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 * @version $Id: QueryResult.java 1790899 2017-04-10 21:56:46Z ggregory $
042 * @since 2.0
043 * @param <T> the type of the result nodes
044 */
045public final class QueryResult<T>
046{
047    /** The node result. */
048    private final T node;
049
050    /** The name of the result attribute. */
051    private final String attributeName;
052
053    /**
054     * Creates a new instance of {@code QueryResult}.
055     *
056     * @param nd the node
057     * @param attr the attribute name
058     */
059    private QueryResult(T nd, String attr)
060    {
061        node = nd;
062        attributeName = attr;
063    }
064
065    /**
066     * Creates a {@code QueryResult} instance representing the specified result
067     * node.
068     *
069     * @param <T> the type of the result node
070     * @param resultNode the result node
071     * @return the newly created instance
072     */
073    public static <T> QueryResult<T> createNodeResult(T resultNode)
074    {
075        return new QueryResult<>(resultNode, null);
076    }
077
078    /**
079     * Creates a {@code QueryResult} instance representing an attribute result.
080     * An attribute result consists of the node the attribute belongs to and the
081     * attribute name. (The value can be obtained based on this information.)
082     *
083     * @param parentNode the node which owns the attribute
084     * @param attrName the attribute name
085     * @param <T> the type of the parent node
086     * @return the newly created instance
087     */
088    public static <T> QueryResult<T> createAttributeResult(T parentNode,
089                                                           String attrName)
090    {
091        return new QueryResult<>(parentNode, attrName);
092    }
093
094    /**
095     * Returns the node referenced by this object. Depending on the result type,
096     * this is either the result node or the parent node of the represented
097     * attribute.
098     *
099     * @return the referenced node
100     */
101    public T getNode()
102    {
103        return node;
104    }
105
106    /**
107     * Returns the name of the attribute. This method is defined only for
108     * results of type attribute.
109     *
110     * @return the attribute name
111     */
112    public String getAttributeName()
113    {
114        return attributeName;
115    }
116
117    /**
118     * Returns a flag whether this is a result of type attribute. If result is
119     * <b>true</b>, the attribute name and value can be queried. Otherwise, only
120     * the result node is available.
121     *
122     * @return <b>true</b> for an attribute result, <b>false</b> otherwise
123     */
124    public boolean isAttributeResult()
125    {
126        return StringUtils.isNotEmpty(getAttributeName());
127    }
128
129    /**
130     * Returns the attribute value if this is an attribute result. If this is
131     * not an attribute result, an exception is thrown.
132     *
133     * @param handler the {@code NodeHandler}
134     * @return the attribute value
135     * @throws IllegalStateException if this is not an attribute result
136     */
137    public Object getAttributeValue(NodeHandler<T> handler)
138    {
139        if (!isAttributeResult())
140        {
141            throw new IllegalStateException("This is not an attribute result! "
142                    + "Attribute value cannot be fetched.");
143        }
144        return handler.getAttributeValue(getNode(), getAttributeName());
145    }
146
147    @Override
148    public int hashCode()
149    {
150        return new HashCodeBuilder().append(getNode())
151                .append(getAttributeName()).toHashCode();
152    }
153
154    /**
155     * Compares this object with another one. Two instances of
156     * {@code QueryResult} are considered equal if they are of the same result
157     * type and have the same properties.
158     *
159     * @param obj the object to compare to
160     * @return a flag whether these objects are equal
161     */
162    @Override
163    public boolean equals(Object obj)
164    {
165        if (this == obj)
166        {
167            return true;
168        }
169        if (!(obj instanceof QueryResult))
170        {
171            return false;
172        }
173
174        QueryResult<?> c = (QueryResult<?>) obj;
175        return new EqualsBuilder().append(getNode(), c.getNode())
176                .append(getAttributeName(), c.getAttributeName()).isEquals();
177    }
178
179    /**
180     * Returns a string representation of this object. Depending on the result
181     * type either the result node or the parent node and the attribute name are
182     * contained in this string.
183     *
184     * @return a string for this object
185     */
186    @Override
187    public String toString()
188    {
189        ToStringBuilder sb = new ToStringBuilder(this);
190        if (isAttributeResult())
191        {
192            sb.append("parentNode", getNode()).append("attribute",
193                    getAttributeName());
194        }
195        else
196        {
197            sb.append("resultNode", getNode());
198        }
199        return sb.toString();
200    }
201}