How to create custom exception handler in CakePHP?

CakePHP is a popular PHP framework that allows you to quickly build web applications. Various exceptions can occur while processing user input and performing tasks such as database operations. How can exceptions be handled so that an error message is not presented directly to the user when a problem occurs? This is where custom exception handlers come in. In this article, we will explore how to create custom exception handlers in CakePHP.

Why do we need custom exception handlers?

When a web application throws an exception, CakePHP displays a standard exception error page related to the application. By default, these pages include stack traces, exception messages, and other contextual information that may be present. Although this is very useful for developers, in a production environment, we cannot present such error messages to users. Instead, we must provide custom exception pages to ensure your application can function properly and protect your data and user privacy information.

Creating a custom exception handler in CakePHP

To create a custom exception handler, we will use CakePHP’s exception class. This is a general base class that provides many properties and methods for managing exceptions. We will create a subclass that extends the CakePHPExceptionRenderer class. Here are the steps to accomplish this:

1. Create a custom exception class

We will create an exception class called AppException that Will serve as the base class for all exceptions in our application. We'll add some default properties and methods in there to make sure all exceptions meet our requirements. Our custom exception class should look like the following example:

<?php
namespace AppError;

use CakeCoreExceptionException;

class AppException extends Exception
{
    protected $_messageTemplate = 'An error occurred.';
    protected $_defaultCode = 500;

    public function __construct($message = null, $code = null, $previous = null)
    {
        if (empty($message)) {
            $message = $this->_messageTemplate;
        }

        if (empty($code)) {
            $code = $this->_defaultCode;
        }

        parent::__construct($message, $code, $previous);
    }

    public function getResponse()
    {
        // your custom response handling logic here
    }
}

2. Create AppExceptionRendererClass

Now we will create a new exception renderer class, and extends the CakeErrorExceptionRenderer class. In this class we will define which template will be used in which exception case. We can choose to define different exceptions in this class, such as HTTP 404 errors, internal server errors, etc. Here is an example AppExceptionRenderer class:

<?php 
.namespace AppError;

use CakeErrorExceptionRenderer;
use Throwable;

class AppExceptionRenderer extends ExceptionRenderer {

    public function render() {
        $exception = $this->error instanceof Throwable ? $this->error : new FatalErrorException($this->error->getMessage(), 0, E_ERROR, __FILE__, __LINE__);
        
        $this->controller->response = $this->_getJsonResponse($exception);
        
        $this->controller->response->statusCode($exception->getCode());
        
    }
    
    protected function _getJsonResponse(Throwable $exception): JsonResponse {
        $response = new JsonResponse([
            'status' => 'error',
            'code' => $exception->getCode(),
            'message' => $exception->getMessage(),
        ],JsonResponse::HTTP_OK);
        
        if (method_exists($exception, 'getResponse')) {
            $response = $exception->getResponse();
        }
        
        return $response;
    }
}

This class will catch exceptions and render a custom template while the application is running. You can define required logic in this class, such as unconventional exception receivers, custom page rendering, etc.

3. Configuring the exception handler

Now that we have defined all the necessary classes, we need to tell the application to use these classes when catching exceptions. We will use the Error section of CakePHP’s configuration file config/app.php. Change the following settings to tell the framework to use our custom exception handler:

'Error' => [
        'errorLevel' => E_ALL & ~E_USER_DEPRECATED,
        'exceptionRenderer' => 'AppErrorAppExceptionRenderer',
    ],

This will tell CakePHP to use our custom exception handler when an exception is thrown while the application is running.

Summary

Creating custom exception handlers in CakePHP requires some extra work, but the results are worth it. By using custom exception handlers, we can protect our application and user data while ensuring that the application still functions properly when an error occurs. The steps mentioned above are just a basic way to show how to customize the exception handler, you can change and extend it as needed according to the actual situation.

I hope this article will help you. If you have any questions or comments, please ask in the comments section below. Thank you for reading!

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