如何将我的二维字符串切片转换为[] byte？

I have created a 2d slices and populated it from backend database but as json.Unmarshal accepts only []byte as first parameter how can I typecast my 2d slice to []byte.

Here is the sample code for reference as I can't share internal code:

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
)

//User sjd
type User struct {
    EmailList [][]string `json:"emailList"`
}

func listHandler(w http.ResponseWriter, r *http.Request) {
    reqBody, _ := ioutil.ReadAll(r.Body)
    var user User
    json.Unmarshal(reqBody, &user)
    el := user.EmailList 
    keys := make([][]string, 0)
    json.Unmarshal([]byte(el), &keys) //this line not working because []byte(el) not possible
    fmt.Println(keys)
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(http.StatusOK)
    w.Write([]byte(el))//this line not working because []byte(el) not possible
}

func main() {
    http.HandleFunc("/", listHandler)
    http.ListenAndServe(":8080", nil)
}

Sample request:

{
    "emailList": [
        [
            "akki@gmail.com",
            "bakki@gmail.com"
        ],
        [
            "lakki@gmail.com",
            "jakki@gmail.com"
        ]
    ]
}

Unmarshal JSON as []byte to user. Marshal user.EmailList to JSON as []byte. For example,

package main

import (
    "encoding/json"
    "fmt"
    "os"
)

type User struct {
    EmailList [][]string `json:"emailList"`
}

func main() {
    // rBody, err := ioutil.ReadAll(r.Body)
    rBody := []byte(`
{
    "emailList": [
        [
            "akki@gmail.com",
            "bakki@gmail.com"
        ],
        [
            "lakki@gmail.com",
            "jakki@gmail.com"
        ]
    ]
}
    `)
    fmt.Println(string(rBody))

    var user User
    err := json.Unmarshal(rBody, &user)
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return
    }
    fmt.Println(user.EmailList)

    wData, err := json.Marshal(user.EmailList) // wData is []byte
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return
    }
    fmt.Println(wData) // wData is []byte
    fmt.Println(string(wData))
    // _, err = w.Write(wData)
}

Playground: https://play.golang.org/p/S3HWiTqz--B

Output:

{
    "emailList": [
        [
            "akki@gmail.com",
            "bakki@gmail.com"
        ],
        [
            "lakki@gmail.com",
            "jakki@gmail.com"
        ]
    ]
}

[[akki@gmail.com bakki@gmail.com] [lakki@gmail.com jakki@gmail.com]]
[91 91 34 97 107 107 105 64 103 109 97 105 108 46 99 111 109 34 44 34 98 97 107 107 105 64 103 109 97 105 108 46 99 111 109 34 93 44 91 34 108 97 107 107 105 64 103 109 97 105 108 46 99 111 109 34 44 34 106 97 107 107 105 64 103 109 97 105 108 46 99 111 109 34 93 93]
[["akki@gmail.com","bakki@gmail.com"],["lakki@gmail.com","jakki@gmail.com"]]