Use of go log package log

1、log brief introduction
golang Built in log package , Implement a simple log service . By calling log Function of the package , Simple log printing function can be realized .

2、log Use
log There is... In the bag 3 A series of log printing functions , , respectively, print series 、panic series 、fatal series .

Function series effect
print Print log only
panic Print log , Throw out panic abnormal
fatal Print log , Force end procedure (os.Exit(1)),defer Function does not execute
2.1 A simple example
func main() {
defer fmt.Println(“panic Processing before exiting ”)
log.Println(“println journal ”)
log.Panic(“panic journal ”)
log.Fatal(“ Program exit log ”)
}
Result example （ The actual result is not like this , because panic,fatal Will affect the execution of the program ）：

2020/06/02 11:04:17 println journal
2020/06/02 11:04:17 panic journal
2020/06/02 11:04:17 panic Processing before exiting
2020/06/02 11:04:17 Program exit log
3、log To configure
3.1 standard log To configure
By default log Only the time will be printed , But in practice, we may also need to get the file name , Line number and other information ,log The package provides us with customized interfaces .
log The package provides two standards log Configuration related methods ：

func Flags() int // Return to standard log Output configuration
func SetFlags(flag int) // Set standards log Output configuration
flag Parameters
const (
// Control details of output log information , Unable to control the order and format of the output .
// Output logs are separated by a colon after each entry ： for example 2009/01/23 01:23:23.123123 /a/b/c/d.go:23: message
Ldate = 1 << iota // date ：2009/01/23
Ltime // Time ：01:23:23
Lmicroseconds // Microsecond level time ：01:23:23.123123（ For enhancement Ltime position ）
Llongfile // File full pathname + Line number ： /a/b/c/d.go:23
Lshortfile // file name + Line number ：d.go:23（ Will overwrite Llongfile）
LUTC // Use UTC Time
LstdFlags = Ldate | Ltime // standard logger The initial value of the
)
Example of standard log configuration
func init() {
log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)

}
func main() {
log.Println(“println journal ”)
}
Output results ：

image.png
3.2 Log prefix configuration
log Package provides two related functions for log prefix configuration ：

func Prefix() string // Returns the prefix configuration of the log
func SetPrefix(prefix string) // Set the log prefix
Log prefix configuration instance
func init() {
log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)
log.SetPrefix(“success”)
}
func main() {
log.Println(“println journal ”)
}
Output results ：

image.png
3.3 Log output location configuration
The previous introduction is to output logs to the console ,golang Of log The package also supports exporting logs to a file .log The package provided. func SetOutput(w io.Writer) function , Output the log to a file .

Log output location configuration
func init() {
log.SetFlags(log.Ldate | log.Ltime | log.Lshortfile)
logFile, err := os.OpenFile(“./c.log”, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
if err != nil {
log.Panic(“ Opening the log file is abnormal ”)
}
log.SetOutput(logFile)
}
func main() {
log.Println(“println journal ”)
}
result ： Log output to the current directory c.log In file

image.png
4、 Customize logger
log Package provides us with built-in functions , Let us customize logger. In terms of effect , Is to put the title 3 Standard log configuration in 、 Log prefix configuration 、 The log output location configuration is integrated into one function , Make the log configuration less cumbersome .
log The package provides func New(out io.Writer, prefix string, flag int) *Logger Function to implement custom logger.

Example
var logger *log.Logger

func init() {
logFile, err := os.OpenFile(“./c.log”, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
if err != nil {
log.Panic(“ Opening the log file is abnormal ”)
}
logger = log.New(logFile, “success”, log.Ldate | log.Ltime | log.Lshortfile)
}
func main() {
logger.Println(“ Customize logger”)
}