# MiddlewareResolver

**Kind:** Class

**Source:** [`packages/core/middleware/resolver.ts`](https://github.com/nestjs/nest/blob/master/packages/core/middleware/resolver.ts#L7)

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

`MiddlewareResolver` resolves configured middleware definitions into runtime middleware instances. It centralizes middleware instantiation so the application pipeline can execute middleware consistently and with the appropriate dependencies.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `resolveInstances` | `resolveInstances(moduleRef: Module, moduleName: string)` | `void` |

## Diagram

```mermaid
graph LR
  A[Middleware Configuration] --> B[MiddlewareResolver]
  B --> C[Resolve Middleware Instances]
  C --> D[Application Middleware Pipeline]
  D --> E[Request / Response Handling]
```

## Usage

```ts
import { MiddlewareResolver } from "@your-package/core";

// In most applications, the resolver is created or provided by the core runtime.
function configureMiddleware(resolver: MiddlewareResolver) {
  const middlewareInstances = resolver.resolveInstances();

  // Register the resolved middleware with the application's request pipeline.
  middlewareInstances.forEach((middleware) => {
    app.use(middleware);
  });
}
```

## AI Coding Instructions

- Use `resolveInstances()` as the single integration point for converting configured middleware into executable runtime instances.
- Keep middleware registration order intact; middleware behavior often depends on its position in the request pipeline.
- Ensure middleware dependencies are registered in the application's container before resolving instances.
- Avoid manually instantiating middleware when the resolver is available, as this can bypass dependency injection or lifecycle handling.