php教程

异常处理

Table of Contents

PHP 5 has an exception model similar to that of other programming languages. An exception can be thrown, and caught ("catched") within PHP. Code may be surrounded in a try block, to facilitate the catching of potential exceptions. Each try must have at least one corresponding catch or finally block.

The thrown object must be an instance of the Exception class or a subclass of Exception. Trying to throw an object that is not will result in a PHP Fatal Error.

catch

Multiple catch blocks can be used to catch different classes of exceptions. Normal execution (when no exception is thrown within the try block) will continue after that last catch block defined in sequence. Exceptions can be thrown (or re-thrown) within a catch block.

When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception ..." message, unless a handler has been defined with set_exception_handler().

finally

In PHP 5.5 and later, a finally block may also be specified after or instead of catch blocks. Code within the finally block will always be executed after the try and catch blocks, regardless of whether an exception has been thrown, and before normal execution resumes.

注释

Note:

Internal PHP functions mainly use Error reporting, only modern Object oriented extensions use exceptions. However, errors can be simply translated to exceptions with ErrorException.

Tip

The Standard PHP Library (SPL) provides a good number of built-in exceptions.

范例

Example #3 Throwing an Exception

<?php
function inverse($x) {
    if (!$x) {
        throw new Exception('Division by zero.');
    }
    return 1/$x;
}

try {
    echo inverse(5) . "\n";
    echo inverse(0) . "\n";
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "\n";
}

// Continue execution
echo "Hello World\n";
?>

以上例程会输出：

0.2
Caught exception: Division by zero.
Hello World

Example #4 Exception handling with a finally block

<?php
function inverse($x) {
    if (!$x) {
        throw new Exception('Division by zero.');
    }
    return 1/$x;
}

try {
    echo inverse(5) . "\n";
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "\n";
} finally {
    echo "First finally.\n";
}

try {
    echo inverse(0) . "\n";
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "\n";
} finally {
    echo "Second finally.\n";
}

// Continue execution
echo "Hello World\n";
?>

以上例程会输出：

0.2
First finally.
Caught exception: Division by zero.
Second finally.
Hello World

Example #5 Nested Exception

<?php

class MyException extends Exception { }

class Test {
    public function testing() {
        try {
            try {
                throw new MyException('foo!');
            } catch (MyException $e) {
                // rethrow it
                throw $e;
            }
        } catch (Exception $e) {
            var_dump($e->getMessage());
        }
    }
}

$foo = new Test;
$foo->testing();

?>

以上例程会输出：

string(4) "foo!"

User Contributed Notes

David Spector 06-Jul-2019 12:40
This page states, "Code may be surrounded in a try block, to facilitate the catching of potential exceptions." There are two ways in which code may be "surrounded". The obvious (intuitive) way is lexical enclosure: all the code to be protected by the try block is surrounded like this:

try
   {
   A();

   function A()
      {
      throw new Exception('error');
      echo "A()";
      } // A
   } // try
catch...

The other way to enclose is by execution (dynamic enclosure), like this:

try
   {
   A();
   } // try
catch...

function A()
   {
   throw new Exception('error');
   echo "A()";
   } // A

The sense in which code is "surrounded" for exception handling is dynamic (the second example above). This is because exception handling is dynamic and works by "unwinding" the execution stack.
wisetips at gmail dot com 01-Nov-2018 06:28
You should put your whole program into a try/catch block. Doing so is considered a best practice, because it will allow the user to continue to work even when there are errors in the page!
mlaopane at gmail dot com 24-Feb-2018 09:49
<?php

/**
 * You can catch exceptions thrown in a deep level function
 */

function employee()
{
    throw new \Exception("I am just an employee !");
}

function manager()
{
    employee();
}

function boss()
{
    try {
        manager();
    } catch (\Exception $e) {
        echo $e->getMessage();
    }
}

boss(); // output: "I am just an employee !"
jake at NOSPAM dot qzdesign dot co dot uk 08-Nov-2017 12:03
Don't forget if your source file is in a namespace you will need to
<?php
use Throwable; // PHP 7
use Exception;
?>
or type the fully qualified class name (prefixed with `\`) as in
<?php
try {
  // ...
} catch(\Throwable $e) {
  // PHP 7
} catch(\Exception $e) {
  // PHP 5
}
?>
otherwise you will only ever catch exceptions of the possibly non-existent classes `\YourNamespace\Throwable` and `\YourNamespace\Exception`!
daviddlowe dot flimm at gmail dot com 22-Sep-2017 01:13
Starting in PHP 7, the classes Exception and Error both implement the Throwable interface. This means, if you want to catch both Error instances and Exception instances, you should catch Throwable objects, like this:

<?php

try {
    throw new Error( "foobar" );
    // or:
    // throw new Exception( "foobar" );
}
catch (Throwable $e) {
    var_export( $e );
}

?>
jenshausdorf at gmail dot com 08-Jul-2017 09:10
Please don't do something like this:

<?php
try {
    // experimental stuff to check whether something works
} catch(\Throwable $e) {
    return false;
} finally {
    return true;
}
?>

Well, it is allowed syntax, it is bad practice, because once it hits the exception block, finally won't be called(because it exits the scope). Finally was invented to prevent duplicated code after one operation, regardless whether it was successful(for example closing the connection to a server). This way, you don't have any duplicated code. So you don't need to use this structure.
christof+php[AT]insypro.com 15-Jun-2017 10:12
In case your E_WARNING type of errors aren't catchable with try/catch you can change them to another type of error like this:

<?php
    set_error_handler(function($errno, $errstr, $errfile, $errline){
            if($errno === E_WARNING){
                // make it more serious than a warning so it can be caught
                trigger_error($errstr, E_ERROR);
                return true;
            } else {
                // fallback to default php error handler
                return false;
            }
    });

    try {
            // code that might result in a E_WARNING
    } catch(Exception $e){
            // code to handle the E_WARNING (it's actually changed to E_ERROR at this point)
    } finally {
            restore_error_handler();
    }
?>
ohcc at 163 dot com 11-Aug-2016 09:25
If a TRY has a FINALLY, a RETURN either in the TRY or a CATCH won't terminate the script. Code in the same block after the RETURN will not be executed, and the RETURN itself will be "copied" to the bottom of the FINALLY block to be executed.

a RETURN in the FINALLY block will override value(s) returned from the TRY or a CATCH block.

An EXIT or a DIE always terminate the script after themselves.

code 1

<?php
    function foo(){
        $bar = 1;
        try{
            throw new Exception('I am Wu Xiancheng.');
        }catch(Exception $e){
            return $bar;
            $bar--; // this line will be ignored
        }finally{
            $bar++;
        }
    }
    echo foo(); // 2
?>

code 2

<?php
    function foo(){
        $bar = 1;
        try{
            throw new Exception('I am Wu Xiancheng.');
        }catch(Exception $e){
            return $bar;
            $bar--; // this line will be ignored
        }finally{
            $bar++;
            return $bar;
        }
    }
    echo foo(); //2
?>

code 3

<?php
    function foo(){
        $bar = 1;
        try{
            throw new Exception('I am Wu Xiancheng.');
        }catch(Exception $e){
            return $bar;
            $bar--; // this line will be ignored
        }finally{
            return 100;
        }
    }
    echo foo(); //100
?>
Mohammad Hossein Darvishanpour 11-Apr-2016 07:05
<?php
function Test_Extention($var1)
{
    if($var1 == false)
    {
        throw new Exception('Invalid !');
    }
}//end function

try
{
    Test_Extention(false);
    printf("%s","Valid");
}

catch(Exception $e)
{
    printf("%s","Message : " . $e->getMessage());
}
?>
ohcc at 163 dot com 07-Nov-2015 05:40
Type declarations will trigger Uncaught TypeError when a different type is passed. And it cannot be caught with the Exception class.
<?php
    function xc(array $a){       
    }   
    try{
        xc(4);
    }catch (Exception $e){ // failed to catch it
        echo $e->getMessage();
    }
?>

You should use TypeError instead for PHP 7+,

<?php
    function xc(array $a){   
    }   
    try{
        xc(4);
    }catch (TypeError $e){
        echo $e->getMessage();
    }
?>

In php version prior to 7.0, you should translate Catchable fatal errors to an exception and then catch it.

<?php
    function exceptionErrorHandler($errNumber, $errStr, $errFile, $errLine ) {
        throw new ErrorException($errStr, 0, $errNumber, $errFile, $errLine);
    }
    set_error_handler('exceptionErrorHandler');
    function s(array $a){       
    }
    try{
        s(4);
    }catch (Exception $e){
        echo $e->getMessage();
    }
?>
hweidmann at online dot de 26-Sep-2015 08:20
catch doesn't check for the existence of the Exception class, so avoid typo.

<?php
   class MyException extends Exception
   {
      ...
   }

   try
   {
      throw new MyException(...);
   }
   catch (MuException $e) // <--- typo
   {
      ...
   }
?>

You WON'T get
   Fatal error: Class MuException could not be loaded ...

You WILL get
   Fatal error: Uncaught exception 'MyException' ...
Simo 04-Apr-2015 02:47
#3 is not a good example. inverse("0a") would not be caught since (bool) "0a" returns true, yet 1/"0a" casts the string to integer zero and attempts to perform the calculation.
Tom Polomsk 04-Dec-2014 01:45
Contrary to the documentation it is possible in PHP 5.5 and higher use only try-finally blocks without any catch block.
Hayley Watson 23-Jun-2014 06:58
Remember that Exceptions are also objects and can be handled as such; they can be constructed in and returned as values from functions, passed as arguments to other functions, and examined before being thrown. You don't have to throw it as soon as you have constructed it (the stack trace will of course reflect the moment the Exception was constructed, not the moment it was thrown).

You might, for example, want to collect additional information to include in YourException but you don't want to clutter up the YourException class or the code containing the "throw" statement by collecting the information there. Or you might want to do something (such as logging) with each Exception that is thrown from a certain region (catch it, pass it to the logging function, then rethrow it).
telefoontoestel at nospam dot org 18-Jun-2014 12:34
When using finally keep in mind that when a exit/die statement is used in the catch block it will NOT go through the finally block.

<?php
try {
    echo "try block<br />";
    throw new Exception("test");
} catch (Exception $ex) {
    echo "catch block<br />";
} finally {
    echo "finally block<br />";
}

// try block
// catch block
// finally block
?>

<?php
try {
    echo "try block<br />";
    throw new Exception("test");
} catch (Exception $ex) {
    echo "catch block<br />";
    exit(1);
} finally {
    echo "finally block<br />";
}

// try block
// catch block
?>
php at marcuspope dot com 24-Jan-2014 05:42
Using a return statement inside a finally block will override any other return statement or thrown exception from the try block and all defined catch blocks.   Code execution in the parent stack will continue as if the exception was never thrown. 

Frankly this is a good design decision because it means I can optionally dismiss all thrown exceptions from 1 or more catch blocks in one place, without having to nest my whole try block inside an additional (and otherwise needless) try/catch block.

This is the same behavior as Java, whereas C# throws a compile time error when a return statement exists inside a finally block.  So I figured it was worth pointing out to PHP devs who may not have any exposure to finally blocks or how other languages do it.

<?php

function asdf()
{
    try {
        throw new Exception('error');
    }
    catch(Exception $e) {
        echo "An error occurred";
        throw $e;
    }
    finally {
                //This overrides the exception as if it were never thrown
        return "\nException erased";
    }
}

try {
    echo asdf();
}
catch(Exception $e) {
    echo "\nResult: " . $e->getMessage();
}
?>

The output from above will look like this:

    An error occurred
    Exception erased

Without the return statement in the finally block it would look like this:

    An error occurred
    Result: error
cyrus+php at boadway dot ca 02-Oct-2013 02:50
There's some inconsistent behaviour associated with PHP 5.5.3's finally and return statements. If a method returns a variable in a try block (e.g. return $foo;), and finally modifies that variable, the /modified/ value is returned. However, if the try block has a return that has to be evaluated in-line (e.g. return $foo+0;), finally's changes to $foo will /not/ affect the return value.

[code]
function returnVariable(){
    $foo = 1;
    try{
        return $foo;
    } finally {
        $foo++;
    }
}

function returnVariablePlusZero(){
    $foo = 1;
    try{
        return $foo + 0;
    } finally {
        $foo++;
    }
}

$test1 = returnVariable(); // returns 2, not the correct value of 1.
$test2 = returnVariablePlusZero(); // returns correct value of 1, but inconsistent with $test1.
[/code]

It looks like it's trying to be efficient by not allocating additional memory for the return value when it thinks it doesn't have to, but the spec is that finally is run after try is completed execution, and that includes the evaluation of the return expression.

One could argue (weakly) that the first method should be the correct result, but at least the two methods should be consistent.
jim at anderos dot com 27-Sep-2013 05:22
If you are using a namespace, you must indicate the global namespace when using Exceptions.
<?php
namespace alpha;
function foo(){
    throw new \Exception("Something is wrong!");
    // throw new Exception(""); will fail
}

try {
    foo();
} catch( \Exception $e ) {
    // catch( Exception $e ) will give no warning, but will not catch Exception
    echo "ERROR: $e";
}

?>
sander at rotorsolutions dot nl 26-Jun-2013 02:08
Just an example why finally blocks are usefull (5.5)

<?php

//without catch
function example() {
  try {
    //do something that throws an exeption
  }
  finally {
    //this code will be executed even when the exception is executed
  }
}

function example2() {
  try {
     //open sql connection check user as example
     if(condition) {
        return false;
     }
  }
  finally {
    //close the sql connection, this will be executed even if the return is called.
  }
}
sander at rotorsolutions dot nl 26-Jun-2013 02:05
Just an example why finally blocks are usefull (5.5)

<?php

//without catch
function example() {
  try {
    //do something that throws an exeption
  }
  finally {
    //this code will be executed even when the exception is executed
  }
}

function example2() {
  try {
     //open sql connection check user as example
     if(condition) {
        return false;
     }
  }
  finally {
    //close the sql connection, this will be executed even if the return is called.
  }
}

?>
Edu 24-Jun-2013 06:13
The "finally" block can change the exception that has been throw by the catch block.

<?php
try{
        try {
                throw new \Exception("Hello");
        } catch(\Exception $e) {
                echo $e->getMessage()." catch in\n";
                throw $e;
        } finally {
                echo $e->getMessage()." finally \n";
                throw new \Exception("Bye");
        }
} catch (\Exception $e) {
        echo $e->getMessage()." catch out\n";
}
?>

The output is:

Hello catch in
Hello finally
Bye catch out
Sawsan 28-Nov-2011 09:36
the following is an example of a re-thrown exception and the using of getPrevious function:

<?php

$name = "Name";

//check if the name contains only letters, and does not contain the word name

try
   {
   try
     {
      if (preg_match('/[^a-z]/i', $name))
       {
           throw new Exception("$name contains character other than a-z A-Z");
       }  
       if(strpos(strtolower($name), 'name') !== FALSE)
       {
          throw new Exception("$name contains the word name");
       }
       echo "The Name is valid";
     }
   catch(Exception $e)
     {
     throw new Exception("insert name again",0,$e);
     }
   }
 
catch (Exception $e)
   {
   if ($e->getPrevious())
   {
    echo "The Previous Exception is: ".$e->getPrevious()->getMessage()."<br/>";
   }
   echo "The Exception is: ".$e->getMessage()."<br/>";
   }

 ?>
alex dowgailenko [at] g mail . com 27-Jul-2011 12:20
If you use the set_error_handler() to throw exceptions of errors, you may encounter issues with __autoload() functionality saying that your class doesn't exist and that's it.

If you do this:

<?php

class MyException extends Exception
{
}

class Tester
{
    public function foobar()
    {
        try
        {
            $this->helloWorld();
        } catch (MyException $e) {
            throw new Exception('Problem in foobar',0,$e);
        }
    }
   
    protected function helloWorld()
    {
        throw new MyException('Problem in helloWorld()');
    }
}

$tester = new Tester;
try
{
    $tester->foobar();
} catch (Exception $e) {
    echo $e->getTraceAsString();
}
?>

The trace will only show $tester->foobar() and not the call made to $tester->helloWorld().

In other words, if you pass a previous exception to a new one, the previous exception's stack trace is taken into account in the new exception.
Johan 05-May-2011 01:18
Custom error handling on entire pages can avoid half rendered pages for the users:

<?php
ob_start();
try {
    /*contains all page logic
    and throws error if needed*/
    ...
} catch (Exception $e) {
  ob_end_clean();
  displayErrorPage($e->getMessage());
}
?>
zmunoz at gmail dot com 18-May-2010 01:05
When catching an exception inside a namespace it is important that you escape to the global space:

<?php
 namespace SomeNamespace;

 class SomeClass {

  function SomeFunction() {
   try {
    throw new Exception('Some Error Message');
   } catch (\Exception $e) {
    var_dump($e->getMessage());
   }
  }

 }
?>
ask at nilpo dot com 27-May-2009 12:19
If you intend on creating a lot of custom exceptions, you may find this code useful.  I've created an interface and an abstract exception class that ensures that all parts of the built-in Exception class are preserved in child classes.  It also properly pushes all information back to the parent constructor ensuring that nothing is lost.  This allows you to quickly create new exceptions on the fly.  It also overrides the default __toString method with a more thorough one.

<?php
interface IException
{
    /* Protected methods inherited from Exception class */
    public function getMessage();                 // Exception message
    public function getCode();                    // User-defined Exception code
    public function getFile();                    // Source filename
    public function getLine();                    // Source line
    public function getTrace();                   // An array of the backtrace()
    public function getTraceAsString();           // Formated string of trace
   
    /* Overrideable methods inherited from Exception class */
    public function __toString();                 // formated string for display
    public function __construct($message = null, $code = 0);
}

abstract class CustomException extends Exception implements IException
{
    protected $message = 'Unknown exception';     // Exception message
    private   $string;                            // Unknown
    protected $code    = 0;                       // User-defined exception code
    protected $file;                              // Source filename of exception
    protected $line;                              // Source line of exception
    private   $trace;                             // Unknown

    public function __construct($message = null, $code = 0)
    {
        if (!$message) {
            throw new $this('Unknown '. get_class($this));
        }
        parent::__construct($message, $code);
    }
   
    public function __toString()
    {
        return get_class($this) . " '{$this->message}' in {$this->file}({$this->line})\n"
                                . "{$this->getTraceAsString()}";
    }
}
?>

Now you can create new exceptions in one line:

<?php
class TestException extends CustomException {}
?>

Here's a test that shows that all information is properly preserved throughout the backtrace.

<?php
function exceptionTest()
{
    try {
        throw new TestException();
    }
    catch (TestException $e) {
        echo "Caught TestException ('{$e->getMessage()}')\n{$e}\n";
    }
    catch (Exception $e) {
        echo "Caught Exception ('{$e->getMessage()}')\n{$e}\n";
    }
}

echo '<pre>' . exceptionTest() . '</pre>';
?>

Here's a sample output:

Caught TestException ('Unknown TestException')
TestException 'Unknown TestException' in C:\xampp\htdocs\CustomException\CustomException.php(31)
#0 C:\xampp\htdocs\CustomException\ExceptionTest.php(19): CustomException->__construct()
#1 C:\xampp\htdocs\CustomException\ExceptionTest.php(43): exceptionTest()
#2 {main}
Shot (Piotr Szotkowski) 21-Oct-2008 12:13
'Normal execution (when no exception is thrown within the try block, *or when a catch matching the thrown exception's class is not present*) will continue after that last catch block defined in sequence.'

'If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception ..." message, unless a handler has been defined with set_exception_handler().'

These two sentences seem a bit contradicting about what happens 'when a catch matching the thrown exception's class is not present' (and the second sentence is actually correct).
michael dot ochs at gmx dot net 21-Mar-2008 03:44
Actually it isn't possible to do:
<?php
someFunction() OR throw new Exception();
?>

This leads to a T_THROW Syntax Error. If you want to use this kind of exceptions, you can do the following:

<?php
function throwException($message = null,$code = null) {
    throw new Exception($message,$code);
}

someFunction() OR throwException();
?>
jon at hackcraft dot net 24-Jan-2007 09:52
Further to dexen at google dot me dot up with "use destructors to perform a cleanup in case of exception". The fact that PHP5 has destructors, exception handling, and predictable garbage collection (if there's a single reference in scope and the scope is left then the destructor is called immediately) allows for the use of the RAII idiom.

http://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization and my own http://www.hackcraft.net/RAII/ describe this.
jazfresh at hotmail.com 07-Aug-2006 10:18
Sometimes you want a single catch() to catch multiple types of Exception. In a language like Python, you can specify multiple types in a catch(), but in PHP you can only specify one. This can be annoying when you want handle many different Exceptions with the same catch() block.

However, you can replicate the functionality somewhat, because catch(<classname> $var) will match the given <classname> *or any of it's sub-classes*.

For example:

<?php
class DisplayException extends Exception {};
class FileException extends Exception {};
class AccessControl extends FileException {}; // Sub-class of FileException
class IOError extends FileException {}; // Sub-class of FileException

try {
  if(!is_readable($somefile))
     throw new IOError("File is not readable!");
  if(!user_has_access_to_file($someuser, $somefile))
     throw new AccessControl("Permission denied!");
  if(!display_file($somefile))
     throw new DisplayException("Couldn't display file!");

} catch (FileException $e) {
  // This block will catch FileException, AccessControl or IOError exceptions, but not Exceptions or DisplayExceptions.
  echo "File error: ".$e->getMessage();
  exit(1);
}
?>

Corollary: If you want to catch *any* exception, no matter what the type, just use "catch(Exception $var)", because all exceptions are sub-classes of the built-in Exception.
fjoggen at gmail dot com 26-Apr-2006 01:58
This code will turn php errors into exceptions:

<?php
function exceptions_error_handler($severity, $message, $filename, $lineno) {
    throw new ErrorException($message, 0, $severity, $filename, $lineno);
}

set_error_handler('exceptions_error_handler');
?>

However since <?php set_error_handler()?> doesn't work with fatal errors, you will not be able to throw them as Exceptions.

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