golang基础-反射获取（基础数据、结构体）、操作（基本类型、结构体、指针）、反射获取Tag

反射获取基本类型

反射：可以在运行时动态获取变量的相关信息

Import (“reflect”)

a. reflect.TypeOf，获取变量的类型，返回reflect.Type类型

b. reflect.ValueOf，获取变量的值，返回reflect.Value类型

c. reflect.Value.Kind，获取变量的类别，返回一个常量

d. reflect.Value.Interface()，转换成interface{}类型

var x float64 = 3.4
fmt.Println("type:", reflect.TypeOf(x))
v := reflect.ValueOf(x)
fmt.Println("value:", v)
fmt.Println("type:", v.Type())
fmt.Println("kind:", v.Kind())
fmt.Println("value:", v.Float())

fmt.Println(v.Interface())
fmt.Printf("value is %5.2e\n", v.Interface())
y := v.Interface().(float64)
fmt.Println(y)

输出如下：

type: float64
value: 3.4
type: float64
kind: float64
value: 3.4
3.4
value is 3.40e+00
3.4

反射获取结构体

package main

import (
"fmt"
"reflect"
)

type Student struct {
Name  string
Age   int
Score float32
}

func test(b interface{}) {
t := reflect.TypeOf(b)
fmt.Println(t)

v := reflect.ValueOf(b)
fmt.Println(v)

k := v.Kind()
fmt.Println(k)

iv := v.Interface()
fmt.Println(iv)

stu, ok := iv.(Student)
if ok {
fmt.Printf("%v %T\n", stu, stu)
}
}

func main() {
var a Student = Student{
Name:  "stu01",
Age:   18,
Score: 92,
}
test(a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
main.Student
{stu01 18 92}
struct
{stu01 18 92}
{stu01 18 92} main.Student
PS E:\golang\go_pro\src\safly>

Elem反射操作基本类型

用来获取指针指向的变量，相当于：

var a *int;

func main() {

var b int = 1
b = 200
testInt(&b)
fmt.Println(b)
}

//fv.Elem()用来获取指针指向的变量
func testInt(b interface{}) {
val := reflect.ValueOf(b)
val.Elem().SetInt(100)
c := val.Elem().Int()

fmt.Printf("get value  interface{} %d\n", c)
fmt.Printf("string val:%d\n", val.Elem().Int())
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
get value  interface{} 100
string val:100
100
PS E:\golang\go_pro\src\safly>

反射调用结构体方法

package main

import (
"fmt"
"reflect"
)

type Student struct {
Name  string
Age   int
Score float32

}

func (s Student) Print(){
fmt.Println(s)
}

func (s Student) Set(name string,age int,score float32){
s.Age = age
s.Name = name
s.Score = score
}

func TestStruct(a interface{}) {
val := reflect.ValueOf(a)
kd := val.Kind()

fmt.Println(val,kd)
if kd != reflect.Struct {
fmt.Println("expect struct")
return
}
//获取字段数量
fields:= val.NumField()
fmt.Printf("struct has %d field\n",fields)
//获取字段的类型
for i:=0;i<fields;i++{
fmt.Printf("%d %v\n",i,val.Field(i).Kind())
}
//获取方法数量
methods:=val.NumMethod()
fmt.Printf("struct has %d methods\n",methods)

//反射调用的Print方法
var params []reflect.Value
val.Method(0).Call(params)

}

func main() {
var a Student = Student{
Name:  "stu01",
Age:   18,
Score: 92.8,
}
TestStruct(a)
// fmt.Println(a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
{stu01 18 92.8} struct
struct has 3 field
0 string
1 int
2 float32
struct has 2 methods
{stu01 18 92.8}
PS E:\golang\go_pro\src\safly>

Elem反射操作结构体

package main

import (
"fmt"
"reflect"
)

type Student struct {
Name  string
Age   int
Score float32

}

func (s Student) Print(){
fmt.Println(s)
}

func (s Student) Set(name string,age int,score float32){
s.Age = age
s.Name = name
s.Score = score
}

func TestStruct(a interface{}) {
val := reflect.ValueOf(a)
kd := val.Kind()

fmt.Println(val,kd)
if kd!= reflect.Ptr && val.Elem().Kind() ==  reflect.Struct {
fmt.Println("expect struct")
return
}
//获取字段数量
fields:= val.Elem().NumField()
fmt.Printf("struct has %d field\n",fields)
//获取字段的类型
for i:=0;i<fields;i++{
fmt.Printf("%d %v\n",i,val.Elem().Field(i).Kind())
}
//获取方法数量
methods:=val.NumMethod()
fmt.Printf("struct has %d methods\n",methods)

//反射调用的Print方法
var params []reflect.Value
val.Elem().Method(0).Call(params)
}

func main() {
var a Student = Student{
Name:  "stu01",
Age:   18,
Score: 92.8,
}
TestStruct(&a)
// fmt.Println(a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
&{stu01 18 92.8} ptr
struct has 3 field
0 string
1 int
2 float32
struct has 2 methods
{stu01 18 92.8}
PS E:\golang\go_pro\src\safly>

Elem反射获取tag

package main

import (
"fmt"
"reflect"
)

type Student struct {
Name  string `json:"stu_name"`
Age   int
Score float32

}

func (s Student) Print(){
fmt.Println(s)
}

func (s Student) Set(name string,age int,score float32){
s.Age = age
s.Name = name
s.Score = score
}

func TestStruct(a interface{}) {
typ := reflect.TypeOf(a)

tag := typ.Elem().Field(0).Tag.Get("json")
fmt.Printf("Tag:%s\n",tag)
}

func main() {
var a Student = Student{
Name:  "stu01",
Age:   18,
Score: 92.8,
}
TestStruct(&a)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
Tag:stu_name
PS E:\golang\go_pro\src\safly>

练习例子

package main

import (
"fmt"
"reflect"
)

type T struct {
A int
B string
}

func main() {
t := T{23, "skidoo"}
s := reflect.ValueOf(&t).Elem()
typeOfT := s.Type()
for i := 0; i < s.NumField(); i++ {
f := s.Field(i)
fmt.Printf("%d: %s %s = %v\n", i,
typeOfT.Field(i).Name, f.Type(), f.Interface())
}
s.Field(0).SetInt(77)
s.Field(1).SetString("Sunset Strip")
fmt.Println("t is now", t)
}

输出如下：

PS E:\golang\go_pro\src\safly> go run demo.go
0: A int = 23
1: B string = skidoo
t is now {77 Sunset Strip}
PS E:\golang\go_pro\src\safly>