Catching Multiple Exceptions - PHP

In this second part of a two-part series on error and exception handling in PHP, we focus specifically on handling exceptions. This article is excerpted from chapter 8 of the book Beginning PHP and Oracle: From Novice to Professional, written by W. Jason Gilmore and Bob Bryla (Apress; ISBN: 1590597702).

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By: Apress Publishing

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January 04, 2010

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Good programmers must always ensure that all possible scenarios are taken into account. Consider a scenario in which your site offers an HTML form from which the user could subscribe to a newsletter by submitting his or her e-mail address. Several outcomes are possible. For example, the user could do one of the following:

Provide a valid e-mail address
Provide an invalid e-mail address
Neglect to enter any e-mail address at all
Attempt to mount an attack such as a SQL injection

Proper exception handling will account for all such scenarios. However, you need to provide a means for catching each exception. Thankfully, this is easily possible with PHP. Listing 8-3 shows the code that satisfies this requirement.

Listing 8-3. Catching Multiple Exceptions

<?php

/* The Invalid_Email_Exception class is responsible for notifying the site
administrator in the case that the e-mail is deemed invalid. */

class Invalid_Email_Exception extends Exception {

       function __construct($message, $email) {
          $this->message = $message;
          $this->notifyAdmin($email);
       }

       private function notifyAdmin($email) {
          mail("admin@example.org","INVALID EMAIL",$email,"From:web@example.com");
       }

}

/* The Subscribe class is responsible for validating an e-mail address
and adding the user e-mail address to the database. */

class Subscribe {

function validateEmail($email) {

try {

               if ($email == "") {
                   throw new Exception("You must enter an e-mail address!");
               } else {

list($user,$domain) = explode("@", $email);

                  if (! checkdnsrr($domain, "MX"))
                      throw new Invalid_Email_Exception(
                          "Invalid e-mail address!", $email);

                  else
                      return 1;
               }
           } catch (Exception $e) {
                 echo $e->getMessage();
           } catch (Invalid_Email_Exception $e) {
                 echo $e->getMessage();
           }

}

/* This method would presumably add the user's e-mail address to
a database. */

        function subscribeUser() {
            echo $this->email." added to the database!";
        }

} #end Subscribe class

/* Assume that the e-mail address came from a subscription form. */

$_POST['email'] = "someuser@example.com";

    /* Attempt to validate and add address to database. */
    if (isset($_POST['email'])) {
        $subscribe = new Subscribe();
        if($subscribe->validateEmail($_POST['email']))
            $subscribe->subscribeUser($_POST['email']);
    }

You can see that it’s possible for two different exceptions to fire, one derived from the base class and one extended from the Invalid_Email_Exceptionclass.

Summary

The topics covered in this chapter touch upon many of the core error-handling practices used in today’s programming industry. While the implementation of such features unfortunately remains more preference than policy, the introduction of capabilities such as logging and error handling has contributed substantially to the ability of programmers to detect and respond to otherwise unforeseen problems in their code.

In the next chapter we take an in-depth look at PHP’s string-parsing capabilities, covering the language’s powerful regular expression features, and offering insight into many of the powerful string-manipulation functions.