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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: // 2009/01/23 01:23:23.123123 /a/b/c/d.go:23: message Ldate = 1 << iota // the date: 2009/01/23 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 }
三、使用示例
package test import ( "fmt" "log" "os" "testing" ) func TestLog(t *testing.T) { fmt.Println("begin TestLog ...") file, err := os.Create("test.log") if err != nil { log.Fatalln("fail to create test.log file!") } logger := log.New(file, "", log.LstdFlags|log.Llongfile) log.Println("1.Println log with log.LstdFlags ...") logger.Println("1.Println log with log.LstdFlags ...") logger.SetFlags(log.LstdFlags) log.Println("2.Println log without log.LstdFlags ...") logger.Println("2.Println log without log.LstdFlags ...") //log.Panicln("3.std Panicln log without log.LstdFlags ...") //fmt.Println("3 Will this statement be execute ?") //logger.Panicln("3.Panicln log without log.LstdFlags ...") log.Println("4.Println log without log.LstdFlags ...") logger.Println("4.Println log without log.LstdFlags ...") log.Fatal("5.std Fatal log without log.LstdFlags ...") fmt.Println("5 Will this statement be execute ?") logger.Fatal("5.Fatal log without log.LstdFlags ...") }
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