json-unmarshal-sample.go

package main

import (
	"encoding/json"
	"errors"
	"io/ioutil"
	"log"
)

type Runner interface {
	Run()
}

type BaseJob struct {
	Name string `json:name`
	Type string `json:type`
}

type ShellJob struct {
	Name string `json:name`
	Type string `json:type`
	Cmd  string `json:grade`
}

func (j *ShellJob) Run() {
	log.Println("[ShellJob] command:", j.Cmd)
}

type TransferJob struct {
	Name string `json:name`
	Type string `json:type`
	From string `json:from`
	To   string `json:to`
}

func (j *TransferJob) Run() {
	log.Println("[TransferJob] from:", j.From, "to:", j.To)
}

func parseRunner(filepath string) (Runner, error) {
	fbytes, err := ioutil.ReadFile(filepath)
	if err != nil {
		return nil, err
	}
	var base BaseJob
	json.Unmarshal(fbytes, &base)
	log.Println("type:", base.Type)

	var result Runner
	switch base.Type {
	case "shell":
		var job ShellJob
		json.Unmarshal(fbytes, &job)
		result = &job
	case "transfer":
		var job TransferJob
		json.Unmarshal(fbytes, &job)
		result = &job
	default:
		return nil, errors.New("not matched. file: " + string(fbytes))
	}
	return result, nil
}

func main() {
	log.Println("vim-go")
	targets := []string{
		"./hoge.json",
		"./shell.json",
		"./transfer.json",
	}
	for _, filepath := range targets {
		runner, err := parseRunner(filepath)
		if err != nil {
			log.Println("[parseRunner err]", err)
		} else {
			runner.Run()
		}
	}
}

output.log

$ go run bind.go 
2020/02/07 12:16:54 vim-go
2020/02/07 12:16:54 [parseRunner err] open ./hoge.json: no such file or directory
2020/02/07 12:16:54 type: shell
2020/02/07 12:16:54 [ShellJob] command: sh -c date
2020/02/07 12:16:54 type: transfer
2020/02/07 12:16:54 [TransferJob] from: /tmp/log/*.csv to: my.remote.host

shell.json

{
  "name": "get-current",
  "cmd": "sh -c date",
  "type": "shell"
}

transfer.json

{
  "name": "copy-files-to-remote",
  "type": "transfer",
  "from": "/tmp/log/*.csv",
  "to": "my.remote.host"
}

https://golang.org/pkg/encoding/json/

このgistを書いたモチベーション

Web API叩いたときに帰ってくる結果の構成が変わるときに、
reflectionとかつかわないといけないかな(面倒なのでつかいたくない)と思ってた。
が、各json間で、共通部分(↑だと、name, type)だけもつstructでbindして判別するなどできることがわかった。