利用接口实现一个可扩展的日志系统：
1、日志对外接口：
本例中定义一个日志写入的接口(LogerWriter),要求写入设备必须遵守这个接口协议(实现这个接口)才能被日志器(Logger)注册。日志器有ResgisterWriter()和Log()两个方法，ResgisterWriter()方法将日志写入器(LogWriter)注册到日志器中，log()方法进行日志的输出，这个函数会将日志写入到所有已经注册的日志写入器(LogWriter)中。本例中简单实现文件和输出到终端这两种方式。
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package main
type LogWriter interface {
Write(data interface{}) error
}
type Logger struct {
writeList []LogWriter
}
func (l *Logger) RegisterWriter(writer LogWriter) {
l.writeList = append(l.writeList, writer)
}
func (l *Logger) Log(data interface{}) {
for _, writer := range l.writeList {
writer.Write(data)
}
}
func NewLogger() *Logger {
return &Logger{}
}
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2、文件写入器：
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package main
import (
"errors"
"fmt"
"os"
)
type fileWriter struct {
file *os.File
}
func (f *fileWriter) SetFile(filename string) (err error) {
if f.file != nil {
f.file.Close()
}
f.file, err = os.Create(filename)
return err
}
func (f *fileWriter) Write(data interface{}) error {
if f.file == nil {
return errors.New("file not created")
}
str := fmt.Sprintf("%v\n", data)
_, err := f.file.Write([]byte(str))
return err
}
func newFileWriter() *fileWriter {
return &fileWriter{}
}
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3、命令行写入器：
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package main
import (
"fmt"
"os"
)
type consoleWriter struct {
}
func (f *consoleWriter) Write(data interface{}) error {
str := fmt.Sprintf("%v\n", data)
_, err := os.Stdout.Write([]byte(str))
return err
}
func newConsolerWriter() *consoleWriter {
return &consoleWriter{}
}
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4、main.go
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package main
import "fmt"
func createLogger() *Logger {
l := NewLogger()
cw := newConsolerWriter()
l.RegisterWriter(cw)
fw := newFileWriter()
if err := fw.SetFile("log.log"); err != nil {
fmt.Println(err)
}
l.RegisterWriter(fw)
return l
}
func main() {
l := createLogger()
l.Log("hello")
}
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