viperInstance := viper.New()	// viper实例
viperInstance.WatchConfig()
viperInstance.OnConfigChange(func(e fsnotify.Event) {
	log.Print("Config file updated.")
	viperLoadConf(viperInstance)  // 加载配置的方法
})

func (v *Viper) WatchConfig() {
	go func() {
      // 建立新的监视处理程序，开启一个协程开始等待事件
      // 从I/O完成端口读取，将事件注入到Event对象中：Watcher.Events
		watcher, err := fsnotify.NewWatcher()  
		if err != nil {
			log.Fatal(err)
		}
		defer watcher.Close()
 
		// we have to watch the entire directory to pick up renames/atomic saves in a cross-platform way
		filename, err := v.getConfigFile()  
		if err != nil {
			log.Println("error:", err)
			return
		}
 
		configFile := filepath.Clean(filename)    //配置文件E:\etc\bizsvc\config.yml
		configDir, _ := filepath.Split(configFile)  // E:\etc\bizsvc 
		done := make(chan bool)
		go func() {
			for {
				select {
        // 读取的event对象有两个属性，Name为E:\etc\bizsvc\config.yml，Op为write（对文件的操作）
				case event := <-watcher.Events:
		// 清除内部的..和他前面的元素，清除当前路径.，用来判断操作的文件是否是configFile
					if filepath.Clean(event.Name) == configFile {
        // 如果对该文件进行了创建操作或写操作
						if event.Op&fsnotify.Write == fsnotify.Write || event.Op&fsnotify.Create == fsnotify.Create {
							err := v.ReadInConfig()
							if err != nil {
								log.Println("error:", err)
							}
							v.onConfigChange(event)
						}
					}
				case err := <-watcher.Errors:
         // 有错误将打印
					log.Println("error:", err)
				}
			}
		}()
 
		watcher.Add(configDir)
		<-done
	}()
}

type Viper struct {
	// Delimiter that separates a list of keys
	// used to access a nested value in one go
	keyDelim string
 
	// A set of paths to look for the config file in
	configPaths []string
 
	// The filesystem to read config from.
	fs afero.Fs
 
	// A set of remote providers to search for the configuration
	remoteProviders []*defaultRemoteProvider
 
	// Name of file to look for inside the path
	configName string
	configFile string
	configType string
	envPrefix string
 
	automaticEnvApplied bool
	envKeyReplacer   *strings.Replacer
 
	config     map[string]interface{}
	override    map[string]interface{}
	defaults    map[string]interface{}
	kvstore    map[string]interface{}
	pflags     map[string]FlagValue
	env      map[string]string
	aliases    map[string]string
	typeByDefValue bool
 
	// Store read properties on the object so that we can write back in order with comments.
	// This will only be used if the configuration read is a properties file.
	properties *properties.Properties
 
	onConfigChange func(fsnotify.Event)
}

func (v *Viper) OnConfigChange(run func(in fsnotify.Event)) {
	v.onConfigChange = run
}

	viperInstance.OnConfigChange(func(e fsnotify.Event) {
		log.Print("Config file updated.")
		viperLoadConf(viperInstance)  // viperLoadConf函数就是将最新配置注入到自定义结构体对象的逻辑
	})