扩展 PHP 内置的异常处理类

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。译者注:以下这段代码只为说明内置异常处理类的结构,它并不是一段有实际意义的可用代码。

Example #1 内置的异常处理类

<?php
class Exception
{
    protected 
$message 'Unknown exception';   // 异常信息
    
protected $code 0;                        // 用户自定义异常代码
    
protected $file;                            // 发生异常的文件名
    
protected $line;                            // 发生异常的代码行号

    
function __construct($message null$code 0);

    final function 
getMessage();                // 返回异常信息
    
final function getCode();                   // 返回异常代码
    
final function getFile();                   // 返回发生异常的文件名
    
final function getLine();                   // 返回发生异常的代码行号
    
final function getTrace();                  // backtrace() 数组
    
final function getTraceAsString();          // 已格成化成字符串的 getTrace() 信息

    /* 可重载的方法 */
    
function __toString();                       // 可输出的字符串
}
?>

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() 来检查所有的变量是否已被赋值。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。

Example #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) {
        
// 自定义的代码

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

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

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


/**
 * 创建一个用于测试异常处理机制的类
 */
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 isnt 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;
}

// 执行后续代码
var_dump($o);
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);
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);
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);
echo 
"\n\n";
?>
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User Contributed Notes 6 notes

up
2
iamhiddensomewhere at gmail dot com
4 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
1
michaelrfairhurst at gmail dot com
1 year 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
hollodotme
1 month 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
0
Dor
2 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
0
sapphirepaw.org
4 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
-5
paragdiwan at gmail dot com
5 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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