CascadiaPHP 2024

扩展(extend)异常处理类

用户可以用自定义的异常处理类来扩展 PHP 内置的异常处理类。以下的代码说明了在内置的异常处理类中,哪些属性和方法在子类中是可访问和可继承的。

示例 #1 内置的异常处理类

<?php
class Exception implements Throwable
{
protected
$message = 'Unknown exception'; // 异常信息
private $string; // __toString 的缓存
protected $code = 0; // 用户自定义异常错误码
protected $file; // 发生异常的源文件名
protected $line; // 发生异常的源代码行号
private $trace; // backtrace
private $previous; // 如果是嵌套异常,则是之前的 exception

public function __construct($message = '', $code = 0, Throwable $previous = null);

final private function
__clone(); // 禁止克隆异常。

final public function getMessage(); // 异常信息
final public function getCode(); // 异常错误码
final public function getFile(); // 发生异常的源文件名
final public function getLine(); // 发生异常的源代码行号
final public function getTrace(); // backtrace() 数组
final public function getPrevious(); // 之前的 exception
final public function getTraceAsString(); // 已格成化成字符串的 getTrace() 信息

// Overrideable
public function __toString(); // 可输出的格式化后的字符串
}
?>

如果使用自定义的类来扩展内置异常处理类,并且要重新定义构造函数的话,建议同时调用 parent::__construct() 来确保所有的变量已赋值。当对象要输出字符串的时候,可以重载 __toString() 并自定义输出的样式。

注意:

不能 复制 Exception 对象。尝试对 clone Exception 会导致 fatal E_ERROR 错误。

示例 #2 扩展 PHP 内置的异常处理类

<?php
/**
* 自定义一个异常处理类
*/
class MyException extends Exception
{
// 重定义构造器使 message 变为必须被指定的属性
public function __construct($message, $code = 0, Throwable $previous = null) {
// 这里写用户的代码

// 确保所有变量都被正确赋值
parent::__construct($message, $code, $previous);
}

// 自定义字符串输出的格式
public function __toString() {
return
__CLASS__ . ": [{$this->code}]: {$this->message}\n";
}

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


/**
* 创建一个类,测试该 exception 类
*/
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:
// 抛出自定义异常
throw new MyException('1 is an invalid parameter', 5);
break;

case
self::THROW_DEFAULT:
// 抛出默认的异常
throw new Exception('2 is not allowed as a parameter', 6);
break;

default:
// 没有异常的情况下,创建一个对象
$this->var = $avalue;
break;
}
}
}


// 例子 1
try {
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
MyException $e) { // 捕获异常
echo "Caught my exception\n", $e;
$e->customFunction();
} catch (
Exception $e) { // 被忽略
echo "Caught Default Exception\n", $e;
}

// 继续执行后续代码
var_dump($o); // Null
echo "\n\n";


// 例子 2
try {
$o = new TestException(TestException::THROW_DEFAULT);
} catch (
MyException $e) { // 不能匹配异常的种类,被忽略
echo "Caught my exception\n", $e;
$e->customFunction();
} catch (
Exception $e) { // 捕获异常
echo "Caught Default Exception\n", $e;
}

// 执行后续代码
var_dump($o); // Null
echo "\n\n";


// 例子 3
try {
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
Exception $e) { // 捕获异常
echo "Default Exception caught\n", $e;
}

// 执行后续代码
var_dump($o); // Null
echo "\n\n";


// 例子 4
try {
$o = new TestException();
} catch (
Exception $e) { // 没有异常,被忽略
echo "Default Exception caught\n", $e;
}

// 执行后续代码
var_dump($o); // TestException
echo "\n\n";
?>
add a note

User Contributed Notes 8 notes

up
3
Hayley Watson
5 years ago
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.
up
14
iamhiddensomewhere at gmail dot com
14 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
4
michaelrfairhurst at gmail dot com
11 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
3
sapphirepaw.org
14 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
0
Dor
12 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
-5
shaman_master at list dot ru
9 years 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
-15
florenxe
8 years ago
I just wanted to add that "extends" is same concept of "Inheritance" or "Prototyping in Javascript". So when you extend a class, you are simply inheriting the class's methods and properties. So you can create custom classes from existing classes like extending the array class.
up
-18
paragdiwan at gmail dot com
15 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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