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A module that is everything required to understands Druid Segments
There is a newer version: 30.0.1
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.druid.guice;

import com.google.inject.Binder;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.Provides;
import com.google.inject.TypeLiteral;
import com.google.inject.multibindings.Multibinder;
import com.google.inject.name.Names;
import org.apache.druid.java.util.common.lifecycle.Lifecycle;

import java.lang.annotation.Annotation;
import java.util.Set;

/**
 * A Module to add lifecycle management to the injector.  {@link DruidGuiceExtensions} must also be included.
 */
public class LifecycleModule implements Module
{
  /**
   * This scope includes final logging shutdown, so all other handlers in this lifecycle scope should avoid logging in
   * their stop() method, either failing silently or failing violently and throwing an exception causing an ungraceful
   * exit.
   */
  private final LifecycleScope initScope = new LifecycleScope(Lifecycle.Stage.INIT);
  private final LifecycleScope normalScope = new LifecycleScope(Lifecycle.Stage.NORMAL);
  private final LifecycleScope serverScope = new LifecycleScope(Lifecycle.Stage.SERVER);
  private final LifecycleScope annoucementsScope = new LifecycleScope(Lifecycle.Stage.ANNOUNCEMENTS);

  /**
   * Registers a class to instantiate eagerly.  Classes mentioned here will be pulled out of
   * the injector with an injector.getInstance() call when the lifecycle is created.
   *
   * Eagerly loaded classes will *not* be automatically added to the Lifecycle unless they are bound to the proper
   * scope.  That is, they are generally eagerly loaded because the loading operation will produce some beneficial
   * side-effect even if nothing actually directly depends on the instance.
   *
   * This mechanism exists to allow the {@link Lifecycle} to be the primary entry point from the injector, not to
   * auto-register things with the {@link Lifecycle}.  It is also possible to just bind things eagerly with Guice,
   * but that is almost never the correct option.  Guice eager bindings are pre-instantiated before the object graph
   * is materialized and injected, meaning that objects are not actually instantiated in dependency order.
   * Registering with the LifecyceModule, on the other hand, will instantiate the objects after the normal object
   * graph has already been instantiated, meaning that objects will be created in dependency order and this will
   * only actually instantiate something that wasn't actually depended upon.
   *
   * @param clazz the class to instantiate
   * @return this, for chaining.
   */
  public static void register(Binder binder, Class clazz)
  {
    registerKey(binder, Key.get(clazz));
  }

  /**
   * Registers a class/annotation combination to instantiate eagerly.  Classes mentioned here will be pulled out of
   * the injector with an injector.getInstance() call when the lifecycle is created.
   *
   * Eagerly loaded classes will *not* be automatically added to the Lifecycle unless they are bound to the proper
   * scope.  That is, they are generally eagerly loaded because the loading operation will produce some beneficial
   * side-effect even if nothing actually directly depends on the instance.
   *
   * This mechanism exists to allow the {@link Lifecycle} to be the primary entry point from the injector, not to
   * auto-register things with the {@link Lifecycle}.  It is also possible to just bind things eagerly with Guice,
   * but that is almost never the correct option.  Guice eager bindings are pre-instantiated before the object graph
   * is materialized and injected, meaning that objects are not actually instantiated in dependency order.
   * Registering with the LifecyceModule, on the other hand, will instantiate the objects after the normal object
   * graph has already been instantiated, meaning that objects will be created in dependency order and this will
   * only actually instantiate something that wasn't actually dependend upon.
   *
   * @param clazz the class to instantiate
   * @param annotation The annotation class to register with Guice
   * @return this, for chaining
   */
  public static void register(Binder binder, Class clazz, Class annotation)
  {
    registerKey(binder, Key.get(clazz, annotation));
  }

  /**
   * Registers a key to instantiate eagerly.  {@link Key}s mentioned here will be pulled out of
   * the injector with an injector.getInstance() call when the lifecycle is created.
   *
   * Eagerly loaded classes will *not* be automatically added to the Lifecycle unless they are bound to the proper
   * scope.  That is, they are generally eagerly loaded because the loading operation will produce some beneficial
   * side-effect even if nothing actually directly depends on the instance.
   *
   * This mechanism exists to allow the {@link Lifecycle} to be the primary entry point from the injector, not to
   * auto-register things with the {@link Lifecycle}.  It is also possible to just bind things eagerly with Guice,
   * but that is almost never the correct option.  Guice eager bindings are pre-instantiated before the object graph
   * is materialized and injected, meaning that objects are not actually instantiated in dependency order.
   * Registering with the LifecyceModule, on the other hand, will instantiate the objects after the normal object
   * graph has already been instantiated, meaning that objects will be created in dependency order and this will
   * only actually instantiate something that wasn't actually dependend upon.
   *
   * @param key The key to use in finding the DruidNode instance
   */
  public static void registerKey(Binder binder, Key key)
  {
    getEagerBinder(binder).addBinding().toInstance(new KeyHolder