database:
 host: 127.0.0.1
 user: root
 dbname: test
 pwd: 123456

package main 
import (
 "fmt"
 "os" 
 "github.com/spf13/viper"
)
 
func main() {
 //获取项目的执行路径
 path, err := os.Getwd()
 if err != nil {
 panic(err)
 }
 
 config := viper.New() 
 config.AddConfigPath(path)  //设置读取的文件路径
 config.SetConfigName("config") //设置读取的文件名
 config.SetConfigType("yaml") //设置文件的类型
 //尝试进行配置读取
 if err := config.ReadInConfig(); err != nil {
 panic(err)
 }
 
 //打印文件读取出来的内容:
 fmt.Println(config.Get("database.host"))
 fmt.Println(config.Get("database.user"))
 fmt.Println(config.Get("database.dbname"))
 fmt.Println(config.Get("database.pwd")) 
}

127.0.0.1
root
test
123456

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
 })