData el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementUnion el)
        {
            before(el) ;
            for ( Element e : el.getElements() )
                e.visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementGroup el)
        {
            before(el) ;
            for (Element e : el.getElements())
                e.visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementOptional el)
        {
            before(el) ;
            if ( el.getOptionalElement() != null )
                el.getOptionalElement().visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementDataset el)
        {
            before(el) ;
            if ( el.getElement() != null )
                el.getElement().visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementNamedGraph el)
        {
            before(el) ;
            if ( el.getElement() != null )
                el.getElement().visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementService el)
        {
            before(el) ;
            if ( el.getElement() != null )
                el.getElement().visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        // EXISTs, NOT EXISTs also occur in FILTERs via expressions.
        
        @Override
        public void visit(ElementExists el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementNotExists el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementMinus el)
        {
            before(el) ;
            if ( el.getMinusElement() != null )
                el.getMinusElement().visit(this) ;
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementSubQuery el)
        {
            before(el) ;
            // This does not automatically walk into the subquery.
            proc.visit(el) ;
            after(el) ;
        }

        @Override
        public void visit(ElementPathBlock el)
        {
            before(el) ;
            proc.visit(el) ;
            after(el) ;
        }
    }
}