Example
Let's assume we have the following struct that defines a City type:
type City struct {
Name string
Temperature int
}
We can encode/decode City values using the encoding/json package.
First of all, we need to use the Go metadata to tell the encoder the correspondence between the struct fields and the JSON keys.
type City struct {
Name string `json:"name"`
Temperature int `json:"temp"`
// IMPORTANT: only exported fields will be encoded/decoded
// Any field starting with a lower letter will be ignored
}
To keep this example simple, we'll declare an explicit correspondence between the fields and the keys. However, you can use several variants of the json: metadata as explained in the docs.
IMPORTANT: Only exported fields (fields with capital name) will be serialized/deserialized. For example, if you name the field temperature it will be ignored even if you set the json metadata.
Encoding
To encode a City struct, use json.Marshal as in the basic example:
// data to encode
city := City{Name: "Rome", Temperature: 30}
// encode the data
bytes, err := json.Marshal(city)
if err != nil {
panic(err)
}
fmt.Println(string(bytes))
// {"name":"Rome","temp":30}
Decoding
To decode a City struct, use json.Unmarshal as in the basic example:
// data to decode
bytes := []byte(`{"name":"Rome","temp":30}`)
// initialize the container for the decoded data
var city City
// decode the data
// notice the use of &city to pass the pointer to city
if err := json.Unmarshal(bytes, &city); err != nil {
panic(err)
}
fmt.Println(city)
// {Rome 30}
