String Interpolation

You may be familiar with Scala’s string interpolation, using the s interpolator.

With Blindsight, you can log statements as strings using the st interpolator. This creates a complete Statement that can be used in logging. The st interpolator has full support for Markers, Arguments, and exceptions, and will create an SLF4J parameterized message as the Message.

Usage

To use the st interpolator, you must import the package object, which you can do with a wildcar import:

import com.tersesystems.blindsight._

Messages

Plain messages work just as you’d expect.

val statement: Statement = st"This is a plain message"
logger.info(statement)

Markers

Using Markers has a few special cases. There can only be one Markers instance in the message, and it must come before any arguments or exceptions. The marker is not parameterized in the message.

You should use the ${markers} form when interpolating, as this prevents any leading whitespace in the message.

val marker1 = org.slf4j.MarkerFactory.getMarker("MARKER1")
val markers = Markers(marker1)
val statement: Statement = st"${markers}This is a message with a marker."
logger.info(statement)

If you have more than one marker, you can collate them in situ:

logger.info(st"${Markers(marker1) + Markers(marker2)}a single Markers will compile")

Arguments

You can have multiple Argument instances in the message. The interpolator will swap out the argument for the {} placeholder in the parameterized string, and roll them up into an Arguments instance.

In practice, you will be passing in either basic types or instances that have a ToArgument type class instance.

val dayOfWeek = "Monday"
val temp = 72 
val statement: Statement = st"It is ${dayOfWeek} and the temperature is ${temp} degrees."
logger.info(statement)

This works in conjunction with the DSL:

import DSL._
logger.info(st"Time since epoch is ${bobj("instant_tse" -> Instant.now.toEpochMilli)}")

Exceptions

You can pass an exception in anywhere in the statement, and the interpolator will create a toString argument and pass the exception as the last argument, as per the SLF4J parameterized exception guidelines.

val throwable = new IllegalStateException("illegal state")
logger.info(st"this is an $throwable")

You can pass in multiple exceptions. The last exception seen will be passed in as the designated throwable.

val ex1 = new IllegalStateException("ex1")
val ex2 = new IllegalStateException("ex2")
val ex3 = new IllegalStateException("ex3")
logger.info(st"$ex1 $ex2 $ex3") // ex3 will be chosen as the exception.