In this post, I am going to explain how to attach a custom filter to an appender.
Step 1: Define custom filter by extending AbstractMatcherFilter class.
public class InfoAndErrorFilter extends AbstractMatcherFilter {
@Override
public FilterReply decide(Object event) {
if (!isStarted()) {
return FilterReply.NEUTRAL;
}
LoggingEvent loggingEvent = (LoggingEvent) event;
List<Level> eventsToKeep = Arrays.asList(Level.INFO, Level.ERROR);
if (eventsToKeep.contains(loggingEvent.getLevel())) {
return FilterReply.ACCEPT;
} else {
return FilterReply.DENY;
}
}
}
Above filter accept only INFO and ERROR messages.
Step 2: Attach the filter to an appender.
<appender name="d1" class="ch.qos.logback.core.FileAppender">
<file>${LOG_FILES_HOME}/d1.log</file>
<filter class="com.sample.app.filter.InfoAndErrorFilter" />
<encoder>
<pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n
</pattern>
</encoder>
</appender>
Find the below working application.
Step 1: Create new maven project ‘logback-attach-custom-filter-to-appender’.
Step 2: Update pom.xml with maven dependencies.
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sample.app</groupId>
<artifactId>logback-attach-custom-filter-to-appender</artifactId>
<version>1</version>
<dependencies>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.10</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.2.10</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.36</version>
</dependency>
</dependencies>
</project>
Step 3: Define logback.xml file under src/main/resources folder.
logback.xml
<configuration scan="true" scanPeriod="15 seconds">
<property name="LOG_FILES_HOME" value="/Users/Shared/logback" />
<appender name="d1" class="ch.qos.logback.core.FileAppender">
<file>${LOG_FILES_HOME}/d1.log</file>
<filter class="com.sample.app.filter.InfoAndErrorFilter" />
<encoder>
<pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n
</pattern>
</encoder>
</appender>
<appender name="STDOUT"
class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
</pattern>
</encoder>
</appender>
<logger name="com.sample.app" level="INFO">
<appender-ref ref="d1" />
</logger>
<root level="INFO">
<appender-ref ref="STDOUT" />
</root>
</configuration>
Step 4: Define InfoAndErrorFilter class.
InfoAndErrorFilter.java
package com.sample.app.filter;
import java.util.Arrays;
import java.util.List;
import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.spi.LoggingEvent;
import ch.qos.logback.core.filter.AbstractMatcherFilter;
import ch.qos.logback.core.spi.FilterReply;
public class InfoAndErrorFilter extends AbstractMatcherFilter {
@Override
public FilterReply decide(Object event) {
if (!isStarted()) {
return FilterReply.NEUTRAL;
}
LoggingEvent loggingEvent = (LoggingEvent) event;
List<Level> eventsToKeep = Arrays.asList(Level.INFO, Level.ERROR);
if (eventsToKeep.contains(loggingEvent.getLevel())) {
return FilterReply.ACCEPT;
} else {
return FilterReply.DENY;
}
}
}
Step 5: Define HelloWorld class.
HelloWorld.java
package com.sample.app;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class HelloWorld {
private static Logger logger = LoggerFactory.getLogger(HelloWorld.class);
public static void main(String[] args) {
logger.trace("Trace message");
logger.debug("Debug message");
logger.info("Info message");
logger.warn("Warning message");
logger.error("Error message");
}
}
Total project structure looks like below.
Total project structure looks like below.
12:53:45.578 [main] INFO com.sample.app.HelloWorld - Info message 12:53:45.580 [main] WARN com.sample.app.HelloWorld - Warning message 12:53:45.580 [main] ERROR com.sample.app.HelloWorld - Error message
Query the contents of d1.log to confirm filtering logic.
$pwd
/Users/Shared/logback
$
$ls
d1.log
$
$cat d1.log
2022-02-23 12:53:45,578 INFO [main] c.s.a.HelloWorld [HelloWorld.java:13] Info message
2022-02-23 12:53:45,580 ERROR [main] c.s.a.HelloWorld [HelloWorld.java:15] Error message
You can download complete working application from below link.
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