PHP：附加到抛出的异常消息

Take the following function as an example of what I want to do:

public function save() {
    $this->connect('wb');
    try {
        if(!$this->lock())
            throw new Exception("Unable to acquire configuration locks");
        if (!$backup = $this->backup())
            throw new Exception("Failed to create configuration backup");
        try {
            if(!fwrite($this->_pointer, $this->dump("string")));
                throw new Exception("Error occured while writing to configuration");
            $this->unlock();
            $this->disconnect();
        } catch (Exception $e) {
            if(rename ($backup, $this->_file))
                $e .= PHP_EOL."Successfully restored configuration from backup";
            else
                $e .= PHP_EOL."Failed to restore configuration from backup";
            $this->unlock();
            $this->disconnect();
            throw $e;
        }
    } catch (Exception $e) {
        echo PHP_EOL, $e->getMessage();
    }
}

I have nested try() and catch() statements. An exception is thrown from the inner-most and is caught, I then perform some functions and throw another exception. Notice where I write $e .=, I understand this is the incorrect syntax. What I want to do is append the string to the exception's $e->getMessage().

How would I go about doing this?

Create you own exception class and create method for appending string to the message.

<?php
class SuperException extends Exception
{
    public function AppendToMessage($msg)
    {
        // $this->message is inherited from Exception class,
        // where it is protected field (member) of the class
        $this->message .= $msg;
    }
}
?>

Why not use a separate variable to keep the messages ?

public function save() {
    $this->connect('wb');
    $exceptionMessage = "";
    try {
        if(!$this->lock())
            throw new Exception("Unable to acquire configuration locks");
        if (!$backup = $this->backup())
            throw new Exception("Failed to create configuration backup");
        try {
            if(!fwrite($this->_pointer, $this->dump("string")));
                throw new Exception("Error occured while writing to configuration");
            $this->unlock();
            $this->disconnect();
        } catch (Exception $e) {
            if(rename ($backup, $this->_file))
                $exceptionMessage .= PHP_EOL."Successfully restored configuration from backup";
            else
                $exceptionMessage .= PHP_EOL."Failed to restore configuration from backup";
            $this->unlock();
            $this->disconnect();
            throw $e;
        }
    } catch (Exception $e) {
        echo PHP_EOL. $exceptionMessage . PHP_EOL . $e->getMessage();
    }
}

Most object-oriented language frameworks that support exception handling realize the need for this subject. You need to understand that Exceptions are not logs of what happened. Rather, they are there to pinpoint exactly where the error occurred.

So, not only that syntax is incorrect, the whole idea violates a dozen OOD principles. You should introduce a logger class, that collects information about the errors as you go, and use the exceptions to pinpoint the events that need to be recorded.

class ErrorLogger {

    private $log;

    public function __construct() {
        $this->log = array();
    }

    public function log(Exception $e) {
        array_push($this->log, $e->getMessage());
    }

}

and further in your code:

$logger = new ErrorLogger();
try {
    :
} catch (Exception $e) {
    $logger->log($e);
}