Programmatic configuration of slf4j/logback

Now I have experience with programmatic configuration of slf4j/logback.
Task
A program must open separate log file for each processed input file.
Solution for task
Instead of configuring logback via xml, the one needs to “manually” instantiate encoders, appenders and loggers, then configure and link them together.
Caveat 1
Logback goes crazy on attempt to share encoder (i.e. PatternLayoutEncoder) between appenders.
Solution for caveat 1
Create separate encoder for each appender.
Caveat 2
Logback refuses to log anything, if encoders and appenders are not associated with logging context.
Solution for caveat 2
Call setContext on each encoder and appender, passing LoggerFactory as a parameter.
Caveat 3
Logback refuses to log anything, if encoders and appenders are not started.
Solution for caveat 3
encoders and appenders need to be started in the correct order, i.e. first encoders, then appenders.
Caveat 4
RollingPolicy objects (i.e. TimeBasedRollingPolicy) produce strange error messages like “date format not recognized”, when they are not attached to the same context as appender.
Solutin for caveat 4
call setContext on RollingPolicy same way as on encoders and appenders.

Here is working example of “manual” logback configuration:

	package testpackage
	import ch.qos.logback.classic.Level
	import ch.qos.logback.classic.Logger
	import ch.qos.logback.classic.LoggerContext
	import ch.qos.logback.classic.encoder.PatternLayoutEncoder
	import ch.qos.logback.core.ConsoleAppender
	import ch.qos.logback.core.rolling.RollingFileAppender
	import ch.qos.logback.core.rolling.TimeBasedRollingPolicy
	import org.slf4j.LoggerFactory
	class TestLogConfig {
	public static void main(String[] args) {
	LoggerContext logCtx = LoggerFactory.getILoggerFactory()
	PatternLayoutEncoder logEncoder = new PatternLayoutEncoder()
	logEncoder.setContext(logCtx)
	logEncoder.setPattern('%-12date{YYYY-MM-dd HH:mm:ss.SSS} %-5level – %msg%n')
	logEncoder.start()
	ConsoleAppender logConsoleAppender = new ConsoleAppender()
	logConsoleAppender.setContext(logCtx)
	logConsoleAppender.setName('console')
	logConsoleAppender.setEncoder(logEncoder)
	logConsoleAppender.start()
	logEncoder = new PatternLayoutEncoder()
	logEncoder.setContext(logCtx)
	logEncoder.setPattern('%-12date{YYYY-MM-dd HH:mm:ss.SSS} %-5level – %msg%n')
	logEncoder.start()
	RollingFileAppender logFileAppender = new RollingFileAppender()
	logFileAppender.setContext(logCtx)
	logFileAppender.setName('logFile')
	logFileAppender.setEncoder(logEncoder)
	logFileAppender.setAppend(true)
	logFileAppender.setFile('logs/logfile.log')
	TimeBasedRollingPolicy logFilePolicy = new TimeBasedRollingPolicy()
	logFilePolicy.setContext(logCtx)
	logFilePolicy.setParent(logFileAppender)
	logFilePolicy.setFileNamePattern('logs/logfile-%d{yyyy-MM-dd_HH}.log')
	logFilePolicy.setMaxHistory(7)
	logFilePolicy.start()
	logFileAppender.setRollingPolicy(logFilePolicy)
	logFileAppender.start()
	Logger log = logCtx.getLogger("Main")
	log.additive = false
	log.level = Level.INFO
	log.addAppender(logConsoleAppender)
	log.addAppender(logFileAppender)
	}
	}

view raw

TestLogConfig.groovy

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My conclusion: logback is much easier to configure via XML. “Manual” configuration is rather tedious task and should be avoided, unless it is dictated by project needs.

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