如何使用Go从JSON文件读取一个值

Question

I an new to programming in Go so apologies if this is something obvious. I have a JSON file named foo.json:

{"type":"fruit","name":"apple","color":"red"}

and I am writing a Go program that has to do something when the "name" value in the JSON file is "apple". It needs no other information from that JSON file as that file is used for a completely different purpose in another area of the code.

I have read documentation on Decode() and Unmarshal() and abut 30 different web pages describing how to read the whole file into structures, etc. but it all seems extremely complicated for what I want to do which is just write the correct code to implement the first 2 lines of this pseudo-code:

file, _ := os.Open("foo.json")
name = file["name"]
if (name == "apple") {
    do stuff
}

such that I end up with a Go variable named name that contains the string value apple. What is the right way to do this in Go?

Answer 1

The easiest method to do what you want is to decode into a struct.

Provided the format remains similar to {"type":"fruit","name":"apple","color":"red"}

type Name struct {
    Name string `json:"name"`
}

var data []byte
data, _ = ioutil.ReadFile("foo.json")

var str Name
_ = json.Unmarshal(data, &str)

if str.Name == "apple" {
    // Do Stuff
}

Your other option is to use third party libraries such as gabs or jason.

Gabs :

jsonParsed, err := gabs.ParseJSON(data)
name, ok := jsonParsed.Path("name").Data().(string)

Jason :

v, _ := jason.NewObjectFromBytes(data)
name, _ := v.GetString("name")

---

Update :

The structure

type Name struct {
    Name string `json:"name"`
}

is the json equivalent of {"name":"foo"}.

So unmarshaling won't work for the following json with different formats.

[{"name":"foo"}]

{"bar":{"name":"foo"}}

PS : As mentioned by W.K.S. In your case an anonymous struct would suffice since you're not using this structure for anything else.