golang log 包

一、快速使用
Golang的log包短小精悍,可以非常轻松的实现日志打印转存功能。不用多说,log支持并发操作(即协程安全-相对于JAVA中的线程安全而言),其结构定义如下:

type Logger struct {
	mu sync.Mutex // ensures atomic writes; protects the following fields
	prefix string // prefix to write at beginning of each line // 日志行前缀
	flag int // properties // 日志打印格式标志,用于指定每行日志的打印格式
	out io.Writer // destination for output // 用于指定日志输出位置,理论上可以是任务地方,只要实现了io.Writer接口就行
	buf []byte // for accumulating text to write // 日志内容
}

log包定义了一些日志格式标志:

// These flags define which text to prefix to each log entry generated by the Logger.
const (
	// Bits or'ed together to control what's printed. There is no control over the
	// order they appear (the order listed here) or the format they present (as
	// described in the comments). A colon appears after these items:
	//	2009年01月23日 01:23:23.123123 /a/b/c/d.go:23: message
	Ldate = 1 << iota // the date: 2009年01月23日
	Ltime // the time: 01:23:23
	Lmicroseconds // microsecond resolution: 01:23:23.123123. assumes Ltime.
	Llongfile // full file name and line number: /a/b/c/d.go:23
	Lshortfile // final file name element and line number: d.go:23. overrides Llongfile
	LstdFlags = Ldate | Ltime // initial values for the standard logger
)

上述这些标志可以在创建Logger对象时指定(通过下面的New函数创建),也可以通过Logger.setFlat()方法动态指定。

Logger对象通过函数New创建

// New creates a new Logger. The out variable sets the
// destination to which log data will be written.
// The prefix appears at the beginning of each generated log line.
// The flag argument defines the logging properties.
func New(out io.Writer, prefix string, flag int) *Logger {
	return &Logger{out: out, prefix: prefix, flag: flag}
}

log包已默认提供了一个日志对象,并封装了包级别的常用函数,该对象将日志信息输出到标准输出设备中(开箱即用)。

var std = New(os.Stderr, "", LstdFlags) // 日志中只使用的flag为LstdFlags,即只输出日期

如果只是想输出到终端而不保存到文件等其它地方时,可以直接通过log.Xxxx()方式直接调用,因为这些包级别的函数只是对std对象相关方法的简单封装,如println函数定义如下:

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

二、Logger对象方法使用说明
Logger对象提供了如下几个方法:

func (l *Logger) Output(calldepth int, s string) error ; // 真正负责日志打印的方法,其它级别的打印方法都将会调用它
// Println calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Println.
func (l *Logger) Println(v ...interface{}) { // 一般信息打印方法,相当于JAVA中log的info级别
 l.Output(2, fmt.Sprintln(v...)) 
}
// Panicln is equivalent to l.Println() followed by a call to panic(). 
func (l *Logger) Panicln(v ...interface{}) { // 业务异常时使用的方法,该方法会抛出异常,调用方可以用recover捕获,相当于JAVA的ERROR级别(JAVA不会自动抛异常)
	s := fmt.Sprintln(v...)
	l.Output(2, s)
	panic(s) // 通过panic抛出异常,只有上层业务没捕获异常时,程序才会异常中止并退出,
}
// Fatalln is equivalent to l.Println() followed by a call to os.Exit(1).
func (l *Logger) Fatalln(v ...interface{}) { 
	l.Output(2, fmt.Sprintln(v...))
	os.Exit(1) // 调用该方法会中止应用程序并直接退出
}

使用例子1

package main
import (
 "log"
 "os"
 "io/ioutil"
 "io"
)
var (
 Trace *log.Logger // 记录所有日志
 Info *log.Logger // 重要的信息
 Warning *log.Logger // 需要注意的信息
 Error *log.Logger // 致命错误
)
func init() {
 file, err := os.OpenFile("file", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
 if err != nil {
 log.Fatalln("Failed to open error log file:", err)
 }
 Trace = log.New(ioutil.Discard, "TRACE: ", log.Ltime|log.Lshortfile)
 Info = log.New(os.Stdout, "Info: ", log.Ltime|log.Lshortfile)
 Warning = log.New(os.Stdout, "Warning: ", log.Ltime|log.Lshortfile)
 Error = log.New(io.MultiWriter(file, os.Stderr), "Error", log.Ltime|log.Lshortfile)
}
func main() {
 Trace.Println("I have something standard to say")
 Info.Println("Special Information")
 Warning.Println("There is something you need to know about")
 Error.Println("Something has failed")
}

使用例子2

package main
import (
 "bytes"
 "fmt"
	"log"
	"io"
	"io/ioutil"
	"os"
)
type Logger struct {
	// contains filtered or unexported fields
}	
var (
	Trace *log.Logger
	Info *log.Logger
	Warning *log.Logger
	Error *log.Logger
)
func Init( traceHandle io.Writer, infoHandle io.Writer, 
	warningHandle io.Writer, errorHandle io.Writer)(Trace,Info,Warning,Error *log.Logger) {
 Trace = log.New(traceHandle,"TRACE: ", log.Ldate|log.Ltime|log.Lshortfile)
 Info = log.New(infoHandle, "INFO: ", log.Ldate|log.Ltime|log.Lshortfile)
 Warning = log.New(warningHandle, "WARNING: ", log.Ldate|log.Ltime|log.Lshortfile)
	Error = log.New(errorHandle, "ERROR: ", log.Ldate|log.Ltime|log.Lshortfile)
	// Trace.Println("XXXXXXXXXXXX")
	return //Trace,Info,Warning,Error
}
func test_log2(){
	Trace,Info,Warning,Error :=Init(ioutil.Discard, os.Stdout, os.Stdout, os.Stderr)
	Trace.Println("I have something standard to say")
	Info.Println("Special Information")
	Warning.Println("There is something you need to know about")
	Error.Println("Something has failed")
}
func test_log1(){
	var buf bytes.Buffer
	logger := log.New(&buf, "logger: ", log.Lshortfile|log.Ldate)
 logger.Print("Hello, log file!")
 fmt.Print(&buf)
}
func main() {
	
	test_log1()
	test_log2()
	
}

更多参考

https://blog.csdn.net/cza55007/article/details/46039279

http://xiaorui.cc/2016/03/15/%E4%BD%BF%E7%94%A8golang-log%E5%BA%93%E5%8C%85%E5%AE%9E%E7%8E%B0%E6%97%A5%E5%BF%97%E6%96%87%E4%BB%B6%E8%BE%93%E5%87%BA/

https://studygolang.com/articles/3326

本文来自:开源中国博客

感谢作者:易野

查看原文:golang log 包

• 编辑
• 预览