PHP Exception Handling: Try, Catch, Finally & Custom Exception Classes

In production web development, errors are inevitable: a database server might go offline, a requested file might be deleted, or a user might enter invalid input. In legacy PHP, unhandled errors displayed ugly fatal crashes to visitors. Modern PHP utilizes structured Exception Handling using try, catch, finally, and custom Exception classes to gracefully capture runtime failures without halting the server.

Syntax: The try...catch...finally Construct

<?php
    function calculateSemesterDivision(int $totalMarks, int $totalSubjects): float {
        if ($totalSubjects <= 0) {
            // Throw an exception when an illegal condition occurs
            throw new InvalidArgumentException("Number of subjects must be greater than zero.");
        }
        return $totalMarks / $totalSubjects;
    }

    try {
        // Code that might fail
        $average = calculateSemesterDivision(450, 0); // Will trigger exception!
        echo "Calculated Average: " . $average;
    } catch (InvalidArgumentException $e) {
        // Gracefully catch and handle the specific error
        echo "<div style='color:red;'>Calculation Error: " . $e->getMessage() . "</div>";
    } finally {
        // ALWAYS executes regardless of whether an error occurred
        echo "<p>Calculation routine complete.</p>";
    }
?>

Catching Multiple Exception Types

In PHP 7.1+, you can catch multiple related exception classes in a single catch block using the pipe operator (|):

<?php
    try {
        // Complex database and file logic...
    } catch (PDOException | IOException $e) {
        // Handles both database and filesystem failures together
        error_log($e->getMessage());
        echo "A system infrastructure error occurred. Support has been notified.";
    }
?>

Creating Custom Application Exception Classes

<?php
    // Custom domain exception
    class StudentNotFoundException extends Exception {}

    class StudentService {
        public function findStudent(int $id): string {
            if ($id !== 101) {
                throw new StudentNotFoundException("Student with ID #$id was not found in college registry.");
            }
            return "Rahul Sharma";
        }
    }

    try {
        $service = new StudentService();
        $student = $service->findStudent(999);
    } catch (StudentNotFoundException $e) {
        echo "Notice: " . $e->getMessage();
    }
?>

BCA / CS University Exam Corner

Interactive Student Practice Session