Exceptions

Содержание

- PHP 5 has an exception model similar to that of other programming languages. An exception can be thrown, try and caught within PHP. A Try block must include at least one catch block. Multiple catch blocks can be used to catch different classtypes; execution will continue after that last catch block defined in sequence. Exceptions can be thrown within catch blocks.

- When an exception is thrown, code following the statement will not be executed and PHP will attempt to find the first matching catch block. If an exception is not caught a PHP Fatal Error will be issued with an Uncaught Exception message, unless there has been a handler defined with set_exception_handler().

Пример 20-1. Throwing an Exception

<? try { $error = 'Always throw this error'; throw new Exception($error); //Code following an exception is not executed. echo 'Never executed'; } catch (Exception $e) { echo 'Caught exception: ', $e->getMessage(), "\n"; } //Continue execution echo 'Hello World';
?>

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.

Пример 20-2. The Built in Exception class

<? class Exception { protected $message = 'Unknown exception'; //exception message protected $code = 0; //user defined exception code protected $file; //source filename of exception protected $line; //source line of exception function __construct($message = null, $code = 0); final function getMessage(); //message of exception final function getCode(); //code of exception final function getFile(); //source filename final function getLine(); //source line final function getTrace(); //an array of the backtrace() final function getTraceAsString(); //formated string of trace /*Overrideable*/ function __toString(); //formated string for display }
?>

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

Пример 20-3. Extending the Exception class

<? /** * 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"; }} /** * 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 isnt 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); 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); 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); 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); echo "\n\n";
?>

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Ссылки. Разъяснения 22222

Глава 20. Exceptions

Extending Exceptions