Commons JXPath example source code file (ExpressionPath.java)

This example Commons JXPath source code file (ExpressionPath.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

coreoperation, evalcontext, evalcontext, expression, expression, expressionpath, expressionpath, initialcontext, nodepointer, object, object, step, stringbuffer, unioncontext

The Commons JXPath ExpressionPath.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.ri.EvalContext;
import org.apache.commons.jxpath.ri.axes.InitialContext;
import org.apache.commons.jxpath.ri.axes.NodeSetContext;
import org.apache.commons.jxpath.ri.axes.PredicateContext;
import org.apache.commons.jxpath.ri.axes.SimplePathInterpreter;
import org.apache.commons.jxpath.ri.axes.UnionContext;
import org.apache.commons.jxpath.ri.model.NodePointer;

/**
 * An  element of the parse tree that represents an expression path, which is a
 * path that starts with an expression like a function call: <code>getFoo(.)
 * /bar</code>.
 *
 * @author Dmitri Plotnikov
 * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $
 */
public class ExpressionPath extends Path {

    private Expression expression;
    private Expression[] predicates;

    private boolean basicKnown = false;
    private boolean basic;

    /**
     * Create a new ExpressionPath.
     * @param expression Expression
     * @param predicates to execute
     * @param steps navigation
     */
    public ExpressionPath(Expression expression, Expression[] predicates,
            Step[] steps) {
        super(steps);
        this.expression = expression;
        this.predicates = predicates;
    }

    /**
     * Get the expression.
     * @return Expression
     */
    public Expression getExpression() {
        return expression;
    }

    /**
     * Predicates are the expressions in brackets that may follow
     * the root expression of the path.
     * @return Expression[]
     */
    public Expression[] getPredicates() {
        return predicates;
    }

    /**
     * Returns true if the root expression or any of the
     * predicates or the path steps are context dependent.
     * @return boolean
     */
    public boolean computeContextDependent() {
        if (expression.isContextDependent()) {
            return true;
        }
        if (predicates != null) {
            for (int i = 0; i < predicates.length; i++) {
                if (predicates[i].isContextDependent()) {
                    return true;
                }
            }
        }
        return super.computeContextDependent();
    }

    /**
     * Recognized paths formatted as <code>$x[3]/foo[2].  The
     * evaluation of such "simple" paths is optimized and streamlined.
     * @return boolean
     */
    public synchronized boolean isSimpleExpressionPath() {
        if (!basicKnown) {
            basicKnown = true;
            basic = isSimplePath() && areBasicPredicates(getPredicates());
        }
        return basic;
    }

    public String toString() {
        StringBuffer buffer = new StringBuffer();
        if (expression instanceof CoreOperation
            || expression instanceof ExpressionPath
            || expression instanceof LocationPath) {
            buffer.append('(');
            buffer.append(expression);
            buffer.append(')');
        }
        else {
            buffer.append(expression);
        }
        if (predicates != null) {
            for (int i = 0; i < predicates.length; i++) {
                buffer.append('[');
                buffer.append(predicates[i]);
                buffer.append(']');
            }
        }

        Step[] steps = getSteps();
        if (steps != null) {
            for (int i = 0; i < steps.length; i++) {
                buffer.append("/");
                buffer.append(steps[i]);
            }
        }
        return buffer.toString();
    }

    public Object compute(EvalContext context) {
        return expressionPath(context, false);
    }

    public Object computeValue(EvalContext context) {
        return expressionPath(context, true);
    }

    /**
     * Walks an expression path (a path that starts with an expression)
     * @param evalContext base context
     * @param firstMatch whether to return the first match found
     * @return Object found
     */
    protected Object expressionPath(EvalContext evalContext, boolean firstMatch) {
        Object value = expression.compute(evalContext);
        EvalContext context;
        if (value instanceof InitialContext) {
            // This is an optimization. We can avoid iterating through a
            // collection if the context bean is in fact one.
            context = (InitialContext) value;
        }
        else if (value instanceof EvalContext) {
            // UnionContext will collect all values from the "value" context
            // and treat the whole thing as a big collection.
            context =
                new UnionContext(
                    evalContext,
                    new EvalContext[] {(EvalContext) value });
        }
        else {
            context = evalContext.getRootContext().getConstantContext(value);
        }

        if (firstMatch
            && isSimpleExpressionPath()
            && !(context instanceof NodeSetContext)) {
            EvalContext ctx = context;
            NodePointer ptr = (NodePointer) ctx.getSingleNodePointer();
            if (ptr != null
                && (ptr.getIndex() == NodePointer.WHOLE_COLLECTION
                    || predicates == null
                    || predicates.length == 0)) {
                return SimplePathInterpreter.interpretSimpleExpressionPath(
                    evalContext,
                    ptr,
                    predicates,
                    getSteps());
            }
        }
        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 firstMatch ? (Object) getSingleNodePointerForSteps(context)
                : evalSteps(context);
    }
}