java.util.logging bridge

It is possible to use zio-logging for included java.util.logging Loggers (do not confuse with java.platform.logging), usually third-party non-ZIO libraries (most notable: OpenTelemetry used by ZIO-telemetry). To do so, import the zio-logging-jul-bridge module

libraryDependencies += "dev.zio" %% "zio-logging-jul-bridge" % "2.4.0"

and use one of the JULBridge layers when setting up logging

import zio.logging.jul.bridge.JULBridge

program.provideCustom(JULBridge.init())

JULBridge layers:

• JULBridge.init(configPath: NonEmptyChunk[String] = logFilterConfigPath) - setup with LogFilter from filter configuration, default configuration path: logger.filter, default LogLevel is INFO
• JULBridge.init(filter: LogFilter[Any]) - setup with given LogFilter
• JULBridge.initialize - setup without filtering

Need for log filtering in JUL bridge: filtering in JUL is made on higher level than jul-bridge (on Logger level and not Handler level - which JULBridge is). Due to that the whole filtering in JUL is disabled and is implemented in JULBridge. This may cause degraded performance and much more logs when using other Handlers.

JUL logger name is stored in log annotation with key logger_name (zio.logging.loggerNameAnnotationKey), following log format

import zio.logging.jul.bridge.JULBridge
import zio.logging.LoggerNameExtractor

val loggerName = LoggerNameExtractor.loggerNameAnnotationOrTrace
val loggerNameFormat = loggerName.toLogFormat()

may be used to get logger name from log annotation or ZIO Trace.

This logger name extractor is used by default in log filter, which applying log filtering by defined logger name and level:

val logFilterConfig = LogFilter.LogLevelByNameConfig(
  LogLevel.Info,
  "zio.logging.jul  " -> LogLevel.Debug,
  "JUL-LOGGER"        -> LogLevel.Warning
)

val logFilter: LogFilter[String] = logFilterConfig.toFilter

JUL bridge with custom logger can be setup:

import zio.logging.jul.bridge.JULBridge
import zio.logging.consoleJsonLogger

val logger = Runtime.removeDefaultLoggers >>> consoleJsonLogger() >+> JULBridge.init()

Examples

You can find the source code here

JUL bridge with JSON console logger

package zio.logging.example

import zio.logging.jul.bridge.JULBridge
import zio.logging.{ConsoleLoggerConfig, LogAnnotation, LogFilter, LogFormat, LoggerNameExtractor, consoleJsonLogger}
import zio.{ExitCode, LogLevel, Runtime, Scope, ZIO, ZIOAppArgs, ZIOAppDefault, ZLayer}

import java.util.UUID

object JULBridgeExampleApp extends ZIOAppDefault {

  private val julLogger = java.util.logging.Logger.getLogger("JUL-LOGGER")

  private val logFilterConfig = LogFilter.LogLevelByNameConfig(
    LogLevel.Info,
    "zio.logging.slf4j" -> LogLevel.Debug,
    "SLF4J-LOGGER"      -> LogLevel.Warning
  )

  private val logFormat = LogFormat.label(
    "name",
    LoggerNameExtractor.loggerNameAnnotationOrTrace.toLogFormat()
  ) + LogFormat.logAnnotation(LogAnnotation.UserId) + LogFormat.logAnnotation(
    LogAnnotation.TraceId
  ) + LogFormat.default

  private val loggerConfig = ConsoleLoggerConfig(logFormat, logFilterConfig)

  override val bootstrap: ZLayer[ZIOAppArgs, Any, Any] =
    Runtime.removeDefaultLoggers >>> consoleJsonLogger(loggerConfig) >+> JULBridge.init(loggerConfig.toFilter)

  private val uuids = List.fill(2)(UUID.randomUUID())

  override def run: ZIO[Scope, Any, ExitCode] =
    for {
      _ <- ZIO.logInfo("Start")
      _ <- ZIO.foreachPar(uuids) { u =>
        ZIO.succeed(julLogger.info("Test INFO!")) *> ZIO.succeed(
          julLogger.warning("Test WARNING!")
        ) @@ LogAnnotation.UserId(
          u.toString
        )
      } @@ LogAnnotation.TraceId(UUID.randomUUID())
      _ <- ZIO.logDebug("Done")
    } yield ExitCode.success

}

Expected console output:

{"name":"zio.logging.example.JULbridgeExampleApp","timestamp":"2024-05-26T13:50:20.6832831+02:0","level":"INFO","thread":"zio-fiber-1143120685","message":"Start"}
{"name":"JUL-LOGGER","trace_id":"08e9e10a-d3c5-4f90-8627-2ae4ddee1522","timestamp":"2024-05-26T13:50:20.7112909+02:0","level":"INFO","thread":"zio-fiber-1683803358","message":"Test INFO!"}
{"name":"JUL-LOGGER","trace_id":"08e9e10a-d3c5-4f90-8627-2ae4ddee1522","timestamp":"2024-05-26T13:50:20.7112909+02:0","level":"INFO","thread":"zio-fiber-71852457","message":"Test INFO!"}
{"name":"JUL-LOGGER","user_id":"85f762cc-e62c-4576-9f14-6a3ad0918d99","trace_id":"08e9e10a-d3c5-4f90-8627-2ae4ddee1522","timestamp":"2024-05-26T13:50:20.7142882+02:0","level":"WARN","thread":"zio-fiber-1911711828","message":"Test WARNING!"}
{"name":"JUL-LOGGER","user_id":"47850c02-bb60-4b6a-9c0f-0aa095066d10","trace_id":"08e9e10a-d3c5-4f90-8627-2ae4ddee1522","timestamp":"2024-05-26T13:50:20.7142882+02:0","level":"WARN","thread":"zio-fiber-1801412106","message":"Test WARNING!"}