是否可以在运行中将JSON部分反序列化为结构？

I need to integrate with an API that returns loads of elements in its response.

Is it possible to cherry-pick just the fields I want with go's json library or do I need to deserialise the entire response?

Yes.

Here's an example of having 2 fields in json and only decoding one:

jsonString := `{"a": 1, "b": 2}`
var rec struct {
    A int `json:"a"`
}
err := json.Unmarshal([]byte(jsonString), &rec)
if err != nil {
    log.Fatalf("json.Unmarshal() failed with '%s'
", err)
}
fmt.Printf("rec: %+v
", rec)

When run it prints:

rec: {A:1}

i.e. field "a" in json was decoded and field "b" was discarded.

See https://play.golang.org/p/89tu-ZC4pR for full example.