解组入接口{}然后执行类型断言 [英] Unmarshaling Into an Interface{} and Then Performing Type Assertion
问题描述
我通过一个rabbitmq消息系统得到了一个 我转换和发送的结构可以是:(更改结构的名称和大小,但它应该没关系) 或 该消息完美地作为 直到现在一切正常。 第一次尝试是: 这不起作用。在Unmarshaling 甚至比这更陌生,map key是我得到的字符串,map值是空的。字符串
。在发送之前,我使用 json.Marshal
,将结果转换为 string code>并通过
发送rabbitmq。
type Somthing1 struct {
Thing string`json:thing`
OtherThing int64`json:other_thing`
}
type Somthing2 struct {
Croc int`json:croc`
Odile bool`json:odile`
$ b 字符串
并在另一面打印
(某些服务器)
现在我试图将它们转换回它们的结构并声明类型。
func typeAssert(msg string) {
var input interface {}
json.Unmarshal([] byte(msg),& input)
开关输入。 ){
case Somthing1:
job:= Somthing1 {}
job = input。(Somthing1)
queueResults(job)
case Somthing2:
stats:= Somthing2 {}
stats = input。(Somthing2)
queueStatsRes(stats)
default:
}
之后打印 input
类型时,我得到 map [string] interface {}
(? !)
$ p
$ b
func typeAssert(msg string){
var input interface {}
json.Unmarshal([] byte(msg),& input)
switch v:= input。(type){
(Somthing1)
queueResults(v)
case Somthing2:
v = input。(Somthing2)
queueStatsRes(v)
default:
}
这个答案:
Golang:无法在非界面值上键入开关
switch v:= interface {}(input)。(type)
仍然没有成功......
有什么想法? json
打包Unmarshals的默认类型显示在 Unmarshal
函数文档
bool,用于JSON布尔值
float64,用于JSON数字
字符串,用于JSON字符串
[] interface {},用于JSON数组
map [string]接口{},对于JSON对象
无JSON null
由于您解组为接口{}
,返回的类型将仅来自该集合。 json
包不知道 Something1
和 Something2
。您需要从json对象正在解组到的<
如果您不想从通用接口解包数据,或者以某种方式标记数据以便知道期望的类型,则可以迭代地使用json并尝试解组它到你想要的每种类型。
你甚至可以将它们打包到一个包装结构中,以便为你解组:
type Something1 struct {
Thing string`json:thing`
OtherThing int64`json:other_thing`
}
type Something2 struct {
Croc int`json:croc`
Odile bool`json:odile`
}
type Unpacker struct {
Data interface {}
}
func(u * Unpacker)UnmarshalJSON(b [] byte)错误{
smth1:=& Something1 {
err:= json.Unmarshal(b,smth1)
//没有错误,bu我们还需要确保我们解组了一些
,如果err == nil&& smth1.Thing!={
u.Data = smth1
返回零
}
//如果我们有错误类型以外的错误,则中止
if _,ok:= err。(* json.UnmarshalTypeError); err!= nil&& !ok {
return err
}
smth2:=& Something2 {}
err = json.Unmarshal(b,smth2)
if err != nil {
return err
}
u.Data = smth2
return nil
}
http://play.golang .org / p / Trwd6IShDW
I get a string
through a rabbitmq message system. Before sending,
I use json.Marshal
, convert the outcome to string
and send through
rabbitmq.
The structs that I convert and send can be: (changed the names and the size of the structs but it should not matter)
type Somthing1 struct{
Thing string `json:"thing"`
OtherThing int64 `json:"other_thing"`
}
or
type Somthing2 struct{
Croc int `json:"croc"`
Odile bool `json:"odile"`
}
The message goes through perfectly as a string
and is printed
on the other side (some server)
Up until now everything works. Now I'm trying to convert them back into their structs and assert the types.
first attempt is by:
func typeAssert(msg string) {
var input interface{}
json.Unmarshal([]byte(msg), &input)
switch input.(type){
case Somthing1:
job := Somthing1{}
job = input.(Somthing1)
queueResults(job)
case Somthing2:
stats := Somthing2{}
stats = input.(Somthing2)
queueStatsRes(stats)
default:
}
This does not work. When Printing the type of input
after Unmarshaling
it I get map[string]interface{}
(?!?)
and even stranger than that, the map key is the string I got and the map value is empty.
I did some other attempts like:
func typeAssert(msg string) {
var input interface{}
json.Unmarshal([]byte(msg), &input)
switch v := input.(type){
case Somthing1:
v = input.(Somthing1)
queueResults(v)
case Somthing2:
v = input.(Somthing2)
queueStatsRes(v)
default:
}
and also tried writing the switch like was explained in this answer: Golang: cannot type switch on non-interface value
switch v := interface{}(input).(type)
still with no success...
Any ideas?
The default types that the json
package Unmarshals into are shown in the Unmarshal
function documentation
bool, for JSON booleans
float64, for JSON numbers
string, for JSON strings
[]interface{}, for JSON arrays
map[string]interface{}, for JSON objects
nil for JSON null
Since you're unmarshaling into an interface{}
, the returned types will only be from that set. The json
package doesn't know about Something1
and Something2
. You either need to convert from the map[string]interface{}
that the json object is being unmarshaled into, or unmarshal directly into the struct type you want.
If you don't want to do unpack the data from a generic interface, or somehow tag the data so you know what type to expect, you could iteratively take the json and try to unmarshal it into each type you want.
You can even pack those into a wrapper struct to do the unmarshaling for you:
type Something1 struct {
Thing string `json:"thing"`
OtherThing int64 `json:"other_thing"`
}
type Something2 struct {
Croc int `json:"croc"`
Odile bool `json:"odile"`
}
type Unpacker struct {
Data interface{}
}
func (u *Unpacker) UnmarshalJSON(b []byte) error {
smth1 := &Something1{}
err := json.Unmarshal(b, smth1)
// no error, but we also need to make sure we unmarshaled something
if err == nil && smth1.Thing != "" {
u.Data = smth1
return nil
}
// abort if we have an error other than the wrong type
if _, ok := err.(*json.UnmarshalTypeError); err != nil && !ok {
return err
}
smth2 := &Something2{}
err = json.Unmarshal(b, smth2)
if err != nil {
return err
}
u.Data = smth2
return nil
}
http://play.golang.org/p/Trwd6IShDW
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