> For the complete documentation index, see [llms.txt](https://docs.nestjstools.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.nestjstools.com/getting-started/message-handler.md).

# Message Handler

## 💬 Defining a Message & Message Handler

Messages are the core units of communication in your system. Each message can have a dedicated handler that processes it when received. This section explains how to define a **message** and implement a **handler**.

***

### 📨 Define Your Message

A message is a simple class representing the data being sent between services or components:

```ts
// send-message.ts
export class SendMessage {
  constructor(
    public readonly content: string,
  ) {}
}
```

This message can now be published on a bus and handled by one or more consumers.

***

### 🛠️ Define a Message Handler

Handlers process incoming messages. They must implement the `IMessageHandler<T>` interface.

```ts
import { Injectable } from '@nestjs/common';
import { MessageHandler, IMessageHandler, MessageResponse } from '@nestjstools/messaging';
import { SendMessage } from './send-message';

@Injectable()
@MessageHandler('your.message') // This should match the message route you publish to
export class SendMessageHandler implements IMessageHandler<SendMessage> {
  async handle(message: SendMessage): Promise<MessageResponse | void> {
    console.log(message.content);
    // Add your business logic here
  }
}
```

***

### 🔁 Multiple Routes

{% hint style="info" %}
You can associate a single handler with **multiple message routes**:

```ts
@MessageHandler('your.message', 'your.message2')
```

{% endhint %}

***

### Optional: Use `@DenormalizeMessage()` Decorator

If you want NestJS to automatically instantiate the incoming message as a proper `class` (rather than just receiving raw JSON), use the `@DenormalizeMessage()` decorator:

```ts
async handle(@DenormalizeMessage() message: SendMessage): Promise<MessageResponse | void> {
  // message is a real SendMessage instance
}
```


---

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