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2022/4/28

Golang 寫出JSON回應 write out JSON response

Go http handler寫出JSON回應的方式如下。


範例

使用http.ResponseWriter.Header().Set()設定回應的Content-Type為application/json。

呼叫json.NewEncoder()傳入ResponseWriter物件取得json.Encoder，其會將encode結果透過傳入的writer寫出。

接著調用json.Encoder.Encode()傳入struct轉為JSON並寫到輸出串流。

main.go

package main

import (
    "encoding/json"
    "net/http"
)

type Employee struct {
    Id   int
    Name string
    Age  int
}

func main() {
    http.HandleFunc("/employee", func(rw http.ResponseWriter, r *http.Request) {
        switch r.Method {
        case http.MethodGet:
            emp := Employee{
                Id:   1,
                Name: "john",
                Age:  33,
            }
            rw.Header().Set("Content-Type", "application/json")
            json.NewEncoder(rw).Encode(emp) // use ReponseWriter with encoder to write json encoding of emp to stream.
        default:
            http.Error(rw, "Method not allowed", http.StatusMethodNotAllowed)
        }
    })
    http.ListenAndServe(":8080", nil)
}

github。


測試

啟動應用程式後在命令列以cURL執行curl -v "http://localhost:8080/employee"。

$ curl -v "http://localhost:8080/employee"
*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> GET /employee HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Content-Type: application/json
< Date: Thu, 28 Apr 2022 15:02:42 GMT
< Content-Length: 32
<
{"Id":1,"Name":"john","Age":33}

從上可看到回應的Content-Type為application/json；回應內容為{"Id":1,"Name":"john","Age":33}。


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