# NestApplication

**Kind:** Class

**Source:** [`packages/core/nest-application.ts`](https://github.com/nestjs/nest/blob/master/packages/core/nest-application.ts#L54)

**Part of:** [Core](subsystem-packages-core)

`NestApplication` is the core runtime class behind a Nest HTTP application. It coordinates HTTP server creation, module registration, WebSocket integration, parser middleware, and application lifecycle initialization. Applications are typically created through `NestFactory`, which configures and returns a `NestApplication` instance.

**Extends:** `NestApplicationContext`

**Implements:** `INestApplication`

## Methods

| Method | Signature | Returns |
|---|---|---|
| `dispose` | `dispose()` | `Promise<void>` |
| `getHttpAdapter` | `getHttpAdapter()` | `AbstractHttpAdapter` |
| `registerHttpServer` | `registerHttpServer()` | `void` |
| `getUnderlyingHttpServer` | `getUnderlyingHttpServer()` | `T` |
| `applyOptions` | `applyOptions()` | `void` |
| `createServer` | `createServer()` | `T` |
| `registerModules` | `registerModules()` | `void` |
| `registerWsModule` | `registerWsModule()` | `void` |
| `init` | `init()` | `Promise<this>` |
| `registerParserMiddleware` | `registerParserMiddleware()` | `void` |
| `registerRouter` | `registerRouter()` | `void` |
| `registerRouterHooks` | `registerRouterHooks()` | `void` |
| `connectMicroservice` | `connectMicroservice(microserviceOptions: T, hybridAppOptions: NestHybridApplicationOptions)` | `INestMicroservice` |
| `getMicroservices` | `getMicroservices()` | `INestMicroservice[]` |
| `getHttpServer` | `getHttpServer()` | `void` |
| `startAllMicroservices` | `startAllMicroservices()` | `Promise<this>` |
| `use` | `use(args: [any, any?])` | `this` |
| `useBodyParser` | `useBodyParser(args: [any, any?])` | `this` |
| `enableCors` | `enableCors(options: any)` | `void` |
| `enableVersioning` | `enableVersioning(options: VersioningOptions)` | `this` |
| `listen` | `listen(port: number | string)` | `Promise<any>` |
| `listen` | `listen(port: number | string, hostname: string)` | `Promise<any>` |
| `listen` | `listen(port: number | string, args: any[])` | `Promise<any>` |
| `getUrl` | `getUrl()` | `Promise<string>` |
| `setGlobalPrefix` | `setGlobalPrefix(prefix: string, options: GlobalPrefixOptions)` | `this` |
| `useWebSocketAdapter` | `useWebSocketAdapter(adapter: WebSocketAdapter)` | `this` |
| `useGlobalFilters` | `useGlobalFilters(filters: ExceptionFilter[])` | `this` |
| `useGlobalPipes` | `useGlobalPipes(pipes: PipeTransform<any>[])` | `this` |
| `useGlobalInterceptors` | `useGlobalInterceptors(interceptors: NestInterceptor[])` | `this` |
| `useGlobalGuards` | `useGlobalGuards(guards: CanActivate[])` | `this` |
| `useStaticAssets` | `useStaticAssets(options: any)` | `this` |
| `useStaticAssets` | `useStaticAssets(path: string, options: any)` | `this` |
| `useStaticAssets` | `useStaticAssets(pathOrOptions: any, options: any)` | `this` |
| `setBaseViewsDir` | `setBaseViewsDir(path: string | string[])` | `this` |
| `setViewEngine` | `setViewEngine(engineOrOptions: any)` | `this` |

## Properties

| Property | Type |
|---|---|
| `logger` | `any` |

## Where it refuses work

- `NestApplication` stops the work with an early return when `!this.appOptions || !this.appOptions.cors`.
- `NestApplication` stops the work with an early return when `!passCustomOptions`.
- `NestApplication` stops the work with an early return when `!this.socketModule`.
- `NestApplication` stops the work with an early return when `this.isInitialized`.
- `NestApplication` stops the work with an early return when `originalCallbackArgs[0] instanceof Error`.
- `NestApplication` stops the work with an early return when `platform() === 'win32'`.

## Diagram

```mermaid
graph LR
  A[NestFactory.create()] --> B[NestApplication]
  B --> C[createServer()]
  B --> D[registerModules()]
  B --> E[registerWsModule()]
  B --> F[registerParserMiddleware()]
  B --> G[init()]
  G --> H[HTTP Adapter]
  H --> I[Underlying HTTP Server]
  B --> J[dispose()]
```

## Usage

```ts
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);

  // Initialize registered modules, middleware, and adapters.
  await app.init();

  const httpAdapter = app.getHttpAdapter();
  const server = app.getUnderlyingHttpServer();

  console.log(`Using adapter: ${httpAdapter.getType()}`);
  console.log(`Server available: ${Boolean(server)}`);

  await app.listen(3000);

  process.on('SIGTERM', async () => {
    await app.close();
    await app.dispose();
  });
}

bootstrap();
```

## AI Coding Instructions

- Create application instances through `NestFactory.create()` rather than constructing `NestApplication` directly.
- Preserve the initialization order: register modules and infrastructure before calling `init()`.
- Use `getHttpAdapter()` for adapter-specific integrations; avoid assuming Express or Fastify APIs are always available.
- Use `getUnderlyingHttpServer()` only when direct access to the native HTTP server is required.
- Ensure shutdown paths clean up resources through the application lifecycle, including disposal when appropriate.

## Relationships

- IMPORTS → `CanActivate`
- IMPORTS → `ExceptionFilter`
- IMPORTS → `HttpServer`
- IMPORTS → `INestApplication`
- IMPORTS → `INestMicroservice`
- IMPORTS → `NestHybridApplicationOptions`
- IMPORTS → `NestInterceptor`
- IMPORTS → `PipeTransform`
- IMPORTS → `VersioningOptions`
- IMPORTS → `VersioningType`
- IMPORTS → `WebSocketAdapter`
- IMPORTS → `GlobalPrefixOptions`
- IMPORTS → `NestApplicationOptions`
- IMPORTS → `Logger`
- IMPORTS → `loadPackage`
- IMPORTS → `addLeadingSlash`
- IMPORTS → `isFunction`
- IMPORTS → `isObject`
- IMPORTS → `isString`
- IMPORTS → `SocketModule`
- IMPORTS → `MicroservicesModule`
- IMPORTS → `-nestjs-microservices`

## Used by

2 references from 2 files. Each is a place in this repository where the symbol is actually used — go read one rather than trusting an example.

### Imported by (2)

- `TestingModule` — `packages/testing/testing-module.ts`:26
- `BaseWsInstance` — `packages/websockets/adapters/ws-adapter.ts`:8