Go provides encoding/json packages to easily process JSON data. 1. Use json.Marshal to encode the Go structure or map into JSON. The structure field must start with capital letters and specify the key name through the json:"name" tag. Omitempty can make the zero-value field omitted; 2. Use json.Unmarshal to decode the JSON data into a Go variable, and a variable pointer must be passed in order to modify the value; 3. For JSON with unknown structure, it can be decoded into map[string]interface{} or interface{}, but type assertions are required when accessing; 4. When processing large JSON files or streaming data, use json.Encoder and json.Decoder can achieve efficient incremental processing to avoid loading all data at once. Always check for errors to ensure that JSON is formatted correctly and has type matching, Go's JSON support is suitable for scenarios such as API development, configuration reads, and data processing.
Working with JSON in Go is straightforward thanks to the built-in encoding/json package. Go provides easy ways to encode (marshal) Go data structures into JSON and decode (unmarshal) JSON data into Go values.
Here's how you typically work with JSON in Go:
1. Encoding (Go → JSON) with json.Marshal
You use json.Marshal to convert Go structs or maps into JSON.
package main
import (
"encoding/json"
"fmt"
)
type Person struct {
Name string `json:"name"`
Age int `json:"age"`
Email string `json:"email,omitempty"`
}
func main() {
p := Person{Name: "Alice", Age: 30}
data, err := json.Marshal(p)
if err != nil {
panic(err)
}
fmt.Println(string(data)) // {"name":"Alice","age":30}
}- The
json:"name"tag tells Go what the JSON key should be. -
omitemptymeans the field will be omitted if it has a zero value (eg, empty string, 0, nil).
2. Decoding (JSON → Go) with json.Unmarshal
Use json.Unmarshal to parse JSON data into a struct or map.
jsonData := `{"name": "Bob", "age": 25, "email": "bob@example.com"}`
var p Person
err := json.Unmarshal([]byte(jsonData), &p)
if err != nil {
panic(err)
}
fmt.Printf("% v\n", p) // {Name:Bob Age:25 Email:bob@example.com}Note: You must pass a pointer to the variable (
&p) soUnmarshalcan modify it.
3. Working with Dynamic or Unknown JSON
If you don't know the structure of the JSON, you can use map[string]interface{} or interface{} .
var data map[string]interface{}
err := json.Unmarshal([]byte(jsonData), &data)
if err != nil {
panic(err)
}
fmt.Println(data["name"]) // Bob You can also decode into []interface{} for arrays.
?? Be careful: you'll need type assertions when accessing values.
4. Streaming JSON: json.Encoder and json.Decoder
For handling large JSON files or HTTP streams, use json.Encoder and json.Decoder .
Writing JSON to an HTTP response or file:
encoder := json.NewEncoder(writer) // eg, http.ResponseWriter or os.File err := encoder.Encode(person)
Reading JSON from a request body or file:
decoder := json.NewDecoder(reader) var person Person err := decoder.Decode(&person)
These are efficient because they process data incrementally, not all at once.
Key Tips
- Struct fields must be exported (start with a capital letter) to be JSON-marshalable.
- Use struct tags to control field names, omitempty, string formatting (eg,
json:",string"for numbers-as-strings). -
time.Timefields can be serialized automatically if formatted properly. - Always check for errors — malformed JSON or type mismatches will return errors during unmarshaling.
Basically, Go's encoding/json gives you a clean, efficient way to handle JSON whether you're building APIs, reading config files, or processing data. Just define your structs, use tags wisely, and lean on Marshal / Unmarshal or the streaming Encoder / Decoder as needed.
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