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 */
017
018package org.apache.logging.log4j.core.config.plugins.visitors;
019
020import java.lang.annotation.Annotation;
021import java.lang.reflect.Member;
022
023import org.apache.logging.log4j.core.LogEvent;
024import org.apache.logging.log4j.core.config.Configuration;
025import org.apache.logging.log4j.core.config.Node;
026import org.apache.logging.log4j.core.lookup.StrSubstitutor;
027
028/**
029 * Visitor strategy for parsing data from a {@link Node}, doing any relevant type conversion, and returning a
030 * parsed value for that variable. Implementations must be constructable using the default constructor.
031 *
032 * @param <A> the Annotation type.
033 */
034public interface PluginVisitor<A extends Annotation> {
035
036    /**
037     * Sets the Annotation to be used for this. If the given Annotation is not compatible with this class's type, then
038     * it is ignored.
039     *
040     * @param annotation the Annotation instance.
041     * @return {@code this}.
042     * @throws NullPointerException if the argument is {@code null}.
043     */
044    PluginVisitor<A> setAnnotation(Annotation annotation);
045
046    /**
047     * Sets the list of aliases to use for this visit. No aliases are required, however.
048     *
049     * @param aliases the list of aliases to use.
050     * @return {@code this}.
051     */
052    PluginVisitor<A> setAliases(String... aliases);
053
054    /**
055     * Sets the class to convert the plugin value to on this visit. This should correspond with a class obtained from
056     * a factory method or builder class field. Not all PluginVisitor implementations may need this value.
057     *
058     * @param conversionType the type to convert the plugin string to (if applicable).
059     * @return {@code this}.
060     * @throws NullPointerException if the argument is {@code null}.
061     */
062    PluginVisitor<A> setConversionType(Class<?> conversionType);
063
064    /**
065     * Sets the StrSubstitutor to use for converting raw strings before type conversion. Generally obtained from a
066     * {@link org.apache.logging.log4j.core.config.Configuration}.
067     *
068     * @param substitutor the StrSubstitutor to use on plugin values.
069     * @return {@code this}.
070     * @throws NullPointerException if the argument is {@code null}.
071     */
072    PluginVisitor<A> setStrSubstitutor(StrSubstitutor substitutor);
073
074    /**
075     * Sets the Member that this visitor is being used for injection upon. For instance, this could be the Field
076     * that is being used for injecting a value, or it could be the factory method being used to inject parameters
077     * into.
078     *
079     * @param member the member this visitor is parsing a value for.
080     * @return {@code this}.
081     */
082    PluginVisitor<A> setMember(Member member);
083
084    /**
085     * Visits a Node to obtain a value for constructing a Plugin object.
086     *
087     * @param configuration the current Configuration.
088     * @param node          the current Node corresponding to the Plugin object being created.
089     * @param event         the current LogEvent that caused this Plugin object to be made (optional).
090     * @param log           the StringBuilder being used to build a debug message.
091     * @return the converted value to be used for Plugin creation.
092     */
093    Object visit(Configuration configuration, Node node, LogEvent event, StringBuilder log);
094}