golang 反射使用加实战 ini配置文件解析

变量介绍

类型信息，这部分是元信息，是预先定义好的
值类型，这部分是程序运行过程中，动态改变的

变量介绍

反射介绍

反射与空接口

空接口可以存储任何类型的变量
那么给你一个空接口，怎么获取里面存储的内容
在运行时动态的获取一个变量的类型信息和值信息，就叫反射

怎么类型和详细信息

reflectreflectTypeOfreflect.ValueOf

基本数据类型分析

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var x float64 = 3.4
    reflectExample(x)
    reflectValue(x)
    reflectSetValue(&x)
    fmt.Printf("x value is %v\n", x)
    var b *int = new(int)
    *b = 100
    reflectSetValue(*b)
}

func reflectExample(a interface{}) {
    t := reflect.TypeOf(a)
    fmt.Printf("type of a is:%v\n", t)
    switch t.Kind() {
    case reflect.Int64:
        fmt.Printf("a is Int64\n")
    case reflect.Float64:
        fmt.Printf("a is Float64\n")
    case reflect.Ptr:
        fmt.Printf("a is Ptr\n")
    }
}

func reflectValue(a interface{}) {
    v := reflect.ValueOf(a)
    switch v.Kind() {
    case reflect.Int64:
        fmt.Printf("a is int64, store value is:%d\n", v.Int())
    case reflect.Float64:
        fmt.Printf("a is float64, store value is:%f\n", v.Float())
    }
}

func reflectSetValue(a interface{})  {
    v := reflect.ValueOf(a)
    switch v.Kind() {
    case reflect.Int64:
        v.SetInt(100)
        fmt.Printf("a is int64, store value is:%d\n", v.Int())
    case reflect.Float64:
        v.SetFloat(6.8)
        fmt.Printf("a is float64, store value is:%f\n", v.Float())
    case reflect.Ptr:
        fmt.Printf("set a to 6.8\n")
        v.Elem().SetFloat(6.8)
    default:
        fmt.Printf("default switch\n")
    }
}

Type.Kind()

func reflectExample(a interface{}) {
    t := reflect.TypeOf(a)
    fmt.Printf("type of a is:%v\n", t)
    switch t.Kind() {
    case reflect.Int64:
        fmt.Printf("a is Int64\n")
    case reflect.Float64:
        fmt.Printf("a is Float64\n")
    case reflect.Ptr:
        fmt.Printf("a is Ptr\n")
    }
}

Kind

// A Kind represents the specific kind of type that a Type represents.
// The zero Kind is not a valid kind.
type Kind uint

const (
    Invalid Kind = iota
    Bool
    Int
    Int8
    Int16
    Int32
    Int64
    Uint
    Uint8
    Uint16
    Uint32
    Uint64
    Uintptr
    Float32
    Float64
    Complex64
    Complex128
    Array
    Chan
    Func
    Interface
    Map
    Ptr
    Slice
    String
    Struct
    UnsafePointer
)

reflect.ValueOf

  var x float64 = 3.4
  v := reflect.ValueOf(x)
  
  // 和 reflect.TypeOf  功能是一样的
  fmt.Println("type:",v.Type())
  fmt.Println("kind is float64:",v.Kind() == reflect.Float64)
  fmt.Println("value:",v.Float())

通过反射设置变量的值

func reflectSetValue(a interface{})  {
    v := reflect.ValueOf(a)
    switch v.Kind() {
    case reflect.Int64:
        v.SetInt(100)
        fmt.Printf("a is int64, store value is:%d\n", v.Int())
    case reflect.Float64:
        v.SetFloat(6.8)
        fmt.Printf("a is float64, store value is:%f\n", v.Float())
    case reflect.Ptr:
        fmt.Printf("set a to 6.8\n")
        v.Elem().SetFloat(6.8)
    default:
        fmt.Printf("default switch\n")
    }
}

这里需要传递地址进去才能修改值，不传地址的话，改变的是拷贝变量的值，所以在 reflect 包会发生 panic

结构体反射

获取结构体相关信息

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string
    Sex   int
    Age   int
    Score float32
}

func main() {
    var s Student
    v := reflect.ValueOf(s)
    t := v.Type()

    switch t.Kind() {
    case reflect.Int64:
        fmt.Printf("s is int64\n")
    case reflect.Float32:
        fmt.Printf("s is int64\n")
    case reflect.Struct:
        fmt.Printf("s is struct\n")
        fmt.Printf("field num of s is %d\n", v.NumField())
        for i := 0; i < v.NumField(); i++ {
            field := v.Field(i)
            fmt.Printf("name:%s type:%v value:%v\n",
                t.Field(i).Name, field.Type().Kind(), field.Interface())
        }
    default:
        fmt.Printf("default\n")
    }
}

设置结构体相关字段的值

package main

import (
    "reflect"

    "fmt"
)

type Student struct {
    Name  string
    Sex   int
    Age   int
    Score float32
}

func main() {
    var s Student
    v := reflect.ValueOf(&s)
    v.Elem().Field(0).SetString("张高元")
    v.Elem().FieldByName("Sex").SetInt(1)
    v.Elem().FieldByName("Age").SetInt(18)
    v.Elem().FieldByName("Score").SetFloat(99.2)

    fmt.Printf("s：%#v\n", s)
}

获取结构体的方法信息

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string
    Sex   int
    Age   int
    Score float32
}

func (s *Student) SetName(name string) {
    s.Name = name
}

func (s *Student) Print() {
    fmt.Printf("通过反射进行调用:%#v\n", s)
}

func main() {
    var s Student
    s.SetName("xxxx")
    v := reflect.ValueOf(&s)
    t := v.Type()
    fmt.Printf("struct student have %d methods\n", t.NumMethod())
    for i := 0; i < t.NumMethod(); i++ {
        method := t.Method(i)
        fmt.Printf("struct %d method, name:%s type:%v\n", i, method.Name, method.Type)
    }
}

调用结构体中的方法

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string
    Sex   int
    Age   int
    Score float32
}

func (s *Student) SetName(name string) {
    s.Name = name
}

func (s *Student) Print() {
    fmt.Printf("通过反射进行调用:%#v\n", s)
}

func main() {
    var s Student
    s.SetName("xxxx")
    v := reflect.ValueOf(&s)
    t := v.Type()
    fmt.Printf("struct student have %d methods\n", t.NumMethod())
    for i := 0; i < t.NumMethod(); i++ {
        method := t.Method(i)
        fmt.Printf("struct %d method, name:%s type:%v\n", i, method.Name, method.Type)
    }

    //通过reflect.Value获取对应的方法并调用
    m1 := v.MethodByName("Print")
    var args []reflect.Value
    m1.Call(args)

    m2 := v.MethodByName("SetName")
    var args2 []reflect.Value
    name := "stu01"
    nameVal := reflect.ValueOf(name)
    args2 = append(args2, nameVal)
    m2.Call(args2)
    m1.Call(args)
}

tag

package main

import (
    "fmt"
    "reflect"
)

type Student struct {
    Name  string `json:"name" db:"name"`
    Sex   int
    Age   int
    Score float32
}

func (s *Student) SetName(name string) {
    s.Name = name
}

func (s *Student) Print() {
    fmt.Printf("通过反射进行调用:%#v\n", s)
}

func main() {
    var s Student
    s.SetName("xxx")
    v := reflect.ValueOf(&s)
    t := v.Type()
    field0 := t.Elem().Field(0)
    fmt.Printf("tag json=%s\n", field0.Tag.Get("json"))
    fmt.Printf("tag db=%s\n", field0.Tag.Get("db"))
}

反射总结以及应用场景

在运行时动态的获取一个变量的类型信息和值信息

应用场景

序列化和反序列化，比如 json、protobuf 等各种数据协议
各种数据库的 ORM，比如 gorm、sqlx 等数据库中间件
配置文件解析相关的库，比如yaml、ini

以上所有场景我们都不知道具体的类型，所以要用反射