php教程

扩展(extend) 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
    
private   $string;                          // __toString cache
    
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
    
private   $trace;                           // backtrace
    
private   $previous;                        // previous exception if nested exception

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

    final private function 
__clone();           // Inhibits cloning of exceptions.

    
final public  function getMessage();        // 返回异常信息
    
final public  function getCode();           // 返回异常代码
    
final public  function getFile();           // 返回发生异常的文件名
    
final public  function getLine();           // 返回发生异常的代码行号
    
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。

Note:

Exception 对象不能被复制。尝试对 Exception 对象复制 会导致一个 E_ERROR 级别的错误。

Example #2 扩展 PHP 内置的异常处理类 (PHP 5.3.0+)

<?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 0Exception $previous null) {
        
// 自定义的代码

        // 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 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;
}

// Continue execution
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";
?>

Note:

Versions of PHP 5, prior to PHP 5.3.0 do not support nesting of exceptions. The following code fragment can be used as a replacement MyException class if you wish to run this example.

<?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";
    }
}
?>

User Contributed Notes

Hayley Watson 25-Feb-2019 04:13
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.
florenxe 15-Sep-2015 11:25
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.
shaman_master at list dot ru 14-Dec-2014 12:57
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>
michaelrfairhurst at gmail dot com 15-Oct-2012 04:55
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')
        );
}

?>
Dor 15-Oct-2011 02:30
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).
iamhiddensomewhere at gmail dot com 31-Dec-2009 03:17
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.
sapphirepaw.org 24-Nov-2009 07:37
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.
paragdiwan at gmail dot com 17-Jan-2009 01:32
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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