XPathHelper.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2016 Lachlan Dowding
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package permafrost.tundra.xml.xpath;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import permafrost.tundra.xml.dom.Nodes;
import java.util.Arrays;
import java.util.List;
import javax.xml.namespace.NamespaceContext;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

/**
 * A collection of convenience methods for working with XPath.
 */
public final class XPathHelper {
    /**
     * Disallow instantiation of this class.
     */
    private XPathHelper() {}

    /**
     * Evaluates if the given XPathExpression resolves against the given Node with the given content.
     *
     * @param context                   The XML content to select from.
     * @param expression                The XPath expression used to select from the given Node.
     * @param expectedContent           The expected contents of the selected nodes.
     * @return                          True if the XPath expression resolved against the given Node has the expected
     *                                  content.
     * @throws XPathExpressionException If a parsing error occurs.
     */
    public static boolean evaluate(Node context, XPathExpression expression, String ... expectedContent) throws XPathExpressionException {
        return evaluate(context, expression, expectedContent == null ? null : Arrays.asList(expectedContent));
    }

    /**
     * Evaluates if the given XPathExpression resolves against the given Node with the given content.
     *
     * @param context                   The XML content to select from.
     * @param expression                The XPath expression used to select from the given Node.
     * @param expectedContent           The expected contents of the selected nodes.
     * @return                          True if the XPath expression resolved against the given Node has the expected
     *                                  content.
     * @throws XPathExpressionException If a parsing error occurs.
     */
    public static boolean evaluate(Node context, XPathExpression expression, List<String> expectedContent) throws XPathExpressionException {
        boolean result = false;

        if (context != null && expression != null) {
            Nodes nodes = get(context, expression);

            if (nodes == null) {
                result = expectedContent == null;
            } else {
                List<String> actualContents = nodes.getTextContents();
                result = actualContents.equals(expectedContent);
            }
        }

        return result;
    }

    /**
     * Returns true if the given XPath expression can be found in the given XML content.
     *
     * @param context                   The content to query.
     * @param expression                The XPath expression to query against the give content.
     * @return                          True if the given XPath expression is found in the given XML content.
     * @throws XPathExpressionException If a parsing error occurs.
     */
    public static boolean exists(Node context, XPathExpression expression) throws XPathExpressionException {
        Nodes nodes = get(context, expression);
        return nodes != null;
    }

    /**
     * Returns the Nodes selected from the given Document by the given XPathExpression.
     *
     * @param context                   The XML content to select from.
     * @param expression                The XPath expression used to select from the given Node.
     * @return                          The Nodes list containing all the nodes selected from the given Node.
     * @throws XPathExpressionException If a parsing error occurs.
     */
    public static Nodes get(Node context, XPathExpression expression) throws XPathExpressionException {
        if (context == null || expression == null) return null;

        Nodes nodes = Nodes.of((NodeList)expression.evaluate(context, XPathConstants.NODESET));
        if (nodes != null && nodes.getLength() == 0) nodes = null; // normalize no results to null

        return nodes;
    }

    /**
     * Returns a compiled XPath expression.
     *
     * @param expression                The XPath expression as a String.
     * @return                          The compiled XPathExpression.
     * @throws XPathExpressionException If a parsing error occurs.
     */
    public static XPathExpression compile(String expression) throws XPathExpressionException {
        return compile(expression, (NamespaceContext)null);
    }

    /**
     * Returns a compiled XPath expression.
     *
     * @param expression                The XPath expression as a String.
     * @param namespaceContext          The namespace context used by the XPath expression.
     * @return                          The compiled XPathExpression.
     * @throws XPathExpressionException If a parsing error occurs.
     */
    public static XPathExpression compile(String expression, NamespaceContext namespaceContext) throws XPathExpressionException {
        XPath compiler = XPathFactory.newInstance().newXPath();
        if (namespaceContext != null) compiler.setNamespaceContext(namespaceContext);
        return compiler.compile(expression);
    }
}