# RoutesResolver

**Kind:** Class

**Source:** [`packages/core/router/routes-resolver.ts`](https://github.com/nestjs/nest/blob/master/packages/core/router/routes-resolver.ts#L35)

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

`RoutesResolver` connects discovered controllers and route metadata to the underlying HTTP adapter during application initialization. It registers controller routes, configures not-found and exception handlers, and maps framework exceptions to adapter-compatible responses.

**Implements:** `Resolver`

## Methods

| Method | Signature | Returns |
|---|---|---|
| `resolve` | `resolve(applicationRef: T, globalPrefix: string)` | `void` |
| `registerRouters` | `registerRouters(routes: Map<string | symbol | Function, InstanceWrapper<Controller>>, moduleName: string, globalPrefix: string, modulePath: string, applicationRef: HttpServer)` | `void` |
| `registerNotFoundHandler` | `registerNotFoundHandler()` | `void` |
| `registerExceptionHandler` | `registerExceptionHandler()` | `void` |
| `mapExternalException` | `mapExternalException(err: any)` | `void` |

## Where it refuses work

- `RoutesResolver` stops the work with an early return when `versioningConfig`.

## Diagram

```mermaid
graph LR
  A[Application bootstrap] --> B[RoutesResolver.resolve]
  B --> C[registerRouters]
  C --> D[Controller routes]
  D --> E[HTTP adapter router]

  B --> F[registerNotFoundHandler]
  F --> E

  B --> G[registerExceptionHandler]
  G --> H[mapExternalException]
  H --> E
```

## Usage

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

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

  // RoutesResolver uses this prefix while registering controller routes.
  app.setGlobalPrefix('api');

  // During initialization, Nest internally uses RoutesResolver to:
  // - discover controller routes
  // - register them with the HTTP adapter
  // - configure 404 and exception handlers
  await app.listen(3000);
}

bootstrap();
```

## AI Coding Instructions

- Treat `RoutesResolver` as framework bootstrap infrastructure; application code should usually define controllers and let the framework invoke `resolve()`.
- Preserve the registration order: controller routes should be registered before fallback not-found and exception handlers are attached.
- When adding route-related behavior, ensure global prefixes, module paths, and controller metadata are consistently applied.
- Keep adapter-specific error handling inside `mapExternalException()` so external HTTP adapters receive compatible error objects.
- Avoid registering catch-all routes or error middleware too early, as they can prevent resolved controller routes from being reached.

## How it works

## `RoutesResolver`

`RoutesResolver` is the HTTP-routing resolver created by `NestApplication`. During application initialization, the application invokes `resolve()` after middleware registration, then invokes its not-found and error-hook registration methods after initialization hooks. [`packages/core/nest-application.ts:190-194`](packages/core/nest-application.ts#L190-L194) [`packages/core/nest-application.ts:207-218`](packages/core/nest-application.ts#L207-L218)

It implements the `Resolver` contract: route resolution plus registration of not-found and exception handlers. [`packages/core/router/interfaces/resolver.interface.ts:1-5`](packages/core/router/interfaces/resolver.interface.ts#L1-L5)

## Relationships

- IMPORTS → `BadRequestException`
- IMPORTS → `HttpException`
- IMPORTS → `NotFoundException`
- IMPORTS → `HOST_METADATA`
- IMPORTS → `MODULE_PATH`
- IMPORTS → `VERSION_METADATA`
- IMPORTS → `Controller`
- IMPORTS → `HttpServer`
- IMPORTS → `Type`
- IMPORTS → `VersionValue`
- IMPORTS → `Logger`