    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.ArrayList;
    020import java.util.Collections;
    021import java.util.LinkedList;
    022import java.util.List;
    023import java.util.StringTokenizer;
    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
    036 * is able to evaluate XPATH expressions.
    037 * </p>
    038 * <p>
    039 * This class makes use of <a href="https://commons.apache.org/jxpath/"> Commons
    040 * JXPath</a> for handling XPath expressions and mapping them to the nodes of a
    041 * hierarchical configuration. This makes the rich and powerful XPATH syntax
    042 * available for accessing properties from a configuration object.
    043 * </p>
    044 * <p>
    045 * For selecting properties arbitrary XPATH expressions can be used, which
    046 * select single or multiple configuration nodes. The associated
    047 * {@code Configuration} instance will directly pass the specified property keys
    048 * into this engine. If a key is not syntactically correct, an exception will be
    049 * thrown.
    050 * </p>
    051 * <p>
    052 * For adding new properties, this expression engine uses a specific syntax: the
    053 * &quot;key&quot; of a new property must consist of two parts that are
    054 * separated by whitespace:
    055 * </p>
    056 * <ol>
    057 * <li>An XPATH expression selecting a single node, to which the new element(s)
    058 * are to be added. This can be an arbitrary complex expression, but it must
    059 * select exactly one node, otherwise an exception will be thrown.</li>
    060 * <li>The name of the new element(s) to be added below this parent node. Here
    061 * either a single node name or a complete path of nodes (separated by the
    062 * &quot;/&quot; character or &quot;@&quot; for an attribute) can be specified.</li>
    063 * </ol>
    064 * <p>
    065 * Some examples for valid keys that can be passed into the configuration's
    066 * {@code addProperty()} method follow:
    067 * </p>
    068 *
    069 * <pre>
    070 * &quot;/tables/table[1] type&quot;
    071 * </pre>
    072 *
    073 * <p>
    074 * This will add a new {@code type} node as a child of the first {@code table}
    075 * element.
    076 * </p>
    077 *
    078 * <pre>
    079 * &quot;/tables/table[1] @type&quot;
    080 * </pre>
    081 *
    082 * <p>
    083 * Similar to the example above, but this time a new attribute named
    084 * {@code type} will be added to the first {@code table} element.
    085 * </p>
    086 *
    087 * <pre>
    088 * &quot;/tables table/fields/field/name&quot;
    089 * </pre>
    090 *
    091 * <p>
    092 * This example shows how a complex path can be added. Parent node is the
    093 * {@code tables} element. Here a new branch consisting of the nodes
    094 * {@code table}, {@code fields}, {@code field}, and {@code name} will be added.
    095 * </p>
    096 *
    097 * <pre>
    098 * &quot;/tables table/fields/field@type&quot;
    099 * </pre>
    100 *
    101 * <p>
    102 * This is similar to the last example, but in this case a complex path ending
    103 * with an attribute is defined.
    104 * </p>
    105 * <p>
    106 * <strong>Note:</strong> This extended syntax for adding properties only works
    107 * with the {@code addProperty()} method. {@code setProperty()} does not support
    108 * creating new nodes this way.
    109 * </p>
    110 * <p>
    111 * From version 1.7 on, it is possible to use regular keys in calls to
    112 * {@code addProperty()} (i.e. keys that do not have to contain a whitespace as
    113 * delimiter). In this case the key is evaluated, and the biggest part pointing
    114 * to an existing node is determined. The remaining part is then added as new
    115 * path. As an example consider the key
    116 * </p>
    117 *
    118 * <pre>
    119 * &quot;tables/table[last()]/fields/field/name&quot;
    120 * </pre>
    121 *
    122 * <p>
    123 * If the key does not point to an existing node, the engine will check the
    124 * paths {@code "tables/table[last()]/fields/field"},
    125 * {@code "tables/table[last()]/fields"}, {@code "tables/table[last()]"}, and so
    126 * on, until a key is found which points to a node. Let's assume that the last
    127 * key listed above can be resolved in this way. Then from this key the
    128 * following key is derived: {@code "tables/table[last()] fields/field/name"} by
    129 * appending the remaining part after a whitespace. This key can now be
    130 * processed using the original algorithm. Keys of this form can also be used
    131 * with the {@code setProperty()} method. However, it is still recommended to
    132 * use the old format because it makes explicit at which position new nodes
    133 * should be added. For keys without a whitespace delimiter there may be
    134 * ambiguities.
    135 * </p>
    136 *
    137 * @since 1.3
    138 */
    139public class XPathExpressionEngine implements ExpressionEngine
    140{
    141    /** Constant for the path delimiter. */
    142    static final String PATH_DELIMITER = "/";
    143
    144    /** Constant for the attribute delimiter. */
    145    static final String ATTR_DELIMITER = "@";
    146
    147    /** Constant for the delimiters for splitting node paths. */
    148    private static final String NODE_PATH_DELIMITERS = PATH_DELIMITER
    149            + ATTR_DELIMITER;
    150
    151    /**
    152     * Constant for a space which is used as delimiter in keys for adding
    153     * properties.
    154     */
    155    private static final String SPACE = " ";
    156
    157    /** Constant for a default size of a key buffer. */
    158    private static final int BUF_SIZE = 128;
    159
    160    /** Constant for the start of an index expression. */
    161    private static final char START_INDEX = '[';
    162
    163    /** Constant for the end of an index expression. */
    164    private static final char END_INDEX = ']';
    165
    166    /** The internally used context factory. */
    167    private final XPathContextFactory contextFactory;
    168
    169    /**
    170     * Creates a new instance of {@code XPathExpressionEngine} with default
    171     * settings.
    172     */
    173    public XPathExpressionEngine()
    174    {
    175        this(new XPathContextFactory());
    176    }
    177
    178    /**
    179     * Creates a new instance of {@code XPathExpressionEngine} and sets the
    180     * context factory. This constructor is mainly used for testing purposes.
    181     *
    182     * @param factory the {@code XPathContextFactory}
    183     */
    184    XPathExpressionEngine(final XPathContextFactory factory)
    185    {
    186        contextFactory = factory;
    187    }
    188
    189    /**
    190     * {@inheritDoc} This implementation interprets the passed in key as an XPATH
    191     * expression.
    192     */
    193    @Override
    194    public <T> List<QueryResult<T>> query(final T root, final String key,
    195            final NodeHandler<T> handler)
    196    {
    197        if (StringUtils.isEmpty(key))
    198        {
    199            final QueryResult<T> result = createResult(root);
    200            return Collections.singletonList(result);
    201        }
    202        final JXPathContext context = createContext(root, handler);
    203        List<?> results = context.selectNodes(key);
    204        if (results == null)
    205        {
    206            results = Collections.emptyList();
    207        }
    208        return convertResults(results);
    209    }
    210
    211    /**
    212     * {@inheritDoc} This implementation creates an XPATH expression that
    213     * selects the given node (under the assumption that the passed in parent
    214     * key is valid). As the {@code nodeKey()} implementation of
    215     * {@link org.apache.commons.configuration2.tree.DefaultExpressionEngine
    216     * DefaultExpressionEngine} this method does not return indices for nodes.
    217     * So all child nodes of a given parent with the same name have the same
    218     * key.
    219     */
    220    @Override
    221    public <T> String nodeKey(final T node, final String parentKey, final NodeHandler<T> handler)
    222    {
    223        if (parentKey == null)
    224        {
    225            // name of the root node
    226            return StringUtils.EMPTY;
    227        }
    228        else if (handler.nodeName(node) == null)
    229        {
    230            // paranoia check for undefined node names
    231            return parentKey;
    232        }
    233
    234        else
    235        {
    236            final StringBuilder buf =
    237                    new StringBuilder(parentKey.length()
    238                            + handler.nodeName(node).length()
    239                            + PATH_DELIMITER.length());
    240            if (parentKey.length() > 0)
    241            {
    242                buf.append(parentKey);
    243                buf.append(PATH_DELIMITER);
    244            }
    245            buf.append(handler.nodeName(node));
    246            return buf.toString();
    247        }
    248    }
    249
    250    @Override
    251    public String attributeKey(final String parentKey, final String attributeName)
    252    {
    253        final StringBuilder buf =
    254                new StringBuilder(StringUtils.length(parentKey)
    255                        + StringUtils.length(attributeName)
    256                        + PATH_DELIMITER.length() + ATTR_DELIMITER.length());
    257        if (StringUtils.isNotEmpty(parentKey))
    258        {
    259            buf.append(parentKey).append(PATH_DELIMITER);
    260        }
    261        buf.append(ATTR_DELIMITER).append(attributeName);
    262        return buf.toString();
    263    }
    264
    265    /**
    266     * {@inheritDoc} This implementation works similar to {@code nodeKey()}, but
    267     * always adds an index expression to the resulting key.
    268     */
    269    @Override
    270    public <T> String canonicalKey(final T node, final String parentKey,
    271            final NodeHandler<T> handler)
    272    {
    273        final T parent = handler.getParent(node);
    274        if (parent == null)
    275        {
    276            // this is the root node
    277            return StringUtils.defaultString(parentKey);
    278        }
    279
    280        final StringBuilder buf = new StringBuilder(BUF_SIZE);
    281        if (StringUtils.isNotEmpty(parentKey))
    282        {
    283            buf.append(parentKey).append(PATH_DELIMITER);
    284        }
    285        buf.append(handler.nodeName(node));
    286        buf.append(START_INDEX);
    287        buf.append(determineIndex(parent, node, handler));
    288        buf.append(END_INDEX);
    289        return buf.toString();
    290    }
    291
    292    /**
    293     * {@inheritDoc} The expected format of the passed in key is explained in
    294     * the class comment.
    295     */
    296    @Override
    297    public <T> NodeAddData<T> prepareAdd(final T root, final String key,
    298            final NodeHandler<T> handler)
    299    {
    300        if (key == null)
    301        {
    302            throw new IllegalArgumentException(
    303                    "prepareAdd: key must not be null!");
    304        }
    305
    306        String addKey = key;
    307        int index = findKeySeparator(addKey);
    308        if (index < 0)
    309        {
    310            addKey = generateKeyForAdd(root, addKey, handler);
    311            index = findKeySeparator(addKey);
    312        }
    313        else if (index >= addKey.length() - 1)
    314        {
    315            invalidPath(addKey, " new node path must not be empty.");
    316        }
    317
    318        final List<QueryResult<T>> nodes =
    319                query(root, addKey.substring(0, index).trim(), handler);
    320        if (nodes.size() != 1)
    321        {
    322            throw new IllegalArgumentException("prepareAdd: key '" + key
    323                    + "' must select exactly one target node!");
    324        }
    325
    326        return createNodeAddData(addKey.substring(index).trim(), nodes.get(0));
    327    }
    328
    329    /**
    330     * Creates the {@code JXPathContext} to be used for executing a query. This
    331     * method delegates to the context factory.
    332     *
    333     * @param root the configuration root node
    334     * @param handler the node handler
    335     * @return the new context
    336     */
    337    private <T> JXPathContext createContext(final T root, final NodeHandler<T> handler)
    338    {
    339        return getContextFactory().createContext(root, handler);
    340    }
    341
    342    /**
    343     * Creates a {@code NodeAddData} object as a result of a
    344     * {@code prepareAdd()} operation. This method interprets the passed in path
    345     * of the new node.
    346     *
    347     * @param path the path of the new node
    348     * @param parentNodeResult the parent node
    349     * @param <T> the type of the nodes involved
    350     */
    351    <T> NodeAddData<T> createNodeAddData(final String path,
    352            final QueryResult<T> parentNodeResult)
    353    {
    354        if (parentNodeResult.isAttributeResult())
    355        {
    356            invalidPath(path, " cannot add properties to an attribute.");
    357        }
    358        final List<String> pathNodes = new LinkedList<>();
    359        String lastComponent = null;
    360        boolean attr = false;
    361        boolean first = true;
    362
    363        final StringTokenizer tok =
    364                new StringTokenizer(path, NODE_PATH_DELIMITERS, true);
    365        while (tok.hasMoreTokens())
    366        {
    367            final String token = tok.nextToken();
    368            if (PATH_DELIMITER.equals(token))
    369            {
    370                if (attr)
    371                {
    372                    invalidPath(path, " contains an attribute"
    373                            + " delimiter at a disallowed position.");
    374                }
    375                if (lastComponent == null)
    376                {
    377                    invalidPath(path,
    378                            " contains a '/' at a disallowed position.");
    379                }
    380                pathNodes.add(lastComponent);
    381                lastComponent = null;
    382            }
    383
    384            else if (ATTR_DELIMITER.equals(token))
    385            {
    386                if (attr)
    387                {
    388                    invalidPath(path,
    389                            " contains multiple attribute delimiters.");
    390                }
    391                if (lastComponent == null && !first)
    392                {
    393                    invalidPath(path,
    394                            " contains an attribute delimiter at a disallowed position.");
    395                }
    396                if (lastComponent != null)
    397                {
    398                    pathNodes.add(lastComponent);
    399                }
    400                attr = true;
    401                lastComponent = null;
    402            }
    403
    404            else
    405            {
    406                lastComponent = token;
    407            }
    408            first = false;
    409        }
    410
    411        if (lastComponent == null)
    412        {
    413            invalidPath(path, "contains no components.");
    414        }
    415
    416        return new NodeAddData<>(parentNodeResult.getNode(), lastComponent,
    417                attr, pathNodes);
    418    }
    419
    420    /**
    421     * Returns the {@code XPathContextFactory} used by this instance.
    422     *
    423     * @return the {@code XPathContextFactory}
    424     */
    425    XPathContextFactory getContextFactory()
    426    {
    427        return contextFactory;
    428    }
    429
    430    /**
    431     * Tries to generate a key for adding a property. This method is called if a
    432     * key was used for adding properties which does not contain a space
    433     * character. It splits the key at its single components and searches for
    434     * the last existing component. Then a key compatible key for adding
    435     * properties is generated.
    436     *
    437     * @param root the root node of the configuration
    438     * @param key the key in question
    439     * @param handler the node handler
    440     * @return the key to be used for adding the property
    441     */
    442    private <T> String generateKeyForAdd(final T root, final String key,
    443            final NodeHandler<T> handler)
    444    {
    445        int pos = key.lastIndexOf(PATH_DELIMITER, key.length());
    446
    447        while (pos >= 0)
    448        {
    449            final String keyExisting = key.substring(0, pos);
    450            if (!query(root, keyExisting, handler).isEmpty())
    451            {
    452                final StringBuilder buf = new StringBuilder(key.length() + 1);
    453                buf.append(keyExisting).append(SPACE);
    454                buf.append(key.substring(pos + 1));
    455                return buf.toString();
    456            }
    457            pos = key.lastIndexOf(PATH_DELIMITER, pos - 1);
    458        }
    459
    460        return SPACE + key;
    461    }
    462
    463    /**
    464     * Determines the index of the given child node in the node list of its
    465     * parent.
    466     *
    467     * @param parent the parent node
    468     * @param child the child node
    469     * @param handler the node handler
    470     * @param <T> the type of the nodes involved
    471     * @return the index of this child node
    472     */
    473    private static <T> int determineIndex(final T parent, final T child,
    474            final NodeHandler<T> handler)
    475    {
    476        return handler.getChildren(parent, handler.nodeName(child)).indexOf(
    477                child) + 1;
    478    }
    479
    480    /**
    481     * Helper method for throwing an exception about an invalid path.
    482     *
    483     * @param path the invalid path
    484     * @param msg the exception message
    485     */
    486    private static void invalidPath(final String path, final String msg)
    487    {
    488        throw new IllegalArgumentException("Invalid node path: \"" + path
    489                + "\" " + msg);
    490    }
    491
    492    /**
    493     * Determines the position of the separator in a key for adding new
    494     * properties. If no delimiter is found, result is -1.
    495     *
    496     * @param key the key
    497     * @return the position of the delimiter
    498     */
    499    private static int findKeySeparator(final String key)
    500    {
    501        int index = key.length() - 1;
    502        while (index >= 0 && !Character.isWhitespace(key.charAt(index)))
    503        {
    504            index--;
    505        }
    506        return index;
    507    }
    508
    509    /**
    510     * Converts the objects returned as query result from the JXPathContext to
    511     * query result objects.
    512     *
    513     * @param results the list with results from the context
    514     * @param <T> the type of results to be produced
    515     * @return the result list
    516     */
    517    private static <T> List<QueryResult<T>> convertResults(final List<?> results)
    518    {
    519        final List<QueryResult<T>> queryResults =
    520                new ArrayList<>(results.size());
    521        for (final Object res : results)
    522        {
    523            final QueryResult<T> queryResult = createResult(res);
    524            queryResults.add(queryResult);
    525        }
    526        return queryResults;
    527    }
    528
    529    /**
    530     * Creates a {@code QueryResult} object from the given result object of a
    531     * query. Because of the node pointers involved result objects can only be
    532     * of two types:
    533     * <ul>
    534     * <li>nodes of type T</li>
    535     * <li>attribute results already wrapped in {@code QueryResult} objects</li>
    536     * </ul>
    537     * This method performs a corresponding cast. Warnings can be suppressed
    538     * because of the implementation of the query functionality.
    539     *
    540     * @param resObj the query result object
    541     * @param <T> the type of the result to be produced
    542     * @return the {@code QueryResult}
    543     */
    544    @SuppressWarnings("unchecked")
    545    private static <T> QueryResult<T> createResult(final Object resObj)
    546    {
    547        if (resObj instanceof QueryResult)
    548        {
    549            return (QueryResult<T>) resObj;
    550        }
    551        return QueryResult.createNodeResult((T) resObj);
    552    }
    553
    554    // static initializer: registers the configuration node pointer factory
    555    static
    556    {
    557        JXPathContextReferenceImpl
    558                .addNodePointerFactory(new ConfigurationNodePointerFactory());
    559    }
    560}