    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.tree.xpath;
    018
    019import java.util.Collections;
    020import java.util.LinkedList;
    021import java.util.List;
    022import java.util.StringTokenizer;
    023import java.util.stream.Collectors;
    024
    025import org.apache.commons.configuration2.tree.ExpressionEngine;
    026import org.apache.commons.configuration2.tree.NodeAddData;
    027import org.apache.commons.configuration2.tree.NodeHandler;
    028import org.apache.commons.configuration2.tree.QueryResult;
    029import org.apache.commons.jxpath.JXPathContext;
    030import org.apache.commons.jxpath.ri.JXPathContextReferenceImpl;
    031import org.apache.commons.lang3.StringUtils;
    032
    033/**
    034 * <p>
    035 * A specialized implementation of the {@code ExpressionEngine} interface that is able to evaluate XPATH expressions.
    036 * </p>
    037 * <p>
    038 * This class makes use of <a href="https://commons.apache.org/jxpath/"> Commons JXPath</a> for handling XPath
    039 * expressions and mapping them to the nodes of a hierarchical configuration. This makes the rich and powerful XPATH
    040 * syntax available for accessing properties from a configuration object.
    041 * </p>
    042 * <p>
    043 * For selecting properties arbitrary XPATH expressions can be used, which select single or multiple configuration
    044 * nodes. The associated {@code Configuration} instance will directly pass the specified property keys into this engine.
    045 * If a key is not syntactically correct, an exception will be thrown.
    046 * </p>
    047 * <p>
    048 * For adding new properties, this expression engine uses a specific syntax: the &quot;key&quot; of a new property must
    049 * consist of two parts that are separated by whitespace:
    050 * </p>
    051 * <ol>
    052 * <li>An XPATH expression selecting a single node, to which the new element(s) are to be added. This can be an
    053 * arbitrary complex expression, but it must select exactly one node, otherwise an exception will be thrown.</li>
    054 * <li>The name of the new element(s) to be added below this parent node. Here either a single node name or a complete
    055 * path of nodes (separated by the &quot;/&quot; character or &quot;@&quot; for an attribute) can be specified.</li>
    056 * </ol>
    057 * <p>
    058 * Some examples for valid keys that can be passed into the configuration's {@code addProperty()} method follow:
    059 * </p>
    060 *
    061 * <pre>
    062 * &quot;/tables/table[1] type&quot;
    063 * </pre>
    064 *
    065 * <p>
    066 * This will add a new {@code type} node as a child of the first {@code table} element.
    067 * </p>
    068 *
    069 * <pre>
    070 * &quot;/tables/table[1] @type&quot;
    071 * </pre>
    072 *
    073 * <p>
    074 * Similar to the example above, but this time a new attribute named {@code type} will be added to the first
    075 * {@code table} element.
    076 * </p>
    077 *
    078 * <pre>
    079 * &quot;/tables table/fields/field/name&quot;
    080 * </pre>
    081 *
    082 * <p>
    083 * This example shows how a complex path can be added. Parent node is the {@code tables} element. Here a new branch
    084 * consisting of the nodes {@code table}, {@code fields}, {@code field}, and {@code name} will be added.
    085 * </p>
    086 *
    087 * <pre>
    088 * &quot;/tables table/fields/field@type&quot;
    089 * </pre>
    090 *
    091 * <p>
    092 * This is similar to the last example, but in this case a complex path ending with an attribute is defined.
    093 * </p>
    094 * <p>
    095 * <strong>Note:</strong> This extended syntax for adding properties only works with the {@code addProperty()} method.
    096 * {@code setProperty()} does not support creating new nodes this way.
    097 * </p>
    098 * <p>
    099 * From version 1.7 on, it is possible to use regular keys in calls to {@code addProperty()} (i.e. keys that do not have
    100 * to contain a whitespace as delimiter). In this case the key is evaluated, and the biggest part pointing to an
    101 * existing node is determined. The remaining part is then added as new path. As an example consider the key
    102 * </p>
    103 *
    104 * <pre>
    105 * &quot;tables/table[last()]/fields/field/name&quot;
    106 * </pre>
    107 *
    108 * <p>
    109 * If the key does not point to an existing node, the engine will check the paths
    110 * {@code "tables/table[last()]/fields/field"}, {@code "tables/table[last()]/fields"}, {@code "tables/table[last()]"},
    111 * and so on, until a key is found which points to a node. Let's assume that the last key listed above can be resolved
    112 * in this way. Then from this key the following key is derived: {@code "tables/table[last()] fields/field/name"} by
    113 * appending the remaining part after a whitespace. This key can now be processed using the original algorithm. Keys of
    114 * this form can also be used with the {@code setProperty()} method. However, it is still recommended to use the old
    115 * format because it makes explicit at which position new nodes should be added. For keys without a whitespace delimiter
    116 * there may be ambiguities.
    117 * </p>
    118 *
    119 * @since 1.3
    120 */
    121public class XPathExpressionEngine implements ExpressionEngine {
    122    /** Constant for the path delimiter. */
    123    static final String PATH_DELIMITER = "/";
    124
    125    /** Constant for the attribute delimiter. */
    126    static final String ATTR_DELIMITER = "@";
    127
    128    /** Constant for the delimiters for splitting node paths. */
    129    private static final String NODE_PATH_DELIMITERS = PATH_DELIMITER + ATTR_DELIMITER;
    130
    131    /**
    132     * Constant for a space which is used as delimiter in keys for adding properties.
    133     */
    134    private static final String SPACE = " ";
    135
    136    /** Constant for a default size of a key buffer. */
    137    private static final int BUF_SIZE = 128;
    138
    139    /** Constant for the start of an index expression. */
    140    private static final char START_INDEX = '[';
    141
    142    /** Constant for the end of an index expression. */
    143    private static final char END_INDEX = ']';
    144
    145    // static initializer: registers the configuration node pointer factory
    146    static {
    147        JXPathContextReferenceImpl.addNodePointerFactory(new ConfigurationNodePointerFactory());
    148    }
    149
    150    /**
    151     * Converts the objects returned as query result from the JXPathContext to query result objects.
    152     *
    153     * @param results the list with results from the context
    154     * @param <T> the type of results to be produced
    155     * @return the result list
    156     */
    157    private static <T> List<QueryResult<T>> convertResults(final List<?> results) {
    158        return results.stream().map(res -> (QueryResult<T>) createResult(res)).collect(Collectors.toList());
    159    }
    160
    161    /**
    162     * Creates a {@code QueryResult} object from the given result object of a query. Because of the node pointers involved
    163     * result objects can only be of two types:
    164     * <ul>
    165     * <li>nodes of type T</li>
    166     * <li>attribute results already wrapped in {@code QueryResult} objects</li>
    167     * </ul>
    168     * This method performs a corresponding cast. Warnings can be suppressed because of the implementation of the query
    169     * functionality.
    170     *
    171     * @param resObj the query result object
    172     * @param <T> the type of the result to be produced
    173     * @return the {@code QueryResult}
    174     */
    175    @SuppressWarnings("unchecked")
    176    private static <T> QueryResult<T> createResult(final Object resObj) {
    177        if (resObj instanceof QueryResult) {
    178            return (QueryResult<T>) resObj;
    179        }
    180        return QueryResult.createNodeResult((T) resObj);
    181    }
    182
    183    /**
    184     * Determines the index of the given child node in the node list of its parent.
    185     *
    186     * @param parent the parent node
    187     * @param child the child node
    188     * @param handler the node handler
    189     * @param <T> the type of the nodes involved
    190     * @return the index of this child node
    191     */
    192    private static <T> int determineIndex(final T parent, final T child, final NodeHandler<T> handler) {
    193        return handler.getChildren(parent, handler.nodeName(child)).indexOf(child) + 1;
    194    }
    195
    196    /**
    197     * Determines the position of the separator in a key for adding new properties. If no delimiter is found, result is -1.
    198     *
    199     * @param key the key
    200     * @return the position of the delimiter
    201     */
    202    private static int findKeySeparator(final String key) {
    203        int index = key.length() - 1;
    204        while (index >= 0 && !Character.isWhitespace(key.charAt(index))) {
    205            index--;
    206        }
    207        return index;
    208    }
    209
    210    /**
    211     * Helper method for throwing an exception about an invalid path.
    212     *
    213     * @param path the invalid path
    214     * @param msg the exception message
    215     */
    216    private static void invalidPath(final String path, final String msg) {
    217        throw new IllegalArgumentException("Invalid node path: \"" + path + "\" " + msg);
    218    }
    219
    220    /** The internally used context factory. */
    221    private final XPathContextFactory contextFactory;
    222
    223    /**
    224     * Creates a new instance of {@code XPathExpressionEngine} with default settings.
    225     */
    226    public XPathExpressionEngine() {
    227        this(new XPathContextFactory());
    228    }
    229
    230    /**
    231     * Creates a new instance of {@code XPathExpressionEngine} and sets the context factory. This constructor is mainly used
    232     * for testing purposes.
    233     *
    234     * @param factory the {@code XPathContextFactory}
    235     */
    236    XPathExpressionEngine(final XPathContextFactory factory) {
    237        contextFactory = factory;
    238    }
    239
    240    @Override
    241    public String attributeKey(final String parentKey, final String attributeName) {
    242        final StringBuilder buf = new StringBuilder(
    243            StringUtils.length(parentKey) + StringUtils.length(attributeName) + PATH_DELIMITER.length() + ATTR_DELIMITER.length());
    244        if (StringUtils.isNotEmpty(parentKey)) {
    245            buf.append(parentKey).append(PATH_DELIMITER);
    246        }
    247        buf.append(ATTR_DELIMITER).append(attributeName);
    248        return buf.toString();
    249    }
    250
    251    /**
    252     * {@inheritDoc} This implementation works similar to {@code nodeKey()}, but always adds an index expression to the
    253     * resulting key.
    254     */
    255    @Override
    256    public <T> String canonicalKey(final T node, final String parentKey, final NodeHandler<T> handler) {
    257        final T parent = handler.getParent(node);
    258        if (parent == null) {
    259            // this is the root node
    260            return StringUtils.defaultString(parentKey);
    261        }
    262
    263        final StringBuilder buf = new StringBuilder(BUF_SIZE);
    264        if (StringUtils.isNotEmpty(parentKey)) {
    265            buf.append(parentKey).append(PATH_DELIMITER);
    266        }
    267        buf.append(handler.nodeName(node));
    268        buf.append(START_INDEX);
    269        buf.append(determineIndex(parent, node, handler));
    270        buf.append(END_INDEX);
    271        return buf.toString();
    272    }
    273
    274    /**
    275     * Creates the {@code JXPathContext} to be used for executing a query. This method delegates to the context factory.
    276     *
    277     * @param root the configuration root node
    278     * @param handler the node handler
    279     * @return the new context
    280     */
    281    private <T> JXPathContext createContext(final T root, final NodeHandler<T> handler) {
    282        return getContextFactory().createContext(root, handler);
    283    }
    284
    285    /**
    286     * Creates a {@code NodeAddData} object as a result of a {@code prepareAdd()} operation. This method interprets the
    287     * passed in path of the new node.
    288     *
    289     * @param path the path of the new node
    290     * @param parentNodeResult the parent node
    291     * @param <T> the type of the nodes involved
    292     */
    293    <T> NodeAddData<T> createNodeAddData(final String path, final QueryResult<T> parentNodeResult) {
    294        if (parentNodeResult.isAttributeResult()) {
    295            invalidPath(path, " cannot add properties to an attribute.");
    296        }
    297        final List<String> pathNodes = new LinkedList<>();
    298        String lastComponent = null;
    299        boolean attr = false;
    300        boolean first = true;
    301
    302        final StringTokenizer tok = new StringTokenizer(path, NODE_PATH_DELIMITERS, true);
    303        while (tok.hasMoreTokens()) {
    304            final String token = tok.nextToken();
    305            if (PATH_DELIMITER.equals(token)) {
    306                if (attr) {
    307                    invalidPath(path, " contains an attribute" + " delimiter at a disallowed position.");
    308                }
    309                if (lastComponent == null) {
    310                    invalidPath(path, " contains a '/' at a disallowed position.");
    311                }
    312                pathNodes.add(lastComponent);
    313                lastComponent = null;
    314            } else if (ATTR_DELIMITER.equals(token)) {
    315                if (attr) {
    316                    invalidPath(path, " contains multiple attribute delimiters.");
    317                }
    318                if (lastComponent == null && !first) {
    319                    invalidPath(path, " contains an attribute delimiter at a disallowed position.");
    320                }
    321                if (lastComponent != null) {
    322                    pathNodes.add(lastComponent);
    323                }
    324                attr = true;
    325                lastComponent = null;
    326            } else {
    327                lastComponent = token;
    328            }
    329            first = false;
    330        }
    331
    332        if (lastComponent == null) {
    333            invalidPath(path, "contains no components.");
    334        }
    335
    336        return new NodeAddData<>(parentNodeResult.getNode(), lastComponent, attr, pathNodes);
    337    }
    338
    339    /**
    340     * Tries to generate a key for adding a property. This method is called if a key was used for adding properties which
    341     * does not contain a space character. It splits the key at its single components and searches for the last existing
    342     * component. Then a key compatible key for adding properties is generated.
    343     *
    344     * @param root the root node of the configuration
    345     * @param key the key in question
    346     * @param handler the node handler
    347     * @return the key to be used for adding the property
    348     */
    349    private <T> String generateKeyForAdd(final T root, final String key, final NodeHandler<T> handler) {
    350        int pos = key.lastIndexOf(PATH_DELIMITER, key.length());
    351
    352        while (pos >= 0) {
    353            final String keyExisting = key.substring(0, pos);
    354            if (!query(root, keyExisting, handler).isEmpty()) {
    355                final StringBuilder buf = new StringBuilder(key.length() + 1);
    356                buf.append(keyExisting).append(SPACE);
    357                buf.append(key.substring(pos + 1));
    358                return buf.toString();
    359            }
    360            pos = key.lastIndexOf(PATH_DELIMITER, pos - 1);
    361        }
    362
    363        return SPACE + key;
    364    }
    365
    366    /**
    367     * Gets the {@code XPathContextFactory} used by this instance.
    368     *
    369     * @return the {@code XPathContextFactory}
    370     */
    371    XPathContextFactory getContextFactory() {
    372        return contextFactory;
    373    }
    374
    375    /**
    376     * {@inheritDoc} This implementation creates an XPATH expression that selects the given node (under the assumption that
    377     * the passed in parent key is valid). As the {@code nodeKey()} implementation of
    378     * {@link org.apache.commons.configuration2.tree.DefaultExpressionEngine DefaultExpressionEngine} this method does not
    379     * return indices for nodes. So all child nodes of a given parent with the same name have the same key.
    380     */
    381    @Override
    382    public <T> String nodeKey(final T node, final String parentKey, final NodeHandler<T> handler) {
    383        if (parentKey == null) {
    384            // name of the root node
    385            return StringUtils.EMPTY;
    386        }
    387        if (handler.nodeName(node) == null) {
    388            // paranoia check for undefined node names
    389            return parentKey;
    390        }
    391        final StringBuilder buf = new StringBuilder(parentKey.length() + handler.nodeName(node).length() + PATH_DELIMITER.length());
    392        if (!parentKey.isEmpty()) {
    393            buf.append(parentKey);
    394            buf.append(PATH_DELIMITER);
    395        }
    396        buf.append(handler.nodeName(node));
    397        return buf.toString();
    398    }
    399
    400    /**
    401     * {@inheritDoc} The expected format of the passed in key is explained in the class comment.
    402     */
    403    @Override
    404    public <T> NodeAddData<T> prepareAdd(final T root, final String key, final NodeHandler<T> handler) {
    405        if (key == null) {
    406            throw new IllegalArgumentException("prepareAdd: key must not be null!");
    407        }
    408
    409        String addKey = key;
    410        int index = findKeySeparator(addKey);
    411        if (index < 0) {
    412            addKey = generateKeyForAdd(root, addKey, handler);
    413            index = findKeySeparator(addKey);
    414        } else if (index >= addKey.length() - 1) {
    415            invalidPath(addKey, " new node path must not be empty.");
    416        }
    417
    418        final List<QueryResult<T>> nodes = query(root, addKey.substring(0, index).trim(), handler);
    419        if (nodes.size() != 1) {
    420            throw new IllegalArgumentException("prepareAdd: key '" + key + "' must select exactly one target node!");
    421        }
    422
    423        return createNodeAddData(addKey.substring(index).trim(), nodes.get(0));
    424    }
    425
    426    /**
    427     * {@inheritDoc} This implementation interprets the passed in key as an XPATH expression.
    428     */
    429    @Override
    430    public <T> List<QueryResult<T>> query(final T root, final String key, final NodeHandler<T> handler) {
    431        if (StringUtils.isEmpty(key)) {
    432            final QueryResult<T> result = createResult(root);
    433            return Collections.singletonList(result);
    434        }
    435        final JXPathContext context = createContext(root, handler);
    436        List<?> results = context.selectNodes(key);
    437        if (results == null) {
    438            results = Collections.emptyList();
    439        }
    440        return convertResults(results);
    441    }
    442}