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