Golangでjsonを扱う

01 json_sample.json

{
  "id" : 1,
  "author" : "hogefuga",
  "content" : "Hellooooooooo!!",
  "comment" : {
    "comment_id" : 11,
    "message" : "very gooood"
  },
  "books" : [
    {
      "book_id" : 23,
      "title"  : "hogefuga"
    },
    {
      "book_id" : 54,
      "title"  : "wahahahahaha"
    },
    {
      "book_id" : 76,
      "title"  : "ohhhnoooo"
    }
  ]
}

02 json_read_write.go

package main

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

type Post struct {
        Id         int       `json:"id"`
        Author     string    `json:"author"`
        Content    string    `json:"content"`
        Comment    Comment   `json:"comment"`
        Books      []Book    `json:"books"`
}
type Comment struct {
        Comment_id int       `json:"comment_id"`
        Message    string    `json:"message"`
}
type Book struct {
        Book_id    int       `json:"book_id"`
        Title      string    `json:"title"`
}

func main() {
        // read json
        fmt.Println("===== Read json =====")
        json_file, err := os.Open("./json_sample.json")
        if err != nil {
                fmt.Println("Error opening", err)
                return
        }
        defer json_file.Close()

        json_data, err := ioutil.ReadAll(json_file)
        if err != nil {
                fmt.Println("Error reading", err)
                return
        }

        var post_read Post
        json.Unmarshal(json_data, &post_read)
        fmt.Println(post_read)
        fmt.Println(post_read.Comment.Message)
        fmt.Println(post_read.Books[2].Title)

        // write json
        fmt.Println("===== Write json =====")
        post_write := Post {
                Id : 11111,
                Author : "toriyama akira",
                Comment : Comment {
                        Comment_id : 999999,
                        Message : "sugeeeeeee",
                },
                Books : []Book {
                        Book {
                                Book_id : 1004,
                                Title : "naushika",
                        },
                        Book {
                                Book_id : 2006,
                                Title : "akira",
                        },
                        Book {
                                Book_id : 4005,
                                Title : "inachu",
                        },
                },
        }

        fmt.Println(post_write)
        output, err := json.MarshalIndent(&post_write, "", "\t")
        if err != nil {
                fmt.Println("Error marshalling", err)
                return
        }
        err = ioutil.WriteFile("json_output.json", output, 0644)
        if err != nil {
                fmt.Println("Error write file", err)
                return
        }
}

03 program result

===== Read json =====
{1 hogefuga Hellooooooooo!! {11 very gooood} [{23 hogefuga} {54 wahahahahaha} {76 ohhhnoooo}]}
very gooood
ohhhnoooo
===== Write json =====
{11111 toriyama akira  {999999 sugeeeeeee} [{1004 naushika} {2006 akira} {4005 inachu}]}

04 json_output.json

{
        "id": 11111,
        "author": "toriyama akira",
        "content": "",
        "comment": {
                "comment_id": 999999,
                "message": "sugeeeeeee"
        },
        "books": [
                {
                        "book_id": 1004,
                        "title": "naushika"
                },
                {
                        "book_id": 2006,
                        "title": "akira"
                },
                {
                        "book_id": 4005,
                        "title": "inachu"
                }
        ]
}