扩展（extend） PHP 内置的异常处理类

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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  =  0 ,  Exception $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
 
 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 ,  Exception $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" ;
    }
}


 
 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 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" ; } } ?>

用户评论:

[#1] florenxe [2015-09-15 11:25:11]

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.

[#2] shaman_master at list dot ru [2014-12-14 00:57:07]

Use this example for not numeric codes:
<code>
<?php
class MyException extends Exception
{

    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>

[#3] hollodotme [2014-05-25 18:57:17]

Not mentioned in the class structure on top of this site are the following members:

<?php protected $string; protected $trace; protected $previous; ?>

... and these methods:

<?php final public function getPrevious(); ?>

[#4] michaelrfairhurst at gmail dot com [2012-10-15 04:55:58]

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') ); } ?>

[#5] Dor [2011-10-15 14:30:47]

It's important to note that subclasses of the Exception class will be caught by the default Exception handler

<?php 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, $previous); } } class TestException { const NONE = 0; const NORMAL = 1; const CUSTOM = 2; public function __construct($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).

[#6] iamhiddensomewhere at gmail dot com [2009-12-31 15:17:53]

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.

[#7] sapphirepaw.org [2009-11-24 07:37:44]

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.

[#8] paragdiwan at gmail dot com [2009-01-17 01:32:00]

I have written similar simple custom exception class. Helpful for newbie.
<?php 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; } ?>