File Operation Functions

The json package provides file operation functions, supporting file read/write and streaming I/O.

File Read Functions

LoadFromFile

Signature: func LoadFromFile(filePath string, cfg ...Config) (string, error)

Loads JSON data from a file.

Parameters

Name	Type	Required	Description
filePath	string	Yes	File path
cfg	Config	No	Optional configuration

data, err := json.LoadFromFile("config.json")
if err != nil {
    panic(err)
}
fmt.Println(data)

SaveToFile

Signature: func SaveToFile(filePath string, data any, cfg ...Config) error

Saves JSON data to a file.

Parameters

Name	Type	Required	Description
filePath	string	Yes	File path
data	any	Yes	Data to save
cfg	Config	No	Optional configuration

err := json.SaveToFile("output.json", map[string]any{
    "name": "Alice",
    "age":  30,
})
if err != nil {
    panic(err)
}

MarshalToFile

Signature: func MarshalToFile(filePath string, data any, cfg ...Config) error

Serializes data and writes it to a file.

Parameters

Name	Type	Required	Description
filePath	string	Yes	File path
data	any	Yes	Data to serialize
cfg	Config	No	Optional configuration

err := json.MarshalToFile("data.json", myStruct)

UnmarshalFromFile

Signature: func UnmarshalFromFile(filePath string, v any, cfg ...Config) error

Reads and deserializes data from a file.

Parameters

Name	Type	Required	Description
filePath	string	Yes	File path
v	any	Yes	Target object pointer
cfg	Config	No	Optional configuration

var config MyConfig
err := json.UnmarshalFromFile("config.json", &config)
if err != nil {
    panic(err)
}

LoadFromReader

Signature: func LoadFromReader(reader io.Reader, cfg ...Config) (string, error)

Loads JSON data from an io.Reader. Suitable for reading JSON from streaming sources like network connections, HTTP request bodies, etc.

Parameters

Name	Type	Required	Description
reader	io.Reader	Yes	Data source
cfg	Config	No	Optional configuration

// Read from HTTP response body
resp, _ := http.Get("https://api.example.com/data")
defer resp.Body.Close()
data, err := json.LoadFromReader(resp.Body)

// Read from a string
data, err = json.LoadFromReader(strings.NewReader(`{"name":"test"}`))

SaveToWriter

Signature: func SaveToWriter(writer io.Writer, data any, cfg ...Config) error

Writes JSON data to an io.Writer.

Parameters

Name	Type	Required	Description
writer	io.Writer	Yes	Output target
data	any	Yes	Data to write
cfg	Config	No	Optional configuration

var buf bytes.Buffer
err := json.SaveToWriter(&buf, map[string]any{"name": "test"})
if err != nil {
    panic(err)
}

See Also

• JSONL Processing Functions - ParseJSONL, StreamLinesInto and other newline-delimited JSON processing
• Encoding & Output Functions - Marshal, Unmarshal and other serialization operations
• Stream Processing - Stream processor details