Programatically set ByteArrayOutputStream appender for logback logger in scala

setLogbackAppender.scala

// this was driving me crazy, so here we are, for everyone.
// inspiration from https://stackoverflow.com/questions/19058722/creating-an-outputstreamappender-for-logback

import ch.qos.logback.classic.Logger
import ch.qos.logback.classic.LoggerContext
import ch.qos.logback.classic.encoder.PatternLayoutEncoder
import ch.qos.logback.classic.spi.ILoggingEvent
import ch.qos.logback.core.OutputStreamAppender
import org.slf4j.LoggerFactory

import scala.collection.JavaConverters._

// .... somewhere in your code ....

    // get your logger
    val log = LoggerFactory.getLogger("....").asInstanceOf[Logger]

    val ctx = LoggerFactory.getILoggerFactory.asInstanceOf[LoggerContext]
    val encoder = new PatternLayoutEncoder()  // this is mandatory. Without that, nothing happens silently
    encoder.setContext(ctx)                   // order of setters matters
    encoder.setPattern("%msg%n")              // and if you miss that... nothing happens silently
    encoder.start()                           // don't forget start!

    val os = new ByteArrayOutputStream()
    val appender = new OutputStreamAppender[ILoggingEvent]()
    appender.setImmediateFlush(true)
    appender.setName("test-byte-array")
    appender.setContext(ctx)                  // context must be set first
    appender.setEncoder(encoder)              // then encoder
    appender.setOutputStream(os)              // then output stream
    appender.start()                          // don't forget start!

    // if you want to remove other appenders
    log.iteratorForAppenders().asScala.foreach { a =>
      log.detachAppender(a)
      a.stop()
    }

    log.setAdditive(false) // disable root logger/appender
    // actually add you new appender
    log.addAppender(appender)

    // exec ...
    log.error("ohno! An error!")
 
    val output = os.toString(StandardCharsets.UTF_8)