Apache log4php - Appenders

Appenders

Logging requests can be sent to multiple destinations, such as files, databases, syslog and others. Such destinations are called appenders. Appenders are attached to loggers and each logger can have multiple attached appenders.

Appender reference

The following appender classes are available:

Name	Destination
LoggerAppenderConsole	Console, directly to the stdout or stderr stream.
LoggerAppenderEcho	Console, using the PHP `echo` command.
LoggerAppenderFile	A file.
LoggerAppenderDailyFile	A file (new file each day).
LoggerAppenderRollingFile	A file (new file when a specified size has been reached).
LoggerAppenderMail	Sends the log via email. The entire log is sent in one email.
LoggerAppenderMailEvent	Sends the log via email. Each log entry is sent in individual emails.
LoggerAppenderMongoDB	MongoDB.
LoggerAppenderNull	Ignores all log events.
LoggerAppenderPDO	Database.
LoggerAppenderPhp	Creates a PHP user-level message using the PHP `trigger_error()` function.
LoggerAppenderSocket	A network socket.
LoggerAppenderSyslog	Syslog.

Configuring appenders

The following configuration shows how to configure an appender which logs to a file:

<configuration xmlns="http://logging.apache.org/log4php/">
    <appender name="default" class="LoggerAppenderFile">
        <layout class="LoggerLayoutSimple" />
        <param name="file" value="/var/log/my.log" />
        <param name="append" value="true" />
    </appender>
    <root>
        <appender_ref ref="default" />
    </root>
</configuration>

From the configuration you can see that an appender has the following properties:

A name which uniquely identifies it, in this case default.
A class which specifies which appender class will be used to handle the requests. Since we wish to log to a file, LoggerAppenderFile is used in this case.
A layout which transforms the logging events to string which can be logged. A layout is required by most appenders, but some do not require it, such as the database appender. If a layout is not defined, the appenders will use a default layout.
Zero or more parameters which configure the appender behaviour. In this example, the file parameter governs the path to the file which will be used for logging, and append defines that log messages should be appended to the file, instead of truncating it.

Linking appenders to loggers

A logger can be linked to one or more appenders. Also, multiple loggers can share the same appender.

Consider the following configuration:

<log4php:configuration xmlns:log4php="http://logging.apache.org/log4php/">
    <appender name="primus" class="LoggerAppenderConsole" />
    <appender name="secundus" class="LoggerAppenderFile">
        <param name="file" value="/var/log/my.log" />
    </appender>
    <logger name="main">
        <appender_ref ref="primus" />
        <appender_ref ref="secundus" />
    </logger>
    <logger name="alternative">
        <appender_ref ref="primus" />
    </logger>
</log4php:configuration>

This configures two appenders, called primus and secundus, and two loggers named main and alternative. The logger main is linked to primus and secundus and will therefore forward logging events to both of them. In other words, it will log both to console and to a file. Logger alternative is only linked to appender primus and will therefore only log to the console.

Appender threshold

An appender can be assigned a threshold level. All logging requests with level lower than this threshold will be ignored.

For example, if you set WARN as a threshold, then INFO, DEBUG and TRACE level events recieved by the appender will not be logged, but WARN, ERROR and FATAL will.

An example of setting an appender threshold:

<configuration xmlns="http://logging.apache.org/log4php/">
    <appender name="default" class="LoggerAppenderEcho" threshold="WARN" />
    <root>
        <appender_ref ref="default" />
    </root>
</configuration>