# ExceptionHandler

**Kind:** Class

**Source:** [`packages/core/errors/exception-handler.ts`](https://github.com/nestjs/nest/blob/master/packages/core/errors/exception-handler.ts#L3)

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

`ExceptionHandler` centralizes application error handling within the core error layer. Its `handle()` method receives an exception, applies the project's error-handling policy, and translates it into the appropriate logging, response, or propagation behavior for the calling layer.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `handle` | `handle(exception: Error)` | `void` |

## Diagram

```mermaid
graph LR
  A[Application Code] -->|throws or catches error| B[ExceptionHandler]
  B -->|handle(error)| C{Classify Exception}
  C --> D[Log / Report Error]
  C --> E[Create Standardized Error Result]
  E --> F[API, Worker, or Caller]
```

## Usage

```ts
import { ExceptionHandler } from "@your-project/core/errors/exception-handler";

const exceptionHandler = new ExceptionHandler();

try {
  await processOrder(orderId);
} catch (error) {
  return exceptionHandler.handle(error);
}
```

## AI Coding Instructions

- Route caught application errors through `ExceptionHandler.handle()` instead of duplicating error-formatting logic in controllers, services, or jobs.
- Preserve the original error when passing it to `handle()`; avoid replacing it with a generic message before the handler can classify it.
- Keep domain-specific validation and business errors distinguishable from unexpected infrastructure errors so the handler can apply the correct response policy.
- Ensure new execution entry points, such as HTTP handlers, queue consumers, and CLI commands, integrate with this centralized error-handling path.

## Relationships

- IMPORTS → `Logger`