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}