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NestJS Enterprise Backend APIs · Aula

Tratamento de Erros e Interceptadores

Implemente filtros de exceção personalizados para tratar erros de forma adequada e use interceptadores para transformar respostas ou registrar requisições.

Tratamento de Erros e Interceptadores é uma aula grátis de NestJS Enterprise Backend APIs no CoddyKit. Esta é a aula 3 de 3. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de NestJS Enterprise Backend APIs, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de NestJS Enterprise Backend APIs inclui 3 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Graceful API Error Handling

When building APIs, it's crucial to handle errors gracefully. Instead of crashing or returning vague messages, your API should provide clear, consistent feedback to clients.

This makes your API user-friendly and helps in debugging both client-side and server-side issues.

NestJS Built-in Exceptions

NestJS provides a set of standard HTTP exceptions, extending from HttpException. These exceptions map directly to common HTTP status codes.

  • BadRequestException (400)
  • UnauthorizedException (401)
  • NotFoundException (404)
  • InternalServerErrorException (500)

Using these ensures your API speaks the standard HTTP language.

Throwing Built-in Exceptions

You can throw these exceptions directly from your controllers or services. NestJS's built-in exception layer will catch them and automatically format a standardized JSON error response.

Try running this example and access /greet/World (success) and /greet/error (error) to see the difference:

import { NestFactory } from '@nestjs/core';
import { Controller, Get, Param, NotFoundException, Module } from '@nestjs/common';

@Controller('greet')
class GreetController {
  @Get(':name')
  hello(@Param('name') name: string) {
    if (name === 'error') {
      throw new NotFoundException('Name "error" is not allowed!');
    }
    return `Hello, ${name}!`;
  }
}

@Module({
  controllers: [GreetController],
})
class AppModule {}

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  await app.listen(3000);
  console.log('App running on http://localhost:3000');
  console.log('Try http://localhost:3000/greet/World');
  console.log('Try http://localhost:3000/greet/error');
}
bootstrap();

Custom Exception Filters

While built-in exceptions are useful, you might need more control over the error response format. This is where custom exception filters come in.

A custom filter lets you catch specific exceptions (or all exceptions) and define exactly what response is sent back to the client, including custom logging or integration with external services.

Building a Custom Filter

To create a custom filter, you implement the ExceptionFilter interface and decorate it with @Catch(), specifying the exception type(s) it should handle. Here's a basic example:

import { ExceptionFilter, Catch, ArgumentsHost, HttpException, HttpStatus } from '@nestjs/common';
import { Request, Response } from 'express';

@Catch(HttpException)
export class CustomHttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse<Response>();
    const request = ctx.getRequest<Request>();
    const status = exception.getStatus();

    response
      .status(status)
      .json({
        statusCode: status,
        timestamp: new Date().toISOString(),
        path: request.url,
        customMessage: `An error occurred: ${exception.message}`,
      });
  }
}

Applying Custom Filters

Once created, a custom filter needs to be applied. You can apply filters:

  • Globally: Using app.useGlobalFilters(new MyFilter()) in main.ts.
  • Controller-scoped: Using @UseFilters(MyFilter) on a controller class.
  • Method-scoped: Using @UseFilters(MyFilter) on a specific route handler method.

Global filters catch exceptions across your entire application, providing a consistent error structure.

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module'; // Assume AppModule exists
import { CustomHttpExceptionFilter } from './custom-http-exception.filter'; // Assume filter exists

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  app.useGlobalFilters(new CustomHttpExceptionFilter());
  await app.listen(3000);
}

Introducing Interceptors

Interceptors are another powerful feature in NestJS, inspired by Aspect-Oriented Programming (AOP). They allow you to 'intercept' requests and responses, adding extra logic before or after a route handler executes.

Think of them as hooks into the request-response lifecycle, giving you fine-grained control.

Common Interceptor Uses

Interceptors are incredibly versatile and can be used for various purposes:

  • Logging: Log request details, execution time, and responses.
  • Transforming responses: Modify the outgoing data structure (e.g., wrap in a data object).
  • Caching: Implement response caching for performance.
  • Binding extra logic: Execute code before/after a method.

Logging Interceptor Example

Here's a simple interceptor that logs the time taken for a request to complete. It uses RxJS operators like tap and finalize to interact with the observable stream.

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { tap, finalize } from 'rxjs/operators';

@Injectable()
export class LoggingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    console.log('Before request...');

    const now = Date.now();
    return next.handle().pipe(
      tap(() => console.log(`After request... ${Date.now() - now}ms`)),
      finalize(() => console.log('Request/response cycle finalized.'))
    );
  }
}

Transforming Responses

Interceptors can also transform the data returned by your route handlers. This is common for standardizing API responses, for example, by wrapping all successful data in a data property to ensure consistency.

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

interface Response<T> {
  data: T;
}

@Injectable()
export class TransformInterceptor<T> implements NestInterceptor<T, Response<T>> {
  intercept(context: ExecutionContext, next: CallHandler): Observable<Response<T>> {
    return next.handle().pipe(map(data => ({ data })));
  }
}

Quick Check: Error vs Intercept

You've learned about both Exception Filters and Interceptors. Let's test your understanding of their primary roles.

Recap & Next Steps

In this lesson, we covered essential techniques for building robust NestJS APIs:

  • Graceful Error Handling using built-in HTTP exceptions.
  • Custom Exception Filters to customize error responses and handle specific exceptions.
  • Interceptors for logging, transforming responses, and adding cross-cutting concerns.

Mastering these concepts will help you build professional, maintainable, and user-friendly APIs.

Perguntas Frequentes

A aula “Tratamento de Erros e Interceptadores” é grátis?

Sim — o texto completo de “Tratamento de Erros e Interceptadores” é grátis para ler aqui na web. Para praticá-la interativamente (um editor de código integrado e um tutor de IA 24/7) e desbloquear o restante do curso de NestJS Enterprise Backend APIs, atualize para CoddyKit PRO. O curso de NestJS Enterprise Backend APIs inclui 3 aulas no total.

O que vou aprender em “Tratamento de Erros e Interceptadores”?

Implemente filtros de exceção personalizados para tratar erros de forma adequada e use interceptadores para transformar respostas ou registrar requisições. Você pratica NestJS Enterprise Backend APIs com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

Preciso ter experiência prévia para começar NestJS Enterprise Backend APIs?

Nenhuma experiência prévia é necessária. NestJS Enterprise Backend APIs no CoddyKit é estruturado para alunos iniciantes até avançados, então você pode começar aqui ou desde o início e aprender no seu ritmo. Esta é a aula 3 de 3.

Quanto tempo leva a aula “Tratamento de Erros e Interceptadores”?

A maioria das aulas CoddyKit leva cerca de 5–10 minutos. Cada uma é compacta e interativa, então você faz progresso constante e retoma exatamente de onde parou entre web e app.

Posso escrever e executar código nesta aula de NestJS Enterprise Backend APIs?

Sim. Cada aula de NestJS Enterprise Backend APIs inclui um editor de código integrado, então você escreve e executa código real direto no navegador e recebe feedback de IA instantaneamente — nenhuma configuração local necessária.

Todas as aulas deste curso

  1. Rotas e Tratamento de Requisições
  2. Operações CRUD com TypeORM
  3. Tratamento de Erros e Interceptadores
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