Extending Exceptions

A User defined Exception class can be defined by extending the built-in Exception class. The members and properties below, show what is accessible within the child class that derives from the built-in Exception class.

Example #1 The Built in Exception class

<?php
class Exception
{
    protected 
$message 'Unknown exception';   // exception message
    
private   $string;                          // __toString cache
    
protected $code 0;                        // user defined exception code
    
protected $file;                            // source filename of exception
    
protected $line;                            // source line of exception
    
private   $trace;                           // backtrace
    
private   $previous;                        // previous exception if nested exception

    
public function __construct($message null$code 0Exception $previous null);

    final private function 
__clone();           // Inhibits cloning of exceptions.

    
final public  function getMessage();        // message of exception
    
final public  function getCode();           // code of exception
    
final public  function getFile();           // source filename
    
final public  function getLine();           // source line
    
final public  function getTrace();          // an array of the backtrace()
    
final public  function getPrevious();       // previous exception
    
final public  function getTraceAsString();  // formatted string of trace

    // Overrideable
    
public function __toString();               // formatted string for display
}
?>

If a class extends the built-in Exception class and re-defines the constructor, it is highly recommended that it also call parent::__construct() to ensure all available data has been properly assigned. The __toString() method can be overridden to provide a custom output when the object is presented as a string.

Note:

Exceptions cannot be cloned. Attempting to clone an Exception will result in a fatal E_ERROR error.

Example #2 Extending the Exception class (PHP 5.3.0+)

<?php
/**
 * Define a custom exception class
 */
class MyException extends Exception
{
    
// Redefine the exception so message isn't optional
    
public function __construct($message$code 0Exception $previous null) {
        
// some code
    
        // make sure everything is assigned properly
        
parent::__construct($message$code$previous);
    }

    
// custom string representation of object
    
public function __toString() {
        return 
__CLASS__ ": [{$this->code}]: {$this->message}\n";
    }

    public function 
customFunction() {
        echo 
"A custom function for this type of exception\n";
    }
}


/**
 * Create a class to test the exception
 */
class TestException
{
    public 
$var;

    const 
THROW_NONE    0;
    const 
THROW_CUSTOM  1;
    const 
THROW_DEFAULT 2;

    function 
__construct($avalue self::THROW_NONE) {

        switch (
$avalue) {
            case 
self::THROW_CUSTOM:
                
// throw custom exception
                
throw new MyException('1 is an invalid parameter'5);
                break;

            case 
self::THROW_DEFAULT:
                
// throw default one.
                
throw new Exception('2 is not allowed as a parameter'6);
                break;

            default: 
                
// No exception, object will be created.
                
$this->var $avalue;
                break;
        }
    }
}


// Example 1
try {
    
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
MyException $e) {      // Will be caught
    
echo "Caught my exception\n"$e;
    
$e->customFunction();
} catch (
Exception $e) {        // Skipped
    
echo "Caught Default Exception\n"$e;
}

// Continue execution
var_dump($o); // Null
echo "\n\n";


// Example 2
try {
    
$o = new TestException(TestException::THROW_DEFAULT);
} catch (
MyException $e) {      // Doesn't match this type
    
echo "Caught my exception\n"$e;
    
$e->customFunction();
} catch (
Exception $e) {        // Will be caught
    
echo "Caught Default Exception\n"$e;
}

// Continue execution
var_dump($o); // Null
echo "\n\n";


// Example 3
try {
    
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
Exception $e) {        // Will be caught
    
echo "Default Exception caught\n"$e;
}

// Continue execution
var_dump($o); // Null
echo "\n\n";


// Example 4
try {
    
$o = new TestException();
} catch (
Exception $e) {        // Skipped, no exception
    
echo "Default Exception caught\n"$e;
}

// Continue execution
var_dump($o); // TestException
echo "\n\n";
?>

Note:

Versions of PHP 5, prior to PHP 5.3.0 do not support nesting of exceptions. The following code fragment can be used as a replacement MyException class if you wish to run this example.

<?php
/**
 * Define a custom exception class
 */
class MyException extends Exception
{
    
// Redefine the exception so message isn't optional
    
public function __construct($message$code 0) {
        
// some code
    
        // make sure everything is assigned properly
        
parent::__construct($message$code);
    }

    
// custom string representation of object
    
public function __toString() {
        return 
__CLASS__ ": [{$this->code}]: {$this->message}\n";
    }

    public function 
customFunction() {
        echo 
"A custom function for this type of exception\n";
    }
}
?>

Коментарии

Автор:
Support for exception linking was added in PHP 5.3.0. The getPrevious() method and the $previous argument to the constructor are not available on any built-in exceptions in older versions of PHP.
2009-11-24 09:37:44
http://php5.kiev.ua/manual/ru/language.exceptions.extending.html
As previously noted exception linking was recently added (and what a god-send it is, it certainly makes layer abstraction (and, by association, exception tracking) easier).

Since <5.3 was lacking this useful feature I took some initiative and creating a custom exception class that all of my exceptions inherit from:

<?php

class SystemException extends Exception
{
    private 
$previous;
   
    public function 
__construct($message$code 0Exception $previous null)
    {
       
parent::__construct($message$code);
       
        if (!
is_null($previous))
        {
           
$this -> previous $previous;
        }
    }
   
    public function 
getPrevious()
    {
        return 
$this -> previous;
    }
}

?>

Hope you find it useful.
2009-12-31 17:17:53
http://php5.kiev.ua/manual/ru/language.exceptions.extending.html
Автор:
It's important to note that subclasses of the Exception class will be caught by the default Exception handler

<?php
   
   
/**
     * NewException
     * Extends the Exception class so that the $message parameter is now mendatory.
     * 
     */
   
class NewException extends Exception {
       
//$message is now not optional, just for the extension.
       
public function __construct($message$code 0Exception $previous null) {
           
parent::__construct($message$code$previous);
        }
    }
   
   
/**
     * TestException
     * Tests and throws Exceptions.
     */
   
class TestException {
        const 
NONE 0;
        const 
NORMAL 1;
        const 
CUSTOM 2;
        public function 
__construct($type self::NONE) {
            switch (
$type) {
                case 
1
                    throw new 
Exception('Normal Exception');
                    break;
                case 
2:
                    throw new 
NewException('Custom Exception');
                    break;
                default:
                    return 
0//No exception is thrown.
           
}
        }
    }
   
    try {
       
$t = new TestException(TestException::CUSTOM);
    }
    catch (
Exception $e) {
       
print_r($e); //Exception Caught
   
}
   
?>

Note that if an Exception is caught once, it won't be caught again (even for a more specific handler).
2011-10-15 17:30:47
http://php5.kiev.ua/manual/ru/language.exceptions.extending.html
Custom exception classes can allow you to write tests that prove your exceptions
are meaningful. Usually testing exceptions, you either assert the message equals
something in which case you can't change the message format without refactoring,
or not make any assertions at all in which case you can get misleading messages
later down the line. Especially if your $e->getMessage is something complicated
like a var_dump'ed context array.

The solution is to abstract the error information from the Exception class into
properties that can be tested everywhere except the one test for your formatting.

<?php

class TestableException extends Exception {

        private 
$property;

        function 
__construct($property) {

               
$this->property $property;
               
parent::__construct($this->format($property));

        }

        function 
format($property) {
                return 
"I have formatted: " $property "!!";
        }

        function 
getProperty() {
                return 
$this->property;
        }

}

function 
testSomethingThrowsTestableException() {
        try {
                throw new 
TestableException('Property');
        } Catch (
TestableException $e) {
               
$this->assertEquals('Property'$e->getProperty());
        }
}

function 
testExceptionFormattingOnlyOnce() {
       
$e = new TestableException;
       
$this->assertEquals('I have formatted: properly for the only required test!!',
               
$e->format('properly for the only required test')
        );
}

?>
2012-10-15 07:55:58
http://php5.kiev.ua/manual/ru/language.exceptions.extending.html
Use this example for not numeric codes:
<code>
<?php
class MyException extends Exception
{
   
/**
     * Creates a new exception.
     *
     * @param string       $message   Error message
     * @param mixed       $code         The exception code
     * @param Exception $previous  Previous exception
     * @return void
     */
   
public function __construct($message ''$code 0Exception $previous null)
    {
       
// Pass the message and integer code to the parent
       
parent::__construct((string)$message, (int)$code$previous);

       
// @link http://bugs.php.net/39615 Save the unmodified code
       
$this->code $code;
    }
}
</
code>
2014-12-14 02:57:07
http://php5.kiev.ua/manual/ru/language.exceptions.extending.html
Автор:
Check the other SPL Exception classes and extend one of those if your intended exception is a subclass of one of those. This allows more finesse when catching.
2019-02-25 06:13:57
http://php5.kiev.ua/manual/ru/language.exceptions.extending.html

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