Руководство по PHP
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# Глава 20. Exceptions

PHP 5 has an exception model similar to that of other programming languages. An exception can be `throw`n, and caught ("`catch`ed") within PHP. Code may be surrounded in a `try` block, to facilitate the catching of potential exceptions. Each `try` must have at least one corresponding `catch` block. Multiple `catch` blocks can be used to catch different classes of exeptions. Normal execution (when no exception is thrown within the `try` block, or when a `catch` matching the thrown exception's class is not present) will continue after that last catch block defined in sequence. Exceptions can be `throw`n (or re-thrown) within a `catch` block.

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 a handler has been defined with set_exception_handler().

Пример 20-1. Throwing an Exception

`<?php 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

`<?php
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

`<?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";
}
}
/**
* 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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