golang package log学习笔记

日志是程序中必不可少的部分，golang的日志包log相当简洁明了。

函数

log包主要有以下三个系列的函数

// Print calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Print.
func Print(v ...interface{}) {
    std.Output(2, fmt.Sprint(v...))
}

// Fatal is equivalent to Print() followed by a call to os.Exit(1).
func Fatal(v ...interface{}) {
    std.Output(2, fmt.Sprint(v...))
    os.Exit(1)
}

// Panic is equivalent to Print() followed by a call to panic().
func Panic(v ...interface{}) {
    s := fmt.Sprint(v...)
    std.Output(2, s)
    panic(s)
}

• Print系列：相当与直接输出日志
• Fatal系列：输出日志后退出程序
• Panic系列： 输出日志后终止程序原有的流程，逐层往上执行panic

还有以下两个函数对日志输出格式进行设置

// SetPrefix sets the output prefix for the standard logger.
func SetPrefix(prefix string) {
    std.SetPrefix(prefix)
}

// SetFlags sets the output flags for the standard logger.
func SetFlags(flag int) {
    std.SetFlags(flag)
}

• SetPrefix：设置日志的前缀
• SetFlags：设置日志输出的抬头信息

常量

const (
        Ldate         = 1 << iota     // 日期 the date in the local time zone: 2009/01/23
        Ltime                         // 时间 the time in the local time zone: 01:23:23
        Lmicroseconds                 // 毫秒 microsecond resolution: 01:23:23.123123.  assumes Ltime.
        Llongfile                     // 绝对路径和行号 full file name and line number: /a/b/c/d.go:23
        Lshortfile                    // 文件和行号 final file name element and line number: d.go:23. overrides Llongfile
        LUTC                          // 转换时区 if Ldate or Ltime is set, use UTC rather than the local time zone
        LstdFlags     = Ldate | Ltime // 标准日志抬头信息 initial values for the standard logger
)

实例

# file: testlog.go

package main

import "log"

func init() {
    # 设置日志的前缀
    log.SetPrefix("TEST LOG ")
    # 设置日志抬头信息
    log.SetFlags(log.LstdFlags|Lshortfile)
}

func test(name string) {    
    log.Printf("Hello %s\n", name)
}

func main() {
    test("Golang")
    test("Python")
}

运行上面例子的代码会输出以下内容

TEST LOG 2018/03/25 22:00:53 log.go:14: Hello Golang
TEST LOG 2018/03/25 22:00:53 log.go:14: Hello Python

注：我们一般会把日志的初始化放在init函数中，golang在执行main函数之前会执行init函数

如何定制我们项目日志

实际开发过程中，我们都会把程序的日志记录在文件中，而不是直接在终端中输出，log包中的New函数可以创建一个新的记录器，定制我们的日志

// file: testlog_1.go

package main

import (
    "os"
    "log"
)


var logger *log.Logger
var f *os.File
var err error

func init() {
    f, err = os.OpenFile("test.log", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
    if err != nil {
        logger.Fatal(err)
    }
    logger = log.New(f, "", log.LstdFlags)
    logger.SetPrefix("TEST LOG ")
    logger.SetFlags(log.LstdFlags|log.Lshortfile)
}

func test(name string) {    
    logger.Printf("Hello %s", name)
}

func main(){
    test("Golang")
    test("Python")
    defer f.Close()
}

运行上面程序后，在当前目录下会生成test.log文件，且文件记录了我们写进去日志

$ cat test.log

TEST LOG 2018/03/25 22:37:02 log.go:26: Hello Golang
TEST LOG 2018/03/25 22:37:02 log.go:26: Hello Python

你是不是也觉得官方的日志处理包log没有进行很好的封装，用起来总有那么一点不顺手或者憋屈，没关系，github上有一个日志处理包go-logging，肯定是你的菜，看看官方的例子

package main

import (
    "os"

    "github.com/op/go-logging"
)

var log = logging.MustGetLogger("example")

// Example format string. Everything except the message has a custom color
// which is dependent on the log level. Many fields have a custom output
// formatting too, eg. the time returns the hour down to the milli second.
var format = logging.MustStringFormatter(
    `%{color}%{time:15:04:05.000} %{shortfunc} ▶ %{level:.4s} %{id:03x}%{color:reset} %{message}`,
)

// Password is just an example type implementing the Redactor interface. Any
// time this is logged, the Redacted() function will be called.
type Password string

func (p Password) Redacted() interface{} {
    return logging.Redact(string(p))
}

func main() {
    // For demo purposes, create two backend for os.Stderr.
    backend1 := logging.NewLogBackend(os.Stderr, "", 0)
    backend2 := logging.NewLogBackend(os.Stderr, "", 0)

    // For messages written to backend2 we want to add some additional
    // information to the output, including the used log level and the name of
    // the function.
    backend2Formatter := logging.NewBackendFormatter(backend2, format)

    // Only errors and more severe messages should be sent to backend1
    backend1Leveled := logging.AddModuleLevel(backend1)
    backend1Leveled.SetLevel(logging.ERROR, "")

    // Set the backends to be used.
    logging.SetBackend(backend1Leveled, backend2Formatter)

    log.Debugf("debug %s", Password("secret"))
    log.Info("info")
    log.Notice("notice")
    log.Warning("warning")
    log.Error("err")
    log.Critical("crit")
}

输出如下（还有颜色喔…）