org.apache.log4j.spi
Class Filter

java.lang.Object
  org.apache.log4j.spi.Filter

All Implemented Interfaces:

OptionHandler

Direct Known Subclasses:

DenyAllFilter, LevelMatchFilter, LevelRangeFilter, StringMatchFilter

public abstract class Filter
extends Object
implements OptionHandler

Users should extend this class to implement customized logging event filtering. Note that Category and AppenderSkeleton, the parent class of all standard appenders, have built-in filtering rules. It is suggested that you first use and understand the built-in rules before rushing to write your own custom filters.

This abstract class assumes and also imposes that filters be organized in a linear chain. The decide(LoggingEvent) method of each filter is called sequentially, in the order of their addition to the chain.

The decide(LoggingEvent) method must return one of the integer constants DENY, NEUTRAL or ACCEPT.

If the value DENY is returned, then the log event is dropped immediately without consulting with the remaining filters.

If the value NEUTRAL is returned, then the next filter in the chain is consulted. If there are no more filters in the chain, then the log event is logged. Thus, in the presence of no filters, the default behaviour is to log all logging events.

If the value ACCEPT is returned, then the log event is logged without consulting the remaining filters.

The philosophy of log4j filters is largely inspired from the Linux ipchains.

Note that filtering is only supported by the DOMConfigurator. The PropertyConfigurator does not support filters.

Since:

0.9.0

Author:

Ceki Gülcü

Field Summary

static int	ACCEPT The log event must be logged immediately without consulting with the remaining filters, if any, in the chain.
static int	DENY The log event must be dropped immediately without consulting with the remaining filters, if any, in the chain.
static int	NEUTRAL This filter is neutral with respect to the log event.
Filter	next Points to the next filter in the filter chain.

Constructor Summary

Filter()

Method Summary

void	activateOptions() Usually filters options become active when set.
abstract int	decide(LoggingEvent event) If the decision is DENY, then the event will be dropped.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

next

public Filter next

Points to the next filter in the filter chain.

DENY

public static final int DENY

The log event must be dropped immediately without consulting with the remaining filters, if any, in the chain.

See Also:

Constant Field Values

NEUTRAL

public static final int NEUTRAL

This filter is neutral with respect to the log event. The remaining filters, if any, should be consulted for a final decision.

See Also:

Constant Field Values

ACCEPT

public static final int ACCEPT

The log event must be logged immediately without consulting with the remaining filters, if any, in the chain.

See Also:

Constant Field Values

Constructor Detail

Filter

public Filter()

Method Detail

activateOptions

public void activateOptions()

Usually filters options become active when set. We provide a default do-nothing implementation for convenience.

Specified by:

activateOptions in interface OptionHandler

decide

public abstract int decide(LoggingEvent event)

If the decision is DENY, then the event will be dropped. If the decision is NEUTRAL, then the next filter, if any, will be invoked. If the decision is ACCEPT then the event will be logged without consulting with other filters in the chain.

Parameters:

event - The LoggingEvent to decide upon.

Returns:

decision The decision of the filter.