本篇學習筆記來不及趕完，只好先上傳之後再改了......

Exception filter

Exception

• 標準(Standard)Exception:

import { Controller, Get, HttpException, HttpStatus } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get()
  getHello(): string {
    throw new HttpException('發生錯誤！',HttpStatus.BAD_REQUEST)
    return this.appService.getHello();
  }
}

Api測試結果：

• 自訂(Custom)Exception:

自定義回傳格式：

import { Controller, Get, HttpException, HttpStatus } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get()
  getHello(): string {
    const obj={
      code:HttpStatus.BAD_REQUEST,
      message:'發生錯誤！'
    }
    throw new HttpException(obj,HttpStatus.BAD_REQUEST)
    return this.appService.getHello();
  }
}

api測試結果：

• 內建(Built-in)Http Exception:

內建回傳格式：

import { BadRequestException, Controller, Get, HttpException, HttpStatus } from '@nestjs/common';
import { AppService } from './app.service';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Get()
  getHello(): string {
    throw new BadRequestException('發生錯誤！');
    return this.appService.getHello();
  }
}

api測試結果：

自訂Exception filter

import { ArgumentsHost, Catch, ExceptionFilter, HttpException } from '@nestjs/common';

@Catch(HttpException)
export class HttpFilter<T extends HttpException> implements ExceptionFilter<T> {
  catch(exception: T, host: ArgumentsHost) {}
}

解釋說明：

1. 使用catch( )方法，裡面有兩個變數，exception和host．第一個T代表被捕捉到exception，因為無法確認是什麼類型，所以是這個T是泛型

ArguementsHost

ArguementsHost是一個helper class，我們可以透過它來獲得一些跟該請求相關的參數，比如request、response物件等等的，再來也可以為不同的底層參數做封裝．
關於host可使用的方法，官網有特別寫在這邊https://docs.nestjs.com/fundamentals/execution-context#execution-context