参考
Package log implements a simple logging package. It defines a type, Logger, with methods for formatting output. It also has a predefined ‘standard’ Logger accessible through helper functions Print[f|ln], Fatal[f|ln], and Panic[f|ln], which are easier to use than creating a Logger manually. That logger writes to standard error and prints the date and time of each logged message. Every log message is output on a separate line: if the message being printed does not end in a newline, the logger will add one. The Fatal functions call os.Exit(1) after writing the log message. The Panic functions call panic after writing the log message.
log包是一个简单的日志，定义了type,Logger和一些输出格式。可以跟Print，Fatal，Panic一起使用，使用Fatal，Panic的时候会在打出日志信息后调用本身。可以很简单的手动创建一个Logger。每跳日志信息是单独的一行。
例子1
package main
import (
"bytes"
"fmt"
"log"
)
func main() {
var (
buf bytes.Buffer
logger = log.New(&buf, "logger: ", log.Lshortfile)
)
logger.Print("Hello, log file!")
fmt.Print(&buf)
}
输出结果为：
logger: prog.go:15: Hello, log file!
例子2
package main
import (
"bytes"
"fmt"
"log"
)
func main() {
var (
buf bytes.Buffer
logger = log.New(&buf, "INFO: ", log.Lshortfile)
infof = func(info string) {
logger.Output(2, info)
}
)
infof("Hello world")
fmt.Print(&buf)
}
输出结果为：
INFO: prog.go:19: Hello world
Program exited.
日志前缀
// These flags define which text to prefix to each log entry generated by the Logger.
const (
Ldate = 1 << iota // the date in the local time zone: 2009/01/23
Ltime // the time in the local time zone: 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
LUTC // if Ldate or Ltime is set, use UTC rather than the local time zone
Lmsgprefix // move the "prefix" from the beginning of the line to before the message
LstdFlags = Ldate | Ltime // initial values for the standard logger
)
Logger定义
type Logger struct {
mu sync.Mutex // ensures atomic writes; protects the following fields
prefix string // prefix on each line to identify the logger (but see Lmsgprefix)
flag int // properties
out io.Writer // destination for output
buf []byte // for accumulating text to write
}
主要的函数
New：创建一个Logger。
func New(out io.Writer, prefix string, flag int) *Logger {
return &Logger{out: out, prefix: prefix, flag: flag}
}
SetOutput：设置Logger的输出对象
func (l *Logger) SetOutput(w io.Writer) {
l.mu.Lock()
defer l.mu.Unlock()
l.out = w
}
Printf，Print，Println
func (l *Logger) Printf(format string, v ...interface{}) {
l.Output(2, fmt.Sprintf(format, v...))
}
// Print calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Print.
func (l *Logger) Print(v ...interface{}) { l.Output(2, fmt.Sprint(v...)) }
// Println calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Println.
func (l *Logger) Println(v ...interface{}) { l.Output(2, fmt.Sprintln(v...)) }
Fatal，Fatalf，Fatalln
// Fatal is equivalent to l.Print() followed by a call to os.Exit(1).
func (l *Logger) Fatal(v ...interface{}) {
l.Output(2, fmt.Sprint(v...))
os.Exit(1)
}
// Fatalf is equivalent to l.Printf() followed by a call to os.Exit(1).
func (l *Logger) Fatalf(format string, v ...interface{}) {
l.Output(2, fmt.Sprintf(format, v...))
os.Exit(1)
}
// 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)
}
Panic，Panicf,Panicln
func (l *Logger) Panic(v ...interface{}) {
s := fmt.Sprint(v...)
l.Output(2, s)
panic(s)
}
// Panicf is equivalent to l.Printf() followed by a call to panic().
func (l *Logger) Panicf(format string, v ...interface{}) {
s := fmt.Sprintf(format, v...)
l.Output(2, s)
panic(s)
}
// Panicln is equivalent to l.Println() followed by a call to panic().
func (l *Logger) Panicln(v ...interface{}) {
s := fmt.Sprintln(v...)
l.Output(2, s)
panic(s)
}
