In this article, we'll create a simple logger system using the Singleton Pattern in PHP.
This logger will allow you to log messages to a file, ensuring that there is only one instance of the logger throughout your application.
Step-by-Step Implementation
Step 1: Create the Logger Class
We'll start by defining a Logger class that follows the Singleton Pattern. This class will have methods for logging messages and ensuring that only one instance exists.
class Logger {
private static ?Logger $instance = null;
private string $logFile;
// Private constructor to prevent direct instantiation
private function __construct() {
$this->logFile = 'app.log'; // Define the log file
}
// Method to get the single instance of Logger
public static function getInstance(): Logger {
if (self::$instance === null) {
self::$instance = new Logger();
}
return self::$instance;
}
// Method to log a message
public function log(string $message): void {
$timestamp = date('Y-m-d H:i:s');
$formattedMessage = "[$timestamp] $message" . PHP_EOL;
file_put_contents($this->logFile, $formattedMessage, FILE_APPEND);
}
// Optional: Method to read the log file (for testing purposes)
public function readLog(): string {
return file_get_contents($this->logFile);
}
}
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Step 2: Usage Example
Now that we have our Logger class set up, let's see how to use it in a real application scenario.
// Usage of the Logger
$logger = Logger::getInstance();
$logger->log("Application started.");
// Simulating some actions
$logger->log("User logged in.");
$logger->log("Error: Unable to connect to the database.");
$logger->log("Application finished.");
Step 3: Testing the Logger
You can read the log file to verify that messages are being logged correctly. Here’s a small snippet to do that:
// Displaying the log contents
$logger = Logger::getInstance();
echo $logger->readLog();
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Complete Example
Putting everything together, here’s the complete code for the Logger system.
class Logger {
private static ?Logger $instance = null;
private string $logFile;
private function __construct() {
$this->logFile = 'app.log'; // Define the log file
}
public static function getInstance(): Logger {
if (self::$instance === null) {
self::$instance = new Logger();
}
return self::$instance;
}
public function log(string $message): void {
$timestamp = date('Y-m-d H:i:s');
$formattedMessage = "[$timestamp] $message" . PHP_EOL;
file_put_contents($this->logFile, $formattedMessage, FILE_APPEND);
}
public function readLog(): string {
return file_get_contents($this->logFile);
}
}
// Usage of the Logger
$logger = Logger::getInstance();
$logger->log("Application started.");
$logger->log("User logged in.");
$logger->log("Error: Unable to connect to the database.");
$logger->log("Application finished.");
// Displaying the log contents
echo $logger->readLog();
In this hands-on exercise, we've successfully implemented a simple logger system using the Singleton Pattern in PHP. This design ensures that only one instance of the logger exists, which simplifies the logging process and avoids conflicts.
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