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Object-Oriented Programming with PHP

Customizing PHP exceptions


From:

Object-Oriented Programming with PHP

with Jon Peck

Video: Customizing PHP exceptions

In the previous segment, we threw an exception, because of an unknown address ID, but didn't catch it, which resulted in a fatal error. Let's make the demo more resilient, and deal with this unfortunate circumstance by wrapping the load attempt in a try block. I'm going to switch the demo. try. A catch block must follow the try block. The catch block doesn't have to be immediately afterwards, and other code can execute in between, but it's generally best practice to have the catch as close to the try as possible.
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  1. 4m 10s
    1. Welcome
      39s
    2. Exercise files
      2m 16s
    3. What you should know
      1m 15s
  2. 7m 47s
    1. What is an object?
      2m 6s
    2. What is a class?
      2m 7s
    3. Why should you use object-oriented programming?
      2m 14s
    4. The history of object-oriented PHP
      1m 20s
  3. 16m 40s
    1. Defining a class
      2m 58s
    2. Defining class properties
      3m 26s
    3. Creating a method and exploring object context with $this
      2m 50s
    4. Instantiating an object and accessing its contents
      3m 19s
    5. Specifying the visibility scope
      4m 7s
  4. 15m 51s
    1. What is a magic method, and do I need one?
      2m 23s
    2. Overloading property access
      6m 37s
    3. Customizing object construction
      4m 34s
    4. Standardizing object rendering as a string
      2m 17s
  5. 20m 54s
    1. Using the static keyword
      3m 36s
    2. Leveraging scope resolution operators
      1m 10s
    3. Setting constant values
      2m 47s
    4. Implementing static methods
      5m 43s
    5. Creating a database class
      7m 38s
  6. 26m 19s
    1. Extending your class
      6m 8s
    2. Abstracting classes
      5m 57s
    3. Sharing interfaces using polymorphism
      4m 39s
    4. Overriding methods, properties, and constants
      3m 25s
    5. Cloning and comparing objects
      2m 51s
    6. Referencing objects
      3m 19s
  7. 14m 52s
    1. Leveraging standard class objects
      2m 42s
    2. Retrieving objects from the database
      5m 41s
    3. Error handling with exceptions
      2m 6s
    4. Customizing PHP exceptions
      4m 23s
  8. 8m 2s
    1. Identifying the singleton pattern
      1m 42s
    2. Using the factory method pattern
      1m 51s
    3. Implementing a strategy pattern
      4m 29s
  9. 2m 57s
    1. Looking forward to namespaces
      47s
    2. Next steps
      1m 6s
    3. Goodbye
      1m 4s

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Object-Oriented Programming with PHP
1h 57m Intermediate Sep 26, 2012 Updated Apr 10, 2013

Viewers: in countries Watching now:

Whether you're enhancing or optimizing existing code or just starting from scratch, there's never a better time to start integrating object-oriented design techniques. This course shows how to integrate the principles of object-oriented programming into the build of a PHP-driven web page or application. After an overview of what objects and classes are and why they should be used, author Jon Peck dives into creating and instantiating objects, then defining the class relationships and interactions that will form the basis of your coding arsenal. The course also shows how to leverage PHP objects and implement design patterns, and looks at steps you can take to continue adding to your programming tool belt.

Topics include:
  • Historical overview of object-oriented PHP
  • Defining classes
  • Creating a method/object context with $this
  • Accessing classes without instantiation
  • Creating a database class
  • Extending and abstracting classes
  • Cloning and comparing objects
  • Error handling with exceptions
  • Implementing design patterns, such as the factory and strategy patterns
Subjects:
Developer Programming Languages
Software:
PHP
Author:
Jon Peck

Customizing PHP exceptions

In the previous segment, we threw an exception, because of an unknown address ID, but didn't catch it, which resulted in a fatal error. Let's make the demo more resilient, and deal with this unfortunate circumstance by wrapping the load attempt in a try block. I'm going to switch the demo. try. A catch block must follow the try block. The catch block doesn't have to be immediately afterwards, and other code can execute in between, but it's generally best practice to have the catch as close to the try as possible.

To catch an exception, use the catch keyword, followed by parentheses containing the class of the exception you wish to catch, which is the same as what was thrown, and a variable to put the thrown exception in, if any. Let's catch that exception. catch parentheses Exception $e. Once caught, you can optionally take further action. In this case, rendering the message that was included in the thrown exception is sufficient. Often, exception messages are intended for debugging.

So, consider what is actually being displayed to the user before just displaying an exception message. echo $e getMessage. Save the demo, then reload the page. The exception message is displayed, which is much more graceful than a fatal exit. To further customize the exception, extend the Exception class with your own custom Exception subclass. Go back to your editor, then create a new file called class.Exceptionaddress.inc.

Create a new class named ExceptionAddress that extends the PHP exception class. class ExceptionAddress extends Exception. We'll add PHP doc. There are number of built-in methods that you can override. One of them is the magic to string method. Magic_toString. return string. public function_toString.

Use the magic constant class to display the name of the current class. Return the class, the exception code, and the exception message. return_CLASS double quotes {this code} {this message}. Save the exception address class. Now that the exception is extended as an exception address, update the load method to throw the new exception address class.

Save, then edit the demo script to catch the new exception address, and use the magic to string method. Save, then run the demo. You will see the new exception address message, but the code is set to 0, which isn't very helpful. Exception codes are typically integers. Let's use a consonant to define a custom exception code. Return to your editor, and then go to the top of your address class. Define a new constant. const ADDRESS_ERROR_NOT_FOUND = 1000. Then, edit the throw and the load method to include the code.

Remember that load is static, so use the self keyword, not "this." The second argument of the exception is the code. self::ADDRESS_ERROR_NOT_FOUND. Save, then reload the demo page. ExceptionAddress now has an error code. If I wanted to define multiple behaviors, depending on the circumstance, I'd create additional error codes, then use an if or a switch statement to decide what to do, based on the error code.

Throughout this chapter, I've gone over a number of PHP's built-in objects. I started with generic standard classes, then retrieved objects directly from the database. We gracefully dealt with potentially fatal problems, then customized errors to meet our needs. In the next chapter, I'm going to discuss some common coding design patterns that I've used throughout this course.

Find answers to the most frequently asked questions about Object-Oriented Programming with PHP.


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Q: I'm not seeing warnings or errors in my environment like the video; why not?
A: Your PHP configuration is probably configured not to show them to you. This is often true on commercial web hosts and is often the default. Fortunately, there are multiple ways of resolving this.

The easiest way would be to explicitly enable error reporting at the top of the PHP script you wish to debug.

error_reporting(E_ALL | E_STRICT);
ini_set('display_errors', 1);

Alternatively, if you have access to your php.ini file and you want to always have error reporting on, change error_reporting = to a development friendly value of

error_reporting = E_ALL | E_STRICT

then change display_errors = to

display_errors = On

Finally, if access to the php.ini file is not available, you can add the following directives to your .htaccess or VirtualHost configuration for Apache:

php_value error_reporting 32767
php_value display_errors 1

If you would like a development optimized development environment like the one utilized in this course, see Up and Running with Linux for PHP Developers, here in the lynda.com online training library.

Q: This course was updated on 4/10/2013. What changed?

A: The author rerecorded some of the tutorials to add more background information and better graphics.

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