Exceptions erweitern

Eine benutzerdefinierte Exceptionklasse kann durch Ableitung von der eingebauten Exceptionklasse erstellt werden. Die unten angegebenen Methoden und Eigenschaften zeigen, was innerhalb der Kindklasse von der eingebauten Exceptionklasse verfügbar ist.

Beispiel #1 Die eingebaute Exceptionklasse

<?php
class Exception
{
    protected 
$message 'Unknown exception';   // Exceptionmitteilung
    
private   $string;                          // __toString-Cache
    
protected $code 0;                        // Benutzerdefinierte Fehlernummer
    
protected $file;                            // Quelldateiname der Exception
    
protected $line;                            // Quelldateizeile der Exception
    
private   $trace;                           // Rückverfolgung
    
private   $previous;                        // Vorherige Exception, falls verschachtelte Exception

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

    final private function 
__clone();           // Verhindert klonen von Exceptions

    
final public function getMessage();         // Mitteilung der Exception
    
final public function getCode();            // Fehlercode der Exception
    
final public function getFile();            // Quelldateiname
    
final public function getLine();            // Quelldateizeile
    
final public function getTrace();           // Array zum Rückverfolgen
    
final public function getPrevious();        // Vorherige Exception
    
final public function getTraceAsString();   // Formatierter String der Rückverfolgung

    // Überschreibbar
    
public function __toString();               // Formatierter String für
                                                // Ausgabe
}
?>

Wenn eine Klasse die eingebaute Exceptionklasse erweitert und den Konstruktor neu definiert, ist es dringend empfohlen, dass der Konstruktor der Klasse parent::__construct() aufruft, um sicherzustellen, dass alle verfügbaren Daten korrekt zugewiesen wurden. Die __toString()-Methode kann überschrieben werden, um eine maßgeschneiderte Ausgabe anzubieten, wenn das Objekt durch eine Zeichenkette repräsentiert werden soll.

Hinweis:

Exceptions können nicht geklont werden. Der Versuch eine Exception zu klonen wird einen fatalen E_ERROR-Fehler zur Folge haben.

Beispiel #2 Die Exceptionklasse erweitern (PHP 5.3.0+)

<?php
/**
 * Eine maßgeschneiderte Exceptionklasse definieren
 */
class MyException extends Exception
{
    
// Die Exception neu definieren, damit die Mitteilung nicht optional ist
    
public function __construct($message$code 0Exception $previous null) {
        
// etwas Code

        // sicherstellen, dass alles korrekt zugewiesen wird
        
parent::__construct($message$code$previous);
    }

    
// maßgeschneiderte Stringdarstellung des Objektes
    
public function __toString() {
        return 
__CLASS__ ": [{$this->code}]: {$this->message}\n";
    }

    public function 
customFunction() {
        echo 
"Eine eigene Funktion dieses Exceptiontyps\n";
    }
}


/**
 * Erzeuge eine Klasse, um die Exception zu testen
 */
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:
                
// eigene Exception werfen
                
throw new MyException('1 ist ein ungültiger Parameter'5);
                break;

            case 
self::THROW_DEFAULT:
                
// Vorgabe werfen
                
throw new Exception('2 ist kein zugelassener Parameter'6);
                break;

            default:
                
// Keine Exception, das Objekt wird erzeugt
                
$this->var $avalue;
                break;
        }
    }
}


// Beispiel 1
try {
    
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
MyException $e) {      // Wird gefangen
    
echo "Meine Exception gefangen\n"$e;
    
$e->customFunction();
} catch (
Exception $e) {        // Übersprungen
    
echo "Standardexception gefangen\n"$e;
}

// Ausführung fortsetzen
var_dump($o); // Null
echo "\n\n";


// Beispiel 2
try {
    
$o = new TestException(TestException::THROW_DEFAULT);
} catch (
MyException $e) {      // Dieser Typ passt nicht
    
echo "Meine Exception gefangen\n"$e;
    
$e->customFunction();
} catch (
Exception $e) {        // Wird gefangen
    
echo "Standardexception gefangen\n"$e;
}

// Ausführung fortsetzen
var_dump($o); // Null
echo "\n\n";


// Beispiel 3
try {
    
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
Exception $e) {        // Wird gefangen
    
echo "Standardexception gefangen\n"$e;
}

// Ausführung fortsetzen
var_dump($o); // Null
echo "\n\n";


// Beispiel 4
try {
    
$o = new TestException();
} catch (
Exception $e) {        // Übersprungen, keine Exception ausgelöst
    
echo "Standardexception gefangen\n"$e;
}

// Ausführung fortsetzen
var_dump($o); // TestException
echo "\n\n";
?>

Hinweis:

PHP 5-Versionen vor PHP 5.3.0 unterstützen keine verschachtelten Exceptions. Für das Beispiel kann der folgende Code-Schnipsel als Ersatz für die Klasse MyException verwendet werden.

<?php
/**
 * Eine maßgeschneiderte Exceptionklasse definieren
 */
class MyException extends Exception
{
    
// Die Exception neu definieren, damit die Mitteilung nicht optional ist
    
public function __construct($message$code 0) {
        
// etwas Code

        // sicherstellen, dass alles korrekt zugewiesen wird
        
parent::__construct($message$code);
    }

    
// maßgeschneiderte Stringdarstellung des Objektes
    
public function __toString() {
        return 
__CLASS__ ": [{$this->code}]: {$this->message}\n";
    }

    public function 
customFunction() {
        echo 
"Eine eigene Funktion dieses Exceptiontyps\n";
    }
}
?>

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User Contributed Notes 7 notes

up
6
iamhiddensomewhere at gmail dot com
5 years ago
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 = 0, Exception $previous = null)
    {
       
parent::__construct($message, $code);
       
        if (!
is_null($previous))
        {
           
$this -> previous = $previous;
        }
    }
   
    public function
getPrevious()
    {
        return
$this -> previous;
    }
}

?>

Hope you find it useful.
up
2
sapphirepaw.org
5 years ago
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.
up
3
michaelrfairhurst at gmail dot com
2 years ago
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')
        );
}

?>
up
0
Dor
3 years ago
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 = 0, Exception $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).
up
-1
shaman_master at list dot ru
7 months ago
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 = 0, Exception $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>
up
-5
hollodotme
1 year ago
Not mentioned in the class structure on top of this site are the following members:

<?php
/**
* @var string
*/
protected $string;

/**
* @var array
*/
protected $trace;

/**
* @var Exception
*/
protected $previous;
?>

... and these methods:

<?php
/**
* @return Exception|null
*/
final public function getPrevious();
?>
up
-15
paragdiwan at gmail dot com
6 years ago
I have written similar simple custom exception class. Helpful for newbie.
<?php
   
/*
        This is written for overriding the exceptions.
        custom exception class
    */
   
error_reporting(E_ALL-E_NOTICE);
    class
myCustomException extends Exception
   
{
       
        public function
__construct($message, $code=0)
        {
           
parent::__construct($message,$code);
        }   

        public function
__toString()
        {
            return
"<b style='color:red'>".$this->message."</b>";
        }
       
       
    }

    class
testException
   
{
       
        public function
__construct($x)
        {
       
           
$this->x=$x;
           
        }
       
        function
see()
        {
           

            if(
$this->x==9 )
            {
                throw new
myCustomException("i didnt like it");
            }
        }
    }

   
$obj = new testException(9);
    try{
   
       
$obj->see();
    }
    catch(
myCustomException $e)
    {
        echo
$e;
    }
?>
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