## Filters Filtering is a mechanism which allows the user to configure more precisely which logging events will be logged by an appender, and which will be ignored. Multiple filters can be defined on any appender; they will form a filter chain. When a logging event is passed onto an appender, the event will first pass through the filter chain. Each filter in the chain will examine the logging event and make a decision to either: ACCEPT the logging event - The event will be logged without consulting the remaining filters in the chain. DENY the logging event - The event will be not logged without consulting the remaining filters in the chain. Remain NEUTRAL - No decision is made, therefore the next filter in the chain is consulted. If there are no remaining filters in the chain, the event is logged. ### Configuring filters Filters are configurable in the XML and PHP configuration format. They cannot be configured using the properties configuration format. Like appenders and layouts, depending on the class used, filters may have configurable parameters which determine their behaviour. Here is a configuration example: XML PHP
    <configuration xmlns="http://logging.apache.org/log4php/">
        <appender name="defualt" class="LoggerAppenderEcho">
            <layout class="LoggerLayoutSimple"/>
            <filter class="LoggerFilterStringMatch">
                <param name="stringToMatch" value="interesting" />
                <param name="acceptOnMatch" value="true" />
            </filter>
            <filter class="LoggerFilterLevelRange">
                <param name="levelMin" value="debug" />
                <param name="levelMax" value="error" />
            </filter>
        </appender>
        <root>
            <level value="TRACE" />
            <appender_ref ref="defualt" />
        </root>
    </configuration>
    array(
        'appenders' => array(
            'default' => array(
                'class' => 'LoggerAppenderEcho'
                'layout' => array(
                    'class' => 'LoggerLayoutSimple'
                ),
                'filters' => array(
                    array(
                        'class' => 'LoggerFilterStringMatch',
                        'params' => array(
                            'stringToMatch' => 'interesting',
                            'acceptOnMatch' => true,
                        )
                    ),
                    array(
                        'class' => 'LoggerFilterLevelRange',
                        'params' => array(
                            'levelMin' => 'debug',
                            'levelMax' => 'error',
                        )
                    )
                )
            )
        ),
        'rootLogger' => array(
        	'appenders' => array('default'),
        )
    )
In this example, there are two filters defined for the default appender. The first filter `LoggerFilterStringMatch` searches for the string "interesting" in the logging event's message. If the string is found, the filter will ACCEPT the logging event, and the event will be logged. If the string is not found, the filter will remain NEUTRAL, and the event will be passed on to the next filter. The second filter `LoggerFilterLevelRange` ACCEPTS all events which have a level between DEBUG and ERROR (in other words, levels DEBUG, INFO, WARN and ERROR). It DENIES all other events. Therefore, this filter configuration will log events which which have a level between DEBUG and ERROR, except of theose which have the string "interesting" in the message. Those will be logged regardless of their level. ### Filter reference The following filters are available in log4php:
Name | Destination
--- | ---
LoggerFilterDenyAll | Denies all logging events.
LoggerFilterLevelMatch | Filters based on logging event level.
LoggerFilterLevelRange | Filters based on logging event level range.
LoggerFilterStringMatch | Filters by searching for a string in the logging event message.
### LoggerFilterDenyAll This filters simply denies all logging events. It has no configurable parameters. ### LoggerFilterLevelMatch This filter either accepts the specified logger level or denies it. #### Configurable parameters
Parameter | Type | Required | Default | Description
--- | --- | --- | --- | ---
levelToMatch | LoggerLevel | Yes | - | The level to match
acceptOnMatch | boolean | No | true | If true, the matching log level is accepted, denied otherwise.
#### Example The following filter configuration will deny all logging events with level DEBUG. It will remain neutral for others.
    <filter class="LoggerFilterLevelMatch">
        <param name="levelToMatch" value="debug" />
        <param name="acceptOnMatch" value="false" />
    </filter>
### LoggerFilterLevelRange This filter accepts or denies logging events if their log level is within the specified range. #### Configurable parameters
Parameter | Type | Required | Default | Description
--- | --- | --- | --- | ---
levelMin | LoggerLevel | Yes | - | The minimum level to log. If set, levels lower than this will be denied.
levelMax | LoggerLevel | Yes | - | The maximum level to log. If set, levels higher than this will be denied.
acceptOnMatch | boolean | No | true | If true, the matching log level is accepted, denied otherwise.
#### Example The following filter configuration denies levels greater than WARN.
    <filter class="LoggerFilterLevelRange">
        <param name="levelMax" value="warn" />
        <param name="acceptOnMatch" value="false" />
    </filter>
### LoggerFilterStringMatch This filter allows or denies logging events if their message contains a given string. #### Configurable parameters
Parameter | Type | Required | Default | Description
--- | --- | --- | --- | ---
stringToMatch | LoggerLevel | Yes | - | The level to match
levelMax | LoggerLevel | Yes | - | The level to match
acceptOnMatch | boolean | No | true | If true, the matching log level is accepted, denied otherwise.
#### Example The following filter configuration denies events which contain the string "not-interesting" in their message.
    <filter class="LoggerFilterStringMatch">
        <param name="StringToMatch" value="not-interesting" />
        <param name="AcceptOnMatch" value="false" />
    </filter>