Commons JXPath example source code file (Path.java)

This example Commons JXPath source code file (Path.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons JXPath tags/keywords

childcontext, descendantcontext, evalcontext, evalcontext, nodenametest, nodenametest, nodepointer, nodepointer, nodetest, nodetypetest, pointer, pointer, step, string

The Commons JXPath Path.java source code

/*
 * 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.commons.jxpath.ri.compiler;

import org.apache.commons.jxpath.Pointer;
import org.apache.commons.jxpath.ri.Compiler;
import org.apache.commons.jxpath.ri.EvalContext;
import org.apache.commons.jxpath.ri.QName;
import org.apache.commons.jxpath.ri.axes.AncestorContext;
import org.apache.commons.jxpath.ri.axes.AttributeContext;
import org.apache.commons.jxpath.ri.axes.ChildContext;
import org.apache.commons.jxpath.ri.axes.DescendantContext;
import org.apache.commons.jxpath.ri.axes.InitialContext;
import org.apache.commons.jxpath.ri.axes.NamespaceContext;
import org.apache.commons.jxpath.ri.axes.ParentContext;
import org.apache.commons.jxpath.ri.axes.PrecedingOrFollowingContext;
import org.apache.commons.jxpath.ri.axes.PredicateContext;
import org.apache.commons.jxpath.ri.axes.SelfContext;
import org.apache.commons.jxpath.ri.axes.SimplePathInterpreter;
import org.apache.commons.jxpath.ri.axes.UnionContext;
import org.apache.commons.jxpath.ri.model.NodePointer;

/**
 * @author Dmitri Plotnikov
 * @version $Revision: 681111 $ $Date: 2008-07-30 11:30:29 -0500 (Wed, 30 Jul 2008) $
 */
public abstract class Path extends Expression {

    private Step[] steps;
    private boolean basicKnown = false;
    private boolean basic;

    /**
     * Create a new Path.
     * @param steps that compose the Path
     */
    public Path(Step[] steps) {
        this.steps = steps;
    }

    /**
     * Get the steps.
     * @return Step[]
     */
    public Step[] getSteps() {
        return steps;
    }

    public boolean computeContextDependent() {
        if (steps != null) {
            for (int i = 0; i < steps.length; i++) {
                if (steps[i].isContextDependent()) {
                    return true;
                }
            }
        }
        return false;
    }

    /**
     * Recognizes paths formatted as <code>foo/bar[3]/baz[@name = 'biz'].
     * The evaluation of such "simple" paths is optimized and
     * streamlined.
     * @return <code>true if this path is simple
     */
    public synchronized boolean isSimplePath() {
        if (!basicKnown) {
            basicKnown = true;
            basic = true;
            Step[] steps = getSteps();
            for (int i = 0; i < steps.length; i++) {
                if (!isSimpleStep(steps[i])) {
                    basic = false;
                    break;
                }
            }
        }
        return basic;
    }

    /**
     * A Step is "simple" if it takes one of these forms: ".", "/foo",
     * "@bar", "/foo[3]". If there are predicates, they should be
     * context independent for the step to still be considered simple.
     * @param step the step to check
     * @return boolean
     */
    protected boolean isSimpleStep(Step step) {
        if (step.getAxis() == Compiler.AXIS_SELF) {
            NodeTest nodeTest = step.getNodeTest();
            if (!(nodeTest instanceof NodeTypeTest)) {
                return false;
            }
            int nodeType = ((NodeTypeTest) nodeTest).getNodeType();
            if (nodeType != Compiler.NODE_TYPE_NODE) {
                return false;
            }
            return areBasicPredicates(step.getPredicates());
        }
        if (step.getAxis() == Compiler.AXIS_CHILD
                || step.getAxis() == Compiler.AXIS_ATTRIBUTE) {
            NodeTest nodeTest = step.getNodeTest();
            if (!(nodeTest instanceof NodeNameTest)) {
                return false;
            }
            if (((NodeNameTest) nodeTest).isWildcard()) {
                return false;
            }
            return areBasicPredicates(step.getPredicates());
        }
        return false;
    }

    /**
     * Learn whether the elements of the specified array are "basic" predicates.
     * @param predicates the Expression[] to check
     * @return boolean
     */
    protected boolean areBasicPredicates(Expression[] predicates) {
        if (predicates != null && predicates.length != 0) {
            boolean firstIndex = true;
            for (int i = 0; i < predicates.length; i++) {
                if (predicates[i] instanceof NameAttributeTest) {
                    if (((NameAttributeTest) predicates[i])
                        .getNameTestExpression()
                        .isContextDependent()) {
                        return false;
                    }
                }
                else if (predicates[i].isContextDependent()) {
                    return false;
                }
                else {
                    if (!firstIndex) {
                        return false;
                    }
                    firstIndex = false;
                }
            }
        }
        return true;
    }

    /**
     * Given a root context, walks a path therefrom and finds the
     * pointer to the first element matching the path.
     * @param context evaluation context
     * @return Pointer
     */
    protected Pointer getSingleNodePointerForSteps(EvalContext context) {
        if (steps.length == 0) {
            return context.getSingleNodePointer();
        }

        if (isSimplePath()) {
            NodePointer ptr = (NodePointer) context.getSingleNodePointer();
            return SimplePathInterpreter.interpretSimpleLocationPath(
                context,
                ptr,
                steps);
        }
        return searchForPath(context);
    }

    /**
     * The idea here is to return a NullPointer rather than null if that's at
     * all possible. Take for example this path: "//map/key". Let's say, "map"
     * is an existing node, but "key" is not there. We will create a
     * NullPointer that can be used to set/create the "key" property.
     * <p>
     * However, a path like "//key" would still produce null, because we have
     * no way of knowing where "key" would be if it existed.
     * </p>
     * <p>
     * To accomplish this, we first try the path itself. If it does not find
     * anything, we chop off last step of the path, as long as it is a simple
     * one like child:: or attribute:: and try to evaluate the truncated path.
     * If it finds exactly one node - create a NullPointer and return. If it
     * fails, chop off another step and repeat. If it finds more than one
     * location - return null.
     * </p>
     * @param context evaluation context
     * @return Pointer
     */
    protected Pointer searchForPath(EvalContext context) {
        EvalContext ctx = buildContextChain(context, steps.length, true);
        Pointer pointer = ctx.getSingleNodePointer();

        if (pointer != null) {
            return pointer;
        }

        for (int i = steps.length; --i > 0;) {
            if (!isSimpleStep(steps[i])) {
                return null;
            }
            ctx = buildContextChain(context, i, true);
            if (ctx.hasNext()) {
                Pointer partial = (Pointer) ctx.next();
                if (ctx.hasNext()) {
                    // If we find another location - the search is
                    // ambiguous, so we report failure
                    return null;
                }
                if (partial instanceof NodePointer) {
                    return SimplePathInterpreter.createNullPointer(
                            context,
                            (NodePointer) partial,
                            steps,
                            i);
                }
            }
        }
        return null;
    }

    /**
     * Given a root context, walks a path therefrom and builds a context
     * that contains all nodes matching the path.
     * @param context evaluation context
     * @return EvaluationContext
     */
    protected EvalContext evalSteps(EvalContext context) {
        return buildContextChain(context, steps.length, false);
    }

    /**
     * Build a context from a chain of contexts.
     * @param context evaluation context
     * @param stepCount number of steps to descend
     * @param createInitialContext whether to create the initial context
     * @return created context
     */
    protected EvalContext buildContextChain(
            EvalContext context,
            int stepCount,
            boolean createInitialContext) {
        if (createInitialContext) {
            context = new InitialContext(context);
        }
        if (steps.length == 0) {
            return context;
        }
        for (int i = 0; i < stepCount; i++) {
            context =
                createContextForStep(
                    context,
                    steps[i].getAxis(),
                    steps[i].getNodeTest());
            Expression[] predicates = steps[i].getPredicates();
            if (predicates != null) {
                for (int j = 0; j < predicates.length; j++) {
                    if (j != 0) {
                        context = new UnionContext(context, new EvalContext[]{context});
                    }
                    context = new PredicateContext(context, predicates[j]);
                }
            }
        }
        return context;
    }

    /**
     * Different axes are serviced by different contexts. This method
     * allocates the right context for the supplied step.
     * @param context evaluation context
     * @param axis code
     * @param nodeTest node test
     * @return EvalContext
     */
    protected EvalContext createContextForStep(
        EvalContext context,
        int axis,
        NodeTest nodeTest) {
        if (nodeTest instanceof NodeNameTest) {
            QName qname = ((NodeNameTest) nodeTest).getNodeName();
            String prefix = qname.getPrefix();
            if (prefix != null) {
                String namespaceURI = context.getJXPathContext()
                        .getNamespaceURI(prefix);
                nodeTest = new NodeNameTest(qname, namespaceURI);
            }
        }

        switch (axis) {
        case Compiler.AXIS_ANCESTOR :
            return new AncestorContext(context, false, nodeTest);
        case Compiler.AXIS_ANCESTOR_OR_SELF :
            return new AncestorContext(context, true, nodeTest);
        case Compiler.AXIS_ATTRIBUTE :
            return new AttributeContext(context, nodeTest);
        case Compiler.AXIS_CHILD :
            return new ChildContext(context, nodeTest, false, false);
        case Compiler.AXIS_DESCENDANT :
            return new DescendantContext(context, false, nodeTest);
        case Compiler.AXIS_DESCENDANT_OR_SELF :
            return new DescendantContext(context, true, nodeTest);
        case Compiler.AXIS_FOLLOWING :
            return new PrecedingOrFollowingContext(context, nodeTest, false);
        case Compiler.AXIS_FOLLOWING_SIBLING :
            return new ChildContext(context, nodeTest, true, false);
        case Compiler.AXIS_NAMESPACE :
            return new NamespaceContext(context, nodeTest);
        case Compiler.AXIS_PARENT :
            return new ParentContext(context, nodeTest);
        case Compiler.AXIS_PRECEDING :
            return new PrecedingOrFollowingContext(context, nodeTest, true);
        case Compiler.AXIS_PRECEDING_SIBLING :
            return new ChildContext(context, nodeTest, true, true);
        case Compiler.AXIS_SELF :
            return new SelfContext(context, nodeTest);
        default:
            return null; // Never happens
        }
    }
}