PHP Exception

Exceptions are used to alter the normal flow of a script when a specified error occurs.

What is an exception

PHP 5 provides a new object-oriented error handling method.

Exception handling is used to change the normal flow of the script when a specified error (exception) situation occurs. This situation is called an exception.

When an exception is triggered, what typically happens is:

• The current code state is saved

• Code execution is switched to Predefined (custom) exception handler functions

• Depending on the situation, the handler may restart code execution from the saved code state, terminate script execution, or start another step in the code. Continue executing the script at location

We will show different error handling methods:

• Basic use of exceptions

• Create a custom exception handler

• Multiple exceptions

• Rethrow the exception

• Set the top-level exception handler

Note: Exceptions should only be used in error situations and should not be used to jump to a specified point Another location for the code.

Basic use of exceptions

When an exception is thrown, the subsequent 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 "Uncaught Exception" (uncaught exception) will be output. wrong information.

Let's try throwing an exception without catching it:

<?php
// 创建一个有异常处理的函数
function checkNum($number)
{
if($number>1)
{
throw new Exception("Value must be 1 or below");
}
return true;
}
// 触发异常
checkNum(2);
?>

Fatal error: Uncaught exception 'Exception' with message 'Value must be 1 or below' in /www/php/test/test.php:7 Stack trace: #0 /www/php/test/test.php(13): checkNum(2) #1 {main} thrown in /www/php/test/test.php on line ;

Try, throw and catch

To avoid the error that occurred in the above example, we need to create appropriate code to handle exceptions.

Appropriate exception handling code should include:

1. Try - Functions that use exceptions should be located within a "try" code block. If no exception is triggered, the code continues execution as usual. But if an exception is triggered, an exception will be thrown.

2. Throw - specifies how to trigger an exception. Each "throw" must correspond to at least one "catch".

3. Catch - The "catch" code block catches the exception and creates an object containing the exception information.

Let us trigger an exception:

<?php
// 创建一个有异常处理的函数
function checkNum($number)
{
if($number>1)
{
throw new Exception("变量值必须小于等于 1");
}
return true;
}
// 在 try 块 触发异常
try
{
checkNum(2);
// 如果抛出异常，以下文本不会输出
echo '如果输出该内容，说明 $number 变量';
}
// 捕获异常
catch(Exception $e)
{
echo 'Message: ' .$e->getMessage();
}
?>

Message: 变量值必须小于等于 1

Explanation of examples:

The above code throws an exception and catches it:

1. Create the checkNum() function. It detects whether the number is greater than 1. If so, throw an exception.

2. Call the checkNum() function in the "try" code block.

3. Exception in checkNum() function is thrown.

4. The "catch" code block receives the exception and creates an object ($e) containing the exception information.

5. Output the error message from this exception by calling $e->getMessage() from this exception object.

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.

Create a custom Exception class

Creating a custom exception handler is very simple. We simply created a specialized class whose functions are called when an exception occurs in PHP. This class must be an extension of the exception class.

This custom exception class inherits all properties of PHP's exception class, and you can add custom functions to it.

We start by creating the exception class:

<?php
class customException extends Exception
{
public function errorMessage()
{
// 错误信息
$errorMsg = '错误行号 '.$this->getLine().' in '.$this->getFile()
.': <b>'.$this->getMessage().'</b> 不是一个合法的 E-Mail 地址';
return $errorMsg;
}
}
$email = "someone@example...com";
try
{
// 检测邮箱
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
{
// 如果是个不合法的邮箱地址，抛出异常
throw new customException($email);
}
}
catch (customException $e)
{
//display custom message
echo $e->errorMessage();
}
?>

Explanation of examples:

The above code throws an exception and catches it through a custom exception class:

1. ## The #customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old exception class.

2. Create the errorMessage() function. If the e-mail address is not valid, this function returns an error message.

3. Set the $email variable to an illegal e-mail address string.

4. Execute the "try" code block and throw an exception because the e-mail address is illegal.

5. The "catch" code block catches the exception and displays an error message.

<?php
class customException extends Exception
{
public function errorMessage()
{
// 错误信息
$errorMsg = '错误行号 '.$this->getLine().' in '.$this->getFile()
.': <b>'.$this->getMessage().'</b> 不是一个合法的 E-Mail 地址';
return $errorMsg;
}
}
$email = "someone@example.com";
try
{
// 检测邮箱
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
{
// 如果是个不合法的邮箱地址，抛出异常
throw new customException($email);
}
// 检测 "example" 是否在邮箱地址中
if(strpos($email, "example") !== FALSE)
{
throw new Exception("$email 是 example 邮箱");
}
}
catch (customException $e)
{
echo $e->errorMessage();
}
catch(Exception $e)
{
echo $e->getMessage();
}
?>

<?php
class customException extends Exception
{
public function errorMessage()
{
// 错误信息
$errorMsg = $this->getMessage().' 不是一个合法的 E-Mail 地址。';
return $errorMsg;
}
}
$email = "someone@example.com";
try
{
try
{
// 检测 "example" 是否在邮箱地址中
if(strpos($email, "example") !== FALSE)
{
// 如果是个不合法的邮箱地址，抛出异常
throw new Exception($email);
}
}
catch(Exception $e)
{
// 重新抛出异常
throw new customException($email);
}
}
catch (customException $e)
{
// 显示自定义信息
echo $e->errorMessage();
}
?>

<?php
function myException($exception)
{
echo "<b>Exception:</b> " , $exception->getMessage();
}
set_exception_handler('myException');
throw new Exception('Uncaught Exception occurred');
?>

Exception: Uncaught Exception occurred