go interface 轉 string,解析json

package main

import (
	"encoding/json"
	"fmt"
)

var user map[string]interface{}

func main() {
	userJson := "{\"username\":\"system\",\"password\":\"123456\"}"
	json.Unmarshal([]byte(userJson), &user)
	fmt.Println(user) //打印結果:map[password:123456 username:system]
	username := user["username"]
	fmt.Println("username  ==", username) //username  == system
	//判斷username的長度不爲0,
	//if len(username) != 0 {//直接使用,報錯invalid argument username (type interface {}) for len
	if len(username.(string)) != 0 {//通過.(string)轉換成string類型
		fmt.Println("輸入合法")
	} else {
		fmt.Println("輸入不合法")
	}
}