Overview of Zend\Log

Zend\Log\Logger is a component for general purpose logging. It supports multiple log backends, formatting messages sent to the log, and filtering messages from being logged. These functions are divided into the following objects:

• A Logger (instance of Zend\Log\Logger) is the object that your application uses the most. You can have as many Logger objects as you like; they do not interact. A Logger object must contain at least one Writer, and can optionally contain one or more Filters.
• A Writer (inherits from Zend\Log\Writer\AbstractWriter) is responsible for saving data to storage.
• A Filter (implements Zend\Log\Filter\FilterInterface) blocks log data from being saved. A filter is applied to an individual writer. Filters can be chained.
• A Formatter (implements Zend\Log\Formatter\FormatterInterface) can format the log data before it is written by a Writer. Each Writer has exactly one Formatter.

Creating a Log

To get started logging, instantiate a Writer and then pass it to a Logger instance:

$logger = new Zend\Log\Logger;
$writer = new Zend\Log\Writer\Stream('php://output');

$logger->addWriter($writer);

It is important to note that the Logger must have at least one Writer. You can add any number of Writers using the Log’s addWriter() method.

You can also add a priority to each writer. The priority is specified as number and passed as second argument in the addWriter() method.

Another way to add a writer to a Logger is to use the name of the writer as follow:

$logger = new Zend\Log\Logger;

$logger->addWriter('stream', null, array('stream' => 'php://output'));

In this example we passed the stream php://output as parameter (as array).

Logging Messages

To log a message, call the log() method of a Log instance and pass it the message with a corresponding priority:

$logger->log(Zend\Log\Logger::INFO, 'Informational message');

The first parameter of the log() method is an integer priority and the second parameter is a string message. The priority must be one of the priorities recognized by the Logger instance. This is explained in the next section. There is also an optional third parameter used to pass extra informations to the writer’s log.

A shortcut is also available. Instead of calling the log() method, you can call a method by the same name as the priority:

$logger->log(Zend\Log\Logger::INFO, 'Informational message');
$logger->info('Informational message');

$logger->log(Zend\Log\Logger::EMERG, 'Emergency message');
$logger->emerg('Emergency message');

Destroying a Log

If the Logger object is no longer needed, set the variable containing it to NULL to destroy it. This will automatically call the shutdown() instance method of each attached Writer before the Log object is destroyed:

$logger = null;

Explicitly destroying the log in this way is optional and is performed automatically at PHP shutdown.

Using Built-in Priorities

The Zend\Log\Logger class defines the following priorities:

EMERG   = 0;  // Emergency: system is unusable
ALERT   = 1;  // Alert: action must be taken immediately
CRIT    = 2;  // Critical: critical conditions
ERR     = 3;  // Error: error conditions
WARN    = 4;  // Warning: warning conditions
NOTICE  = 5;  // Notice: normal but significant condition
INFO    = 6;  // Informational: informational messages
DEBUG   = 7;  // Debug: debug messages

These priorities are always available, and a convenience method of the same name is available for each one.

The priorities are not arbitrary. They come from the BSD syslog protocol, which is described in RFC-3164. The names and corresponding priority numbers are also compatible with another PHP logging system, PEAR Log, which perhaps promotes interoperability between it and Zend\Log\Logger.

Priority numbers descend in order of importance. EMERG (0) is the most important priority. DEBUG (7) is the least important priority of the built-in priorities. You may define priorities of lower importance than DEBUG. When selecting the priority for your log message, be aware of this priority hierarchy and choose appropriately.

Understanding Log Events

When you call the log() method or one of its shortcuts, a log event is created. This is simply an associative array with data describing the event that is passed to the writers. The following keys are always created in this array: timestamp, message, priority, and priorityName.

The creation of the event array is completely transparent.

Log PHP Errors

Zend\Log\Logger can also be used to log PHP errors and intercept Exceptions. Calling the static method registerErrorHandler($logger) will add the $logger object before the current PHP error handler, and will pass the error along as well.

$logger = new Zend\Log\Logger;
$writer = new Zend\Log\Writer\Stream('php://output');

$logger->addWriter($writer);

Zend\Log\Logger::registerErrorHandler($logger);

If you want to unregister the error handler you can use the unregisterErrorHandler() static method.

Zend\Log\Logger events from PHP errors fields matching handler ( int $errno , string $errstr [, string $errfile [, int $errline [, array $errcontext ]]] ) from set_error_handler

Name	Error Handler Parameter	Description
message	errstr	Contains the error message, as a string.
errno	errno	Contains the level of the error raised, as an integer.
file	errfile	Contains the filename that the error was raised in, as a string.
line	errline	Contains the line number the error was raised at, as an integer.
context	errcontext	(optional) An array that points to the active symbol table at the point the error occurred. In other words, errcontext will contain an array of every variable that existed in the scope the error was triggered in. User error handler must not modify error context.

You can also configure a Logger to intercept Exceptions using the static method registerExceptionHandler($logger).