CodeGym/Java Course/Module 3. Java Professional/Log filters in Log4j

Log filters in Log4j

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5.1 List of filters

The logger allows you to very coolly configure message filtering. To do this, he has a couple of dozen filters with all sorts of parameters. The table below shows the most popular ones.

	Filters	Description
1	BurstFilter	Allows you to control the frequency of messages per second for a given logging level.
2	CompositeFilter	Allows you to set multiple sequential filters.
3	DynamicThresholdFilter	Allows you to enable detailed logging if certain information is found in the log.
4	MapFilter	Allows you to build a complex logical expression for the filter from several parameters.
5	MarkerFilter	Allows you to filter messages by tags, the tag must first be added during the event logging.
6	RegexFilter	Allows you to set a mask - a regular expression.
7	StructuredDataFilter	Allows you to filter messages by the presence of certain data in them.
8	ThreadContextMapFilter	Allows you to manage filters based on data taken from the context of the current thread.
9	ThresholdFilter	Controls logging based on the log message level.
10	TimeFilter	Allows you to turn filters on and off at specific times.

Below we will talk about just three of them. You can learn more about these filters on their official website .

5.2 TimeFilter

The filter TimeFilterallows you to turn filters on and off at a certain time, it has 5 parameters:


1	start	Logging start time in the format`HH:mm:ss`
2	end	Logging off time in the format`HH:mm:ss`
3	timezone	Sets the time zone.
4	onMatch	How to log if filter condition is true . Maybe `ACCEPT`, `DENY`or `NEUTRAL`. Default `NEUTRAL`.
5	onMismatch	How to log if filter condition is false . Maybe `ACCEPT`, `DENY`or `NEUTRAL`. Default `NEUTRAL`.

Let's set up a filter that will turn on logging at 5am and turn it off at 5:30am every day. An example with a complete filter configuration is below:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
<Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log" filePattern="logs/app-%d{MM-dd-yyyy}.log.gz">
    <TimeFilter start="05:00:00" end="05:30:00" onMatch="ACCEPT" onMismatch="DENY"/>
    <PatternLayout>
        <pattern>%d %p %c{1.} [%t] %m%n</pattern>
    </PatternLayout>
    <TimeBasedTriggeringPolicy />
    </RollingFile>
</Appenders>
<Loggers>
    <Root level="error">
    <AppenderRef ref="RollingFile"/>
    </Root>
</Loggers>
</Configuration>

5.3 RegexFilter

The filter RegexFilterallows you to set a mask (regular expression) for filtering messages. This filter has 4 parameters:


1	regex	Specifies a regular expression - a mask that is used to filter messages.`HH:mm:ss`
2	useRawMsg	The mask is applied in the message before formatting (true) or after formatting (false)
3	onMatch	How to log if filter condition is true . Maybe `ACCEPT`, `DENY`or `NEUTRAL`. Default `NEUTRAL`.
4	onMismatch	How to log if filter condition is false . Maybe `ACCEPT`, `DENY`or `NEUTRAL`. Default `NEUTRAL`.

Let's set up a filter that will only allow messages containing the word codegym. An example with a complete filter configuration is below:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
<Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"   filePattern="logs/app-%d{MM-dd-yyyy}.log.gz">
    <RegexFilter regex=".* codegym .*" onMatch="ACCEPT" onMismatch="DENY"/>
    <PatternLayout>
        <pattern>%d %p %c{1.} [%t] %m%n</pattern>
    </PatternLayout>
    <TimeBasedTriggeringPolicy />
    </RollingFile>
  </Appenders>
<Loggers>
    <Root level="error">
    <AppenderRef ref="RollingFile"/>
    </Root>
</Loggers>
</Configuration>

5.4 ThresholdFilter

The ThresholdFilter filter allows you to configure filtering by message level. It has only 3 parameters:


1	level	Sets the name of the message logging level: `ERROR`, `DEBUG`, …
2	onMatch	How to log if filter condition is true . Maybe `ACCEPT`, `DENY`or `NEUTRAL`. Default `NEUTRAL`.
3	onMismatch	How to log if filter condition is false . Maybe `ACCEPT`, `DENY`or `NEUTRAL`. Default `NEUTRAL`.

Let's set up a filter that will only allow messages of level DEBUG. An example with a complete filter configuration is below:

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
<Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log" filePattern="logs/app-%d{MM-dd-yyyy}.log.gz">
       <ThresholdFilter level="DEBUG" onMatch="ACCEPT" onMismatch="DENY"/>
    <PatternLayout>
        <pattern>%d %p %c{1.} [%t] %m%n</pattern>
    </PatternLayout>
    <TimeBasedTriggeringPolicy />
    </RollingFile>
</Appenders>
<Loggers>
    <Root level="error">
    <AppenderRef ref="RollingFile"/>
    </Root>
</Loggers>
</Configuration>