golang利用反射获取或设置环境变量

envvar.go

package envvar

import (
	"encoding/json"
	"fmt"
	"os"
	"reflect"
	"strconv"
	"strings"
)

// MustUnmarshalFromEnvs Get value form Enviroment
// v must be ptr
//   ref: https://www.zhihu.com/question/22783511/answer/24960616
//   ref: https://blog.csdn.net/skh2015java/article/details/79292743
func MustUnmarshalFromEnvs(v interface{}, prefix string) {

	m := make(map[string]interface{})

	// rv := reflect.Indirect(reflect.ValueOf(v))
	rv := reflect.ValueOf(v)

	if rv.Kind() != reflect.Ptr {
		err := fmt.Errorf("want a Struct Ptr , Got a %v", rv.Kind())
		panic(err)
	}

	rvIndirect := reflect.Indirect(rv)
	if rvIndirect.Kind() != reflect.Struct {
		err := fmt.Errorf("want a Struct Ptr, got a %v", rvIndirect.Kind())
		panic(err)
	}

	typ := rvIndirect.Type()
	for i := 0; i < typ.NumField(); i++ {
		filed := typ.Field(i)
		// spew.Dump(filed)

		tag := filed.Tag.Get("env")

		envName := fmt.Sprintf("%s_%s", prefix, strings.ToUpper(TagHead(tag)))
		envValue := os.Getenv(envName)

		switch filed.Type.Kind() {
		case reflect.String:
			m[filed.Name] = envValue

		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
			m[filed.Name] = ParseNumber(envValue)

		case reflect.Bool:
			m[filed.Name] = ParseBool(envValue)
		}

	}

	bBytes, _ := json.Marshal(m)

	err := json.Unmarshal(bBytes, v)
	if err != nil {
		panic(err)
	}

}

func TagHead(tag string) string {
	l := strings.Split(tag, ",")
	return l[0]
}

func ParseBool(s string) bool {
	switch strings.ToLower(s) {
	case "t", "true":
		return true
	case "f", "false":
		return false
	default:
		return false
	}
}

func ParseNumber(s string) int64 {
	n, err := strconv.ParseInt(s, 10, 64)
	if err != nil {
		// panic(err)
		return 0
	}
	return n
}

envvar_test.go

package envvar

import (
	"os"
	"testing"

	"github.com/davecgh/go-spew/spew"
	. "github.com/smartystreets/goconvey/convey"
)

type Person struct {
	Name   string `env:"name,omitempty"`
	Age    int    `env:"age,omitempty"`
	Gender bool   `env:"gender,omitempty"`
}

func Test_MustUnmarshalFromEnv(t *testing.T) {

	var p = Person{}
	os.Setenv("CI_PROJECT_NAME", "zhangsanfeng")
	os.Setenv("CI_PROJECT_AGE", "12")
	os.Setenv("CI_PROJECT_GENDER", "false")

	MustUnmarshalFromEnvs(&p, "CI_PROJECT")

	spew.Dump(p)

	Convey("判断环境变量读取结果", t, func() {
		So(p.Name, ShouldEqual, "zhangsanfeng")
		So(p.Age, ShouldEqual, 12)
		So(p.Gender, ShouldBeFalse)
	})
}