How to add logging to an abstract class in php

Working on a class library I´d like to add logging to a number of classes. I use Psr\Log\LoggingInterface to give the classes access to a logger object. But how do I set the logger in all classes in a decent way. There is a dependency to the logger as it is being used everywhere in the classes

I can use

Constructor

Add the logger to the constructor with

public function __constructor (
  readonly \Psr\Log\LoggingInterface $logger = new \Psr\Log\NullLoger()
);

Setlogger

Use a public setLogger()

public function setLogger( \Psr\Log\LoggingInterface $logger ): self
{
  $this->logger = $logger;
  return $this;
}
private \Psr\Log\LoggingInterface $logger;
public function __constructor()
{
  ...
  // Make sure a logger is set
  $this->logger = new \Psr\Log\NullLogger();
  ...
}

What would be the best way to do this? Is there a better way.

+22

rj

One way to achieve this is by using Dependency Injection to inject the logger into the classes that need it. Here's an example of how you can do this:

Define an interface for your logger:

<?php

namespace YourNamespace;

use Psr\Log\LoggerInterface;

interface LoggerAwareInterface
{
    public function setLogger(LoggerInterface $logger);
}

Implement this interface in the classes that need logging:

<?php

namespace YourNamespace;

use Psr\Log\LoggerInterface;

class MyClass implements LoggerAwareInterface
{
    protected $logger;

    public function setLogger(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    // Your class methods here...
}

When instantiating your classes, inject the logger:

<?php

use Psr\Log\LoggerInterface;

class YourClassFactory
{
    protected $logger;

    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    public function createClassWithLogger()
    {
        $class = new MyClass();
        if ($class instanceof LoggerAwareInterface) {
            $class->setLogger($this->logger);
        }
        return $class;
    }
}

Finally, you can use a factory to instantiate your classes and inject the logger:

<?php

use Psr\Log\LoggerInterface;

class YourLibrary
{
    protected $logger;

    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    public function createClassInstance()
    {
        $factory = new YourClassFactory($this->logger);
        return $factory->createClassWithLogger();
    }
}

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