为什么golang不封送json对象？ [重复]

I wonder why the following didn't marshall to json successfully? I am trying to use a very simple example to learn json package.

package main

import (
    "encoding/json"
    "fmt"
)

type Message struct {
    username string `json:"name"`
    message  string `json:"message"`
}

func main() {
    var m = Message{
        username: "hello",
        message:  "world",
    }

    js, _ := json.Marshal(m)

    fmt.Println(m)
    fmt.Println(string(js))
}

</div>

username
message

start with a lowercase letter, meaning they are unexported (think private), and so are not visible to the encoding/json package. You need to export your fields, or implement the MarshalJSON() ([]byte, error) method and do it yourself.