PHP exception handling related knowledge

 //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);
?>

The above code will get an error like this: Fatal error: Uncaught exception 'Exception' with message 'Value must be 1 or below' in C:webfoldertest.php:6 Stack trace: #0 C:webfoldertest.php(12): checkNum(28) #1 {main} thrown in C:webfoldertest.php on line 6 Try, throw and catch To avoid the errors in the above example, we need to create appropriate code to handle exceptions.

Processing procedures should include: Try - Functions that use exceptions should be inside a "try" block. If no exception is triggered, the code continues execution as usual. But if an exception is triggered, an exception will be thrown. Throw - This specifies how to trigger the exception. Each "throw" must correspond to at least one "catch" Catch - The "catch" code block will catch the exception and create an object containing the exception information

Let’s trigger an exception:

 //Create a function that can throw an exception
 function checkNum($number)
 {
 if($number>1)
 {
 throw new Exception("Value must be 1 or below");
 }
 return true;
 }

 //Trigger exception in "try" code block
 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';
 }

 //Catch exception
 catch(Exception $e)
 {
 echo 'Message: ' .$e->getMessage();
 }
?>

The above code will get an error similar to this: Message: Value must be 1 or below Example explanation: The code above throws an exception and catches it: Create checkNum() function. It detects whether the number is greater than 1. If so, throw an exception. Call the checkNum() function in the "try" block. Exception in checkNum() function is thrown The "catch" code block receives the exception and creates an object ($e) containing the exception information. 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 custom exception handlers 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 creating the exception class:

 class customException extends Exception
 {
 public function errorMessage()
 {
 //error message
 $errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
 .': '.$this->getMessage().' 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();
 }
 ?>

This new class is a copy of the old exception class, plus the errorMessage() function. Just because it is a copy of the old class, it inherits the properties and methods from the old class, and we can use the methods of the exception class, such as getLine(), getFile(), and getMessage(). Example explanation: The above code throws an exception and catches it through a custom exception class: The customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old class. Create errorMessage() function. If the e-mail address is not valid, this function returns an error message Set the $email variable to an illegal e-mail address string Execute the "try" code block and throw an exception because the e-mail address is invalid The "catch" code block catches the exception and displays the error message

Multiple exceptions

You can use multiple exceptions for a script to detect multiple situations.

You can use multiple if..else code blocks, or a switch code block, or nest multiple exceptions. These exceptions can use different exception classes and return different error messages:

 class customException extends Exception
 {
 public function errorMessage()
 {
 //error message
 $errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
 .': '.$this->getMessage().' 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();
 }
?>

Example explanation: The above code tests two conditions. If any condition is not true, an exception is thrown: The customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old class. Create errorMessage() function. If the e-mail address is not valid, this function returns an error message. Execute the "try" block of code, and in the first condition, no exception will be thrown. Since the e-mail contains the string "example", the second condition triggers an exception. The "catch" code block will catch the exception and display the appropriate error message

If customException is not caught and base exception is caught tightly, the exception is handled there. Rethrow the exception

Sometimes, when an exception is thrown, you may want to handle it differently than the standard way. The exception can be thrown again in a "catch" block.

The script should hide system errors from the user. System errors may be important to programmers, but users are not interested in them. To make it easier for users, you can throw the exception again with a user-friendly message:

 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();
 }
 ?> ;

Example explanation: The above code detects whether the string "example" is contained in the email address. If so, throw the exception again: The customException() class was created as an extension of the old exception class. This way it inherits all properties and methods of the old class. Create errorMessage() function. If the e-mail address is not valid, this function returns an error message. Set the $email variable to a valid email address, but containing the string "example". A "try" block contains another "try" block so that the exception can be thrown again. The exception is triggered because the e-mail contains the string "example". "catch" catches the exception and rethrows "customException". A "customException" is caught and an error message is displayed.

If the exception is not caught in its current "try" block, it will look for a catch block at a higher level.

Set the Top Level Exception Handler

The set_exception_handler() function can set a user-defined function that handles all uncaught exceptions.

 function myException($exception)
 {
 echo "Exception: " , $exception->getMessage();
 }

 set_exception_handler( 'myException');

 throw new Exception('Uncaught Exception occurred');
?>

The output of the above code should be similar to this: Exception: Uncaught Exception occurred In the above code, there is no "catch" block, instead the top-level exception handler is triggered. This function should be used to catch all uncaught exceptions. unusual rules Code that requires exception handling should be placed within a try block to catch potential exceptions. Every try or throw block must have at least one corresponding catch block. Use multiple catch blocks to catch different kinds of exceptions. Exceptions can be re-thrown in a catch block within a try block.

In short: if an exception is thrown, you must catch it.

Source: http://bbs.it-home.org/w3school/php/php_exception.html

Example:

 function throwTest($data)
 {
 try
 {
 if (!is_array($data) || emptyempty($data))
 {
 throw new Exception('data The type is not an array', 445);
 }
 echo('Done for testing!!');
 }
 catch (Exception $e)
 {
 /*echo 'Error message:',$e->getMessage( ), '';//Error message
 echo 'Error code:', $e->getCode(), '';//Error code
 echo 'Error file:', $e->getFile(), '';//Error file
 echo 'Error line number:', $e->getLine (), '';//Error line number
 echo 'Error information is displayed in an array:', print_r($e->getTrace()), '' ;//Error information is displayed as an array
 echo 'Error information is displayed as a string:', $e->getTraceAsString(), '';//Error information is displayed as a string* /
 echo $e->getMessage(), '';//Error message
 echo '', $e->getTraceAsString(), '' ;//Error information is displayed as a string
 exit;
 }
 }
 //$data=array("111","33333"); //Normal test
 $data="8129233"; //Abnormal test
 throwTest($data);
?>

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