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