log/slog - Go 中 JSON 式日志实现

package main

import (
    "log/slog"
    "os"
)

func main() {
    // JSON 格式输出到 stdout
    logger := slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
        Level: slog.LevelDebug, // Level 为 Debug
    }))

    logger.Debug("DEBUG LOG")
    logger.Info("INFO LOG")
    logger.Warn("WARN LOG")
    logger.Error("ERROR LOG:", "err", "some error")

    logger.Info("INFO", "qwerty", "1.2.3.4")
}

{"time":"2009-11-10T23:00:00Z","level":"DEBUG","msg":"DEBUG LOG"}
{"time":"2009-11-10T23:00:00Z","level":"INFO","msg":"INFO LOG"}
{"time":"2009-11-10T23:00:00Z","level":"WARN","msg":"WARN LOG"}
{"time":"2009-11-10T23:00:00Z","level":"ERROR","msg":"ERROR LOG:","err":"some error"}
{"time":"2009-11-10T23:00:00Z","level":"INFO","msg":"INFO","qwerty":"1.2.3.4"}

f, err := os.OpenFile("app.json.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o644)
if err != nil {
    log.Fatal(err)
}
defer f.Close()

mw := io.MultiWriter(os.Stdout, f) // 一份数据写两处

logger := slog.New(slog.NewJSONHandler(mw, &slog.HandlerOptions{
    Level: slog.LevelInfo,
}))
slog.SetDefault(logger)
slog.Debug("THIS DEBUG INFO WILL APPEAR ON CONSOLE AND THE FILE")
slog.Info("THIS INFO WILL APPEAR ON CONSOLE AND THE FILE")
slog.Warn("THIS WARN WILL APPEAR ON CONSOLE AND THE FILE")
slog.Error("THIS ERROR WILL APPEAR ON CONSOLE AND THE FILE")

$ go run play.go;echo '- - -';cat app.json.log;rm app.json.log

go: warning: ignoring go.mod in $GOPATH /home/linserin/go
{"time":"2026-09-25T22:39:22.695105808+08:00","level":"INFO","msg":"THIS INFO WILL APPEAR ON CONSOLE AND THE FILE"}
{"time":"2026-09-25T22:39:22.695390094+08:00","level":"WARN","msg":"THIS WARN WILL APPEAR ON CONSOLE AND THE FILE"}
{"time":"2026-09-25T22:39:22.695416368+08:00","level":"ERROR","msg":"THIS ERROR WILL APPEAR ON CONSOLE AND THE FILE"}
- - -
{"time":"2026-09-25T22:39:22.695105808+08:00","level":"INFO","msg":"THIS INFO WILL APPEAR ON CONSOLE AND THE FILE"}
{"time":"2026-09-25T22:39:22.695390094+08:00","level":"WARN","msg":"THIS WARN WILL APPEAR ON CONSOLE AND THE FILE"}
{"time":"2026-09-25T22:39:22.695416368+08:00","level":"ERROR","msg":"THIS ERROR WILL APPEAR ON CONSOLE AND THE FILE"}