feat(@nestjs/core): Add init function on NestApplicationContext to API

packages/common/interfaces/nest-application-context.interface.ts

@@ -29,4 +29,12 @@ export interface INestApplicationContext {
    * @returns {void}
    */
   useLogger(logger: LoggerService);
+
+  /**
+   * Initalizes the Nest application.
+   * Calls the Nest lifecycle events.
+   *
+   * @returns {Promise<this>} The NestApplicationContext instance as Promise
+   */
+  init(): Promise<this>;
 }

packages/core/nest-application-context.ts

@@ -19,6 +19,7 @@ import { ModuleTokenFactory } from './injector/module-token-factory';
 export class NestApplicationContext implements INestApplicationContext {
   private readonly moduleTokenFactory = new ModuleTokenFactory();
   private readonly containerScanner: ContainerScanner;
+  protected isInitialized: boolean = false;
 
   constructor(
     protected readonly container: NestContainer,
@@ -59,9 +60,20 @@ export class NestApplicationContext implements INestApplicationContext {
     );
   }
 
+  /**
+   * Initalizes the Nest application.
+   * Calls the Nest lifecycle events.
+   *
+   * @returns {Promise<this>} The NestApplicationContext instance as Promise
+   */
   public async init(): Promise<this> {
+    // Ignore if is already initialized
+    if (this.isInitialized) return;
+
     await this.callInitHook();
     await this.callBootstrapHook();
+
+    this.isInitialized = true;
     return this;
   }
 

packages/core/nest-application.ts

@@ -59,7 +59,6 @@ export class NestApplication extends NestApplicationContext
   private readonly routesResolver: Resolver;
   private readonly microservices = [];
   private httpServer: http.Server;
-  private isInitialized = false;
 
   constructor(
     container: NestContainer,

packages/microservices/nest-microservice.ts

@@ -32,7 +32,6 @@ export class NestMicroservice extends NestApplicationContext
   private microserviceConfig: MicroserviceOptions;
   private server: Server & CustomTransportStrategy;
   private isTerminated = false;
-  private isInitialized = false;
   private isInitHookCalled = false;
 
   constructor(