go的struct的tag反射

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package main

import (
	"encoding/json"
	"fmt"
	"reflect" // 这里引入reflect模块
)

func testTag1(){
	type A struct {
		B string `tag1:"b" tag2:"B" tag3:"d"` //这引号里面的就是tag
		C string `tag1:"c" tag2:"C"`
	}
	user := &A{"fmt", "reflect"}
	fmt.Printf("这是>>user=%v\n",user)
	s := reflect.TypeOf(user).Elem() //通过反射获取type定义
	fmt.Printf("这是>>s=%v 长度:%d\n",s,s.NumField())
	for i := 0; i < s.NumField(); i++ {
		fmt.Println("将tag输出出来>>",s.Field(i).Tag) //将tag输出出来
		fmt.Println("tag2>>",s.Field(i).Tag.Get("tag2")) //将tag输出出来
		fmt.Println("tag3>>",s.Field(i).Tag.Get("tag3")) //将tag输出出来
	}
}

func testTag2(){
	type S struct {
		F string `species:"gopher" color:"blue"`
	}
	s1 := S{}
	st := reflect.TypeOf(s1)
	field := st.Field(0)
	fmt.Println(field.Tag.Get("color"), field.Tag.Get("species"))
}


func testTag3(){
	type User struct {
		UserId   int    `json:"user_id" bson:"user_id"`
		UserName string `json:"user_name" bson:"user_name"`
	}
	// 输出json格式
	u := &User{UserId: 1, UserName: "tony"}
	j, _ := json.Marshal(u)
	fmt.Println(string(j))
	// 输出内容：{"user_id":1,"user_name":"tony"}

	// 获取tag中的内容
	t := reflect.TypeOf(u)
	field := t.Elem().Field(0)
	fmt.Println(field.Tag.Get("json"))
	// 输出：user_id
	fmt.Println(field.Tag.Get("bson"))
	// 输出：user_id
}

func main() {
	//testTag1()
	//testTag2()
	testTag3()
}

testTag3()输出:

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{"user_id":1,"user_name":"tony"}
user_id
user_id

testTag1()和testTag2()输出:

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这是>>user=&{fmt reflect}
这是>>s=main.A 长度:2
将tag输出出来>> tag1:"b" tag2:"B" tag3:"d"
tag2>> B
tag3>> d
将tag输出出来>> tag1:"c" tag2:"C"
tag2>> C
tag3>>
blue gopher