Apache log4php - Quick start

Quick start

You may also like to read the introduction chapter to familiarise yoursef with the basic concepts used throughout the documentation and examples.

A trivial example

Just want logging to stdout?

include('Logger.php');
$logger = Logger::getLogger("main");
$logger->info("This is an informational message.");
$logger->warn("I'm not feeling so good...");

This produces the following output:

INFO - This is an informational message.
WARN - I'm not feeling so good...

A simple example

This example shows how to configure log4php using an XML configuration file. The framework will be configured to log messages to a file, but only those with level greater or equal to WARN.

First, create a configuration file named config.xml containing:

<configuration xmlns="http://logging.apache.org/log4php/">
    <appender name="myAppender" class="LoggerAppenderFile">
        <param name="file" value="myLog.log" />
    </appender>
    <root>
        <level value="WARN" />
        <appender_ref ref="myAppender" />
    </root>
</configuration>

This configuration file does the following:

line 2: Creates an appender named myAppender using appender class LoggerAppenderFile which is used for logging to a file.
line 3: Sets the file parameter, which tells the appender to which file to write.
line 6: Sets the root logger level to WARN. This means that logging requests with the level lower than WARN will not be logged by the root logger.
line 7: Links myAppender to the root logger so that all events recieved by the root logger will be forwarded to myAppender and written into the log file.

To try it out, run the following code:

// Insert the path where you unpacked log4php
include('log4php/Logger.php');

// Tell log4php to use our configuration file.
Logger::configure('config.xml');

// Fetch a logger, it will inherit settings from the root logger
$log = Logger::getLogger('myLogger');

// Start logging
$log->trace("My first message.");   // Not logged because TRACE < WARN
$log->debug("My second message.");  // Not logged because DEBUG < WARN
$log->info("My third message.");    // Not logged because INFO < WARN
$log->warn("My fourth message.");   // Logged because WARN >= WARN
$log->error("My fifth message.");   // Logged because ERROR >= WARN
$log->fatal("My sixth message.");   // Logged because FATAL >= WARN

This will create a file named myLog.log containing the following output:

WARN - My fourth message.
ERROR - My fifth message.
FATAL - My sixth message.

An advanced example

This example covers named loggers, layouts and best practices in object-oriented programming.

Create a configuration file named config.xml with the following content:

<configuration xmlns="http://logging.apache.org/log4php/">

    <appender name="myConsoleAppender" class="LoggerAppenderConsole" />
    
    <appender name="myFileAppender" class="LoggerAppenderFile">
        <layout class="LoggerLayoutPattern">
            <param name="conversionPattern" value="%date [%logger] %message%newline" />
        </layout>
        <param name="file" value="myLog.log" />
    </appender>

    <logger name="Foo">
        <appender_ref ref="myFileAppender" />
    </logger>
    
    <root>
        <level value="DEBUG" />
        <appender_ref ref="myConsoleAppender" />
    </root>
</configuration>

The configuration defines two appenders: one writes to the console, and the other to a file.

The console appender doesn't have a layout defined, so it will revert to default layout (LoggerLayoutSimple). The file appender uses a different layout (LoggerLayoutPattern) which will result in different formatting of the logging events.

The console appender is linked to the root logger. The file appender is linked to the logger named Foo, however Foo also inherits appenders from the root logger (in this case the console appender). This means that logging events sent to the Foo logger will be logged both to the console and the file.

Consider the following code snippet:

// Include and configure log4php
include('log4php/Logger.php');
Logger::configure('config.xml');

/**
 * This is a classic usage pattern: one logger object per class.
 */
class Foo
{
    /** Holds the Logger. */
    private $log;

    /** Logger is instantiated in the constructor. */
    public function __construct()
    {
        // The __CLASS__ constant holds the class name, in our case "Foo".
        // Therefore this creates a logger named "Foo" (which we configured in the config file)
        $this->log = Logger::getLogger(__CLASS__);
    }

    /** Logger can be used from any member method. */
    public function go()
    {
        $this->log->info("We have liftoff.");
    }
}

$foo = new Foo();
$foo->go();

This produces the following output in the console:

INFO - We have liftoff.

And the following in the log file:

01/06/11 18:43:39,545 [5428] INFO Foo - We have liftoff.

Note the different layout, this is because LoggerLayoutTTCC was used as layout for the file appender.