Author: aolinks
When an exception is thrown, the following code will not continue to execute, and PHP will try to find a matching "catch" code block.
If the exception is not caught and there is no need to use set_exception_handler() for corresponding processing, then a serious error (fatal error) will occur and an "Uncaught Exception" error message will be output.
Let’s try throwing an exception without catching it:
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9"><?php
//create function with an exception
function checkNum($number)
{
if($number>1)
{
throw new Exception("Value must be 1 or below");
}
return true;
}
//trigger exception
checkNum(2);
?></span>The above code will get an error like this:
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9">Fatal error: Uncaught exception 'Exception'
with message 'Value must be 1 or below' in C:\webfolder\test.php:6
Stack trace: #0 C:\webfolder\test.php(12):
checkNum(28) #1 {main} thrown in C:\webfolder\test.php on line 6</span>To avoid the errors in the above example, we need to create appropriate code to handle exceptions.
Processing procedures should include:
Let’s trigger an exception:
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9"><?php
//创建可抛出一个异常的函数
function checkNum($number)
{
if($number>1)
{
throw new Exception("Value must be 1 or below");
}
return true;
}
//在 "try" 代码块中触发异常
try
{
checkNum(2);
//If the exception is thrown, this text will not be shown
echo 'If you see this, the number is 1 or below';
}
//捕获异常
catch(Exception $e)
{
echo 'Message: ' .$e->getMessage();
}
?></span>The above code will get an error similar to this:
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9">Message: Value must be 1 or below </span>
The above code throws an exception and catches it:
However, in order to follow the principle of "each throw must correspond to a catch", you can set up a top-level exception handler to handle missed errors.
创建自定义的异常处理程序非常简单。我们简单地创建了一个专门的类，当 PHP 中发生异常时，可调用其函数。该类必须是 exception 类的一个扩展。
这个自定义的 exception 类继承了 PHP 的 exception 类的所有属性，您可向其添加自定义的函数。
我们开始创建 exception 类：
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9"><?php
class customException extends Exception
{
public function errorMessage()
{
//error message
$errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
.': <b>'.$this->getMessage().'</b> is not a valid E-Mail address';
return $errorMsg;
}
}
$email = "someone@example...com";
try
{
//check if
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
{
//throw exception if email is not valid
throw new customException($email);
}
}
catch (customException $e)
{
//display custom message
echo $e->errorMessage();
}
?></span>这个新的类是旧的 exception 类的副本，外加 errorMessage() 函数。正因为它是旧类的副本，因此它从旧类继承了属性和方法，我们可以使用 exception 类的方法，比如 getLine() 、 getFile() 以及 getMessage()。
上面的代码抛出了一个异常，并通过一个自定义的 exception 类来捕获它：
可以为一段脚本使用多个异常，来检测多种情况。
可以使用多个 if..else 代码块，或一个 switch 代码块，或者嵌套多个异常。这些异常能够使用不同的 exception 类，并返回不同的错误消息：
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9"><?php
class customException extends Exception
{
public function errorMessage()
{
//error message
$errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
.': <b>'.$this->getMessage().'</b> is not a valid E-Mail address';
return $errorMsg;
}
}
$email = "someone@example.com";
try
{
//check if
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
{
//throw exception if email is not valid
throw new customException($email);
}
//check for "example" in mail address
if(strpos($email, "example") !== FALSE)
{
throw new Exception("$email is an example e-mail");
}
}
catch (customException $e)
{
echo $e->errorMessage();
}
catch(Exception $e)
{
echo $e->getMessage();
}
?></span>上面的代码测试了两种条件，如何任何条件不成立，则抛出一个异常：
如果没有捕获 customException，紧紧捕获了 base exception，则在那里处理异常。
有时，当异常被抛出时，您也许希望以不同于标准的方式对它进行处理。可以在一个 "catch" 代码块中再次抛出异常。
脚本应该对用户隐藏系统错误。对程序员来说，系统错误也许很重要，但是用户对它们并不感兴趣。为了让用户更容易使用，您可以再次抛出带有对用户比较友好的消息的异常：
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9"><?php
class customException extends Exception
{
public function errorMessage()
{
//error message
$errorMsg = $this->getMessage().' is not a valid E-Mail address.';
return $errorMsg;
}
}
$email = "someone@example.com";
try
{
try
{
//check for "example" in mail address
if(strpos($email, "example") !== FALSE)
{
//throw exception if email is not valid
throw new Exception($email);
}
}
catch(Exception $e)
{
//re-throw exception
throw new customException($email);
}
}
catch (customException $e)
{
//display custom message
echo $e->errorMessage();
}
?></span>上面的代码检测在邮件地址中是否含有字符串 "example"。如果有，则再次抛出异常：
如果在其目前的 "try" 代码块中异常没有被捕获，则它将在更高层级上查找 catch 代码块。
set_exception_handler() 函数可设置处理所有未捕获异常的用户定义函数。
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9"><?php
function myException($exception)
{
echo "<b>Exception:</b> " , $exception->getMessage();
}
set_exception_handler('myException');
throw new Exception('Uncaught Exception occurred');
?></span>以上代码的输出应该类似这样：
<span class="Apple-style-span" style="line-height: normal; font-family: verdana, arial, helvetica, sans-serif; background-color: #f9f9f9">Exception: Uncaught Exception occurred</span>
在上面的代码中，不存在 "catch" 代码块，而是触发顶层的异常处理程序。应该使用此函数来捕获所有未被捕获的异常。
简而言之：如果抛出了异常，就必须捕获它
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