LogWriter

LogWriter is the sink half of console log output: it takes text that has already been formatted and pushes it to a destination — stdout, stderr, a file. Its partner is the LogFormatter, which turns a LogRecord into that text. You rarely name a writer directly — you hand a formatter/writer pair to log.writer, and the built-ins below cover the usual destinations. Reach for a custom one only to send output somewhere the built-ins don't.

trait LogWriter {
  def write(content: CharSequence): Unit
  def flush(): Unit = ()
  def close(): Unit = ()
}

write receives one fully-formatted line; flush and close default to no-ops, so a simple writer overrides only write.

Built-in Writers

Three singletons cover the common destinations:

Writer	Destination
StdoutWriter	System.out
StderrWriter	System.err
NoopWriter	Discards output — for benchmarking the formatting path

Example Usage

Pair a writer with a formatter and hand both to log.writer. It is additive — each call adds another channel, and every record is sent to all of them:

import zio.blocks.telemetry._

log.writer(TextLogFormatter, StdoutWriter)  // human-readable text to stdout
log.writer(JsonLogFormatter, StderrWriter)  // OTLP JSON to stderr

log.info("server ready", "port" -> 8080L)   // written to both channels

Custom Writer

Implement the trait to send formatted output somewhere the built-ins don't — a file, say. Override write, plus flush/close if the destination holds resources:

import zio.blocks.telemetry._
import java.io.PrintWriter

val fileWriter = new LogWriter {
  private val out = new PrintWriter("app.log")
  def write(content: CharSequence): Unit = out.println(content)
  override def flush(): Unit             = out.flush()
  override def close(): Unit             = out.close()
}

log.writer(TextLogFormatter, fileWriter)