    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;
    018
    019import org.apache.commons.lang3.StringUtils;
    020import org.apache.commons.lang3.builder.EqualsBuilder;
    021import org.apache.commons.lang3.builder.HashCodeBuilder;
    022import org.apache.commons.lang3.builder.ToStringBuilder;
    023
    024/**
    025 * <p>
    026 * A data class representing a single query result produced by an
    027 * {@link ExpressionEngine}.
    028 * </p>
    029 * <p>
    030 * When passing a key to the {@code query()} method of {@code ExpressionEngine}
    031 * the result can be a set of nodes or attributes - depending on the key. This
    032 * class can represent both types of results. The aim is to give a user of
    033 * {@code ExpressionEngine} all information needed for evaluating the results
    034 * returned.
    035 * </p>
    036 * <p>
    037 * Implementation note: Instances are immutable. They are created using the
    038 * static factory methods.
    039 * </p>
    040 *
    041 * @since 2.0
    042 * @param <T> the type of the result nodes
    043 */
    044public final class QueryResult<T>
    045{
    046    /** The node result. */
    047    private final T node;
    048
    049    /** The name of the result attribute. */
    050    private final String attributeName;
    051
    052    /**
    053     * Creates a new instance of {@code QueryResult}.
    054     *
    055     * @param nd the node
    056     * @param attr the attribute name
    057     */
    058    private QueryResult(final T nd, final String attr)
    059    {
    060        node = nd;
    061        attributeName = attr;
    062    }
    063
    064    /**
    065     * Creates a {@code QueryResult} instance representing the specified result
    066     * node.
    067     *
    068     * @param <T> the type of the result node
    069     * @param resultNode the result node
    070     * @return the newly created instance
    071     */
    072    public static <T> QueryResult<T> createNodeResult(final T resultNode)
    073    {
    074        return new QueryResult<>(resultNode, null);
    075    }
    076
    077    /**
    078     * Creates a {@code QueryResult} instance representing an attribute result.
    079     * An attribute result consists of the node the attribute belongs to and the
    080     * attribute name. (The value can be obtained based on this information.)
    081     *
    082     * @param parentNode the node which owns the attribute
    083     * @param attrName the attribute name
    084     * @param <T> the type of the parent node
    085     * @return the newly created instance
    086     */
    087    public static <T> QueryResult<T> createAttributeResult(final T parentNode,
    088                                                           final String attrName)
    089    {
    090        return new QueryResult<>(parentNode, attrName);
    091    }
    092
    093    /**
    094     * Returns the node referenced by this object. Depending on the result type,
    095     * this is either the result node or the parent node of the represented
    096     * attribute.
    097     *
    098     * @return the referenced node
    099     */
    100    public T getNode()
    101    {
    102        return node;
    103    }
    104
    105    /**
    106     * Returns the name of the attribute. This method is defined only for
    107     * results of type attribute.
    108     *
    109     * @return the attribute name
    110     */
    111    public String getAttributeName()
    112    {
    113        return attributeName;
    114    }
    115
    116    /**
    117     * Returns a flag whether this is a result of type attribute. If result is
    118     * <b>true</b>, the attribute name and value can be queried. Otherwise, only
    119     * the result node is available.
    120     *
    121     * @return <b>true</b> for an attribute result, <b>false</b> otherwise
    122     */
    123    public boolean isAttributeResult()
    124    {
    125        return StringUtils.isNotEmpty(getAttributeName());
    126    }
    127
    128    /**
    129     * Returns the attribute value if this is an attribute result. If this is
    130     * not an attribute result, an exception is thrown.
    131     *
    132     * @param handler the {@code NodeHandler}
    133     * @return the attribute value
    134     * @throws IllegalStateException if this is not an attribute result
    135     */
    136    public Object getAttributeValue(final NodeHandler<T> handler)
    137    {
    138        if (!isAttributeResult())
    139        {
    140            throw new IllegalStateException("This is not an attribute result! "
    141                    + "Attribute value cannot be fetched.");
    142        }
    143        return handler.getAttributeValue(getNode(), getAttributeName());
    144    }
    145
    146    @Override
    147    public int hashCode()
    148    {
    149        return new HashCodeBuilder().append(getNode())
    150                .append(getAttributeName()).toHashCode();
    151    }
    152
    153    /**
    154     * Compares this object with another one. Two instances of
    155     * {@code QueryResult} are considered equal if they are of the same result
    156     * type and have the same properties.
    157     *
    158     * @param obj the object to compare to
    159     * @return a flag whether these objects are equal
    160     */
    161    @Override
    162    public boolean equals(final Object obj)
    163    {
    164        if (this == obj)
    165        {
    166            return true;
    167        }
    168        if (!(obj instanceof QueryResult))
    169        {
    170            return false;
    171        }
    172
    173        final QueryResult<?> c = (QueryResult<?>) obj;
    174        return new EqualsBuilder().append(getNode(), c.getNode())
    175                .append(getAttributeName(), c.getAttributeName()).isEquals();
    176    }
    177
    178    /**
    179     * Returns a string representation of this object. Depending on the result
    180     * type either the result node or the parent node and the attribute name are
    181     * contained in this string.
    182     *
    183     * @return a string for this object
    184     */
    185    @Override
    186    public String toString()
    187    {
    188        final ToStringBuilder sb = new ToStringBuilder(this);
    189        if (isAttributeResult())
    190        {
    191            sb.append("parentNode", getNode()).append("attribute",
    192                    getAttributeName());
    193        }
    194        else
    195        {
    196            sb.append("resultNode", getNode());
    197        }
    198        return sb.toString();
    199    }
    200}