Log4jCollector Junit5 Extension

Log4jCollector.kt

import org.apache.logging.log4j.LogManager
import org.apache.logging.log4j.core.Filter.Result
import org.apache.logging.log4j.core.LogEvent
import org.apache.logging.log4j.core.Logger
import org.apache.logging.log4j.core.filter.AbstractFilter
import org.junit.jupiter.api.extension.AfterAllCallback
import org.junit.jupiter.api.extension.BeforeAllCallback
import org.junit.jupiter.api.extension.BeforeEachCallback
import org.junit.jupiter.api.extension.ExtensionContext

/**
 * Usage:
 *
 *  companion object {
 *    @RegisterExtension @JvmStatic
 *    val logCollector: Log4jCollector = Log4jCollector(LogManager.getLogger(...))
 *  }
 *
 */

class Log4jCollector(private val logger: Logger) : BeforeAllCallback, BeforeEachCallback, AfterAllCallback {

    val events = mutableListOf<LogEvent>()
    private val eventCollector = object : AbstractFilter() {
        override fun filter(event: LogEvent?): Result {
            event?.let { events.add(it.toImmutable()) }
            return Result.NEUTRAL
        }
    }

    constructor(logger: org.apache.logging.log4j.Logger) : this(logger as Logger)
    constructor(clazz: Class<*>?) : this(LogManager.getLogger(clazz) as Logger)
    constructor(name: String?) : this(LogManager.getLogger(name) as Logger)

    override fun beforeAll(context: ExtensionContext) {
        logger.get().addFilter(eventCollector)
    }

    override fun beforeEach(context: ExtensionContext) {
        events.clear()
    }

    override fun afterAll(context: ExtensionContext) {
        logger.get().removeFilter(eventCollector)
    }
}