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.juneau.rest.server;
018
019import static java.lang.annotation.ElementType.*;
020import static java.lang.annotation.RetentionPolicy.*;
021
022import java.lang.annotation.*;
023
024import org.apache.juneau.commons.inject.*;
025
026import jakarta.servlet.*;
027
028/**
029 * Identifies a method that gets called during servlet initialization.
030 *
031 * <p>
032 * This method is called from within the {@link Servlet#init(ServletConfig)} method after the
033 * resource's annotation-driven configuration has been applied to the in-flight {@link RestContext}, but before
034 * any HTTP request is dispatched. It's the supported hook for one-time setup work such as loading data files
035 * or precomputing caches.
036 *
037 * <p>
038 * Method parameters are resolved from the
039 * {@link BeanStore bean store} the same way as any other Juneau-injected
040 * method. {@link jakarta.servlet.ServletConfig}, {@link jakarta.servlet.ServletContext}, the resource instance
041 * itself, and any bean registered via {@link Bean @Bean} or the
042 * configured bean-store hooks are all resolvable. Zero-argument variants are also supported.
043 *
044 * <p>
045 * <b>Note (10.0):</b> two related Builder-injection protocols have been removed in this release. They had zero
046 * real-world callers across the codebase before deletion:
047 * <ul>
048 *    <li><b>Per-operation:</b> {@code @RestInit public void init(RestOpContext.Builder b)} (invoked once per
049 *       <code>@RestOp</code>-annotated method) — replaced by declarative <code>@RestOp(...)</code> attributes,
050 *       <code>@Bean(name=, methodScope=)</code>-named beans, or class-level <code>@RestInit</code> hooks.
051 *    <li><b>Class-level Builder injection:</b> {@code @RestInit public void init(RestContext.Builder b)} (which
052 *       injected the in-flight resource-level builder so the hook could imperatively mutate it) — replaced by the
053 *       same declarative surfaces. Migrate by moving each <code>builder.xxx(...)</code> call to the equivalent
054 *       <code>@Rest(xxx=...)</code> annotation attribute or {@code @Bean}-named bean.
055 * </ul>
056 *
057 * <p>
058 * The remaining supported {@code @RestInit} hook shape is one whose parameters are bean-store-resolvable
059 * (no {@code RestContext.Builder} or {@code RestOpContext.Builder}). The example below uses the resource
060 * instance itself, but {@code @Bean}-supplied beans, {@code ServletConfig}, etc. work the same way.
061 *
062 * <h5 class='figure'>Example:</h5>
063 * <p class='bjava'>
064 *    <ja>@Rest</ja>(...)
065 *    <jk>public class</jk> PetStoreResource <jk>extends</jk> BasicRestServlet <jk>implements</jk> BasicUniversalJenaConfig {
066 *
067 *       <jc>// Our database.</jc>
068 *       <jk>private</jk> Map&lt;Integer,Pet&gt; <jf>petDB</jf>;
069 *
070 *       <ja>@RestInit</ja>
071 *       <jk>public void</jk> onInit() <jk>throws</jk> Exception {
072 *          <jc>// Load our database from a local JSON file.</jc>
073 *          <jf>petDB</jf> = JsonParser.<jsf>DEFAULT</jsf>.read(getClass().getResourceAsStream(<js>"PetStore.json"</js>), LinkedHashMap.<jk>class</jk>, Integer.<jk>class</jk>, Pet.<jk>class</jk>);
074 *       }
075 *    }
076 * </p>
077 *
078 * <h5 class='section'>Notes:</h5><ul>
079 *    <li class='note'>
080 *       The method should return <jk>void</jk> although if it does return any value, the value will be ignored.
081 *    <li class='note'>
082 *       The method should be <jk>public</jk> although other visibilities are valid if the security manager allows it.
083 *    <li class='note'>
084 *       Static methods can be used.
085 *    <li class='note'>
086 *       Multiple init methods can be defined on a class.
087 *       <br>Init methods on parent classes are invoked before init methods on child classes.
088 *       <br>The order of init method invocations within a class is alphabetical, then by parameter count, then by parameter types.
089 *    <li class='note'>
090 *       The method can throw any exception causing initialization of the servlet to fail.
091 *    <li class='note'>
092 *       Note that if you override a parent method, you probably need to call <code><jk>super</jk>.parentMethod(...)</code>.
093 *       <br>The method is still considered part of the parent class for ordering purposes even though it's
094 *       overridden by the child class.
095 * </ul>
096 *
097 * <h5 class='section'>See Also:</h5><ul>
098 *    <li class='link'><a class="doclink" href="https://juneau.apache.org/docs/topics/LifecycleHooks">Lifecycle Hooks</a>
099 * </ul>
100 */
101@Target({ METHOD })
102@Retention(RUNTIME)
103@Inherited
104public @interface RestInit {
105
106   /**
107    * Optional description for the exposed API.
108    *
109    * @return The annotation value.
110    * @since 9.2.0
111    */
112   String[] description() default {};
113}