go interface 转 string,解析json

package mainimport ("encoding/json""fmt")var user map[string]interface{}func main() {userJson := "{\"username\":\"system\",\"password\":\"123456\"}"json.Unmarshal([]byte(userJson), &user)fmt.Println(user) //打印结果:map[password:123456 username:system]username := user["username"]fmt.Println("username  ==", username) //username  == system//判断username的长度不为0,//if len(username) != 0 {//直接使用,报错invalid argument username (type interface {}) for lenif len(username.(string)) != 0 {//通过.(string)转换成string类型fmt.Println("输入合法")} else {fmt.Println("输入不合法")}}