https://play.golang.org/p/6zegB4ved8T

gorilla_json_parse.go

package main

import (
	"encoding/json"
	"fmt"
	"path/filepath"
	"strings"
)

type Input struct {
	Key string `json:"key"`
}

type Child map[string]Child

func (c Child) Push(entry string) Child {
	if _, ok := c[entry]; !ok {
		c[entry] = make(Child)
	}
	return c[entry]
}

type Output struct {
	Name  string    `json:"name,omitempty"`
	Child []*Output `json:"child,omitempty"`
}

func (c Child) Conv() []*Output {
	if c == nil {
		return nil
	}
	ret := []*Output{}
	for k, v := range c {
		ret = append(ret, &Output{Name: k, Child: v.Conv()})
	}
	return ret
}

func main() {
	inputs := []*Input{}
	err := json.Unmarshal(test, &inputs)
	if err != nil {
		println(err.Error())
	}
	root := make(Child)
	for _, input := range inputs {
		curr := root
		for _, e := range strings.Split(input.Key, string(filepath.Separator)) {
			curr = curr.Push(e)
		}
	}
	b, err := json.Marshal(root.Conv())
	if err != nil {
		println(err.Error())
	}
	fmt.Println(string(b))
}

var test = []byte(`
[
  {"key":"a/b/c.json"},
  {"key":"a/b/d.json"},
  {"key":"b/c/f.json"},
  {"key":"b/f/g.json"},
  {"key":"x/y/z/"}
]`)