Golang in sixty seconds — consuming JSON

My previous article spoke about Marshalling JSON into a Go type. Let's look at how you can do the opposite — Unmarshalling

type person struct {
  Name string `json:"First name"`
  age  int
}
func main() {
  j := `{"First name":"Mike","age":25}`
  p := person{}
  json.Unmarshal([]byte(j), &p)
  fmt.Println(p) // {Mike 0}
}

To unmarshal the JSON, you first need to create an instance of a type ( pin the example above), then pass the pointer &p to the Unmarshal function along with the JSON data as a byte slice. Similar to the json.Marshal function, it will only use exported fields, so our output has the nil value for an int (0).

You can use an empty interface in order to marshal or unmarshal data without specifically knowing what it will look like. I've found this useful for services which pass metadata around without actually making use of it.

type person struct {
  Name     string `json:"First name"`
  age      int
  Metadata map[string]interface{} `json:"metadata"`
}
func main() {
  j := `{"First name":"Mike","age":25, "metadata": {"some":"stuff","things":[1,2,3]}}`
  p := person{}
  json.Unmarshal([]byte(j), &p)
  fmt.Println(p) // {Mike 0 map[some:stuff things:[1 2 3]]}
}

You can see this example here.

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