JSON encode of array of own struct - arrays

Question

I try to read a directory and make a JSON string out of the file entries. But the json.encoder.Encode() function returns only empty objects. For test I have two files in a tmp dir:
test1.js test2.js
The go program is this:
package main
import (
"encoding/json"
"fmt"
"os"
"path/filepath"
"time"
)
type File struct {
name string
timeStamp int64
}
func main() {
files := make([]File, 0, 20)
filepath.Walk("/home/michael/tmp/", func(path string, f os.FileInfo, err error) error {
if f == nil {
return nil
}
name := f.Name()
if len(name) > 3 {
files = append(files, File{
name: name,
timeStamp: f.ModTime().UnixNano() / int64(time.Millisecond),
})
// grow array if needed
if cap(files) == len(files) {
newFiles := make([]File, len(files), cap(files)*2)
for i := range files {
newFiles[i] = files[i]
}
files = newFiles
}
}
return nil
})
fmt.Println(files)
encoder := json.NewEncoder(os.Stdout)
encoder.Encode(&files)
}
And the out that it produces is:
[{test1.js 1444549471481} {test2.js 1444549481017}]
[{},{}]
Why is the JSON string empty?

Answer 1

It doesn't work because none of the fields in the File struct are exported.
The following works just fine:
package main
import (
"encoding/json"
"fmt"
"os"
"path/filepath"
"time"
)
type File struct {
Name string
TimeStamp int64
}
func main() {
files := make([]File, 0, 20)
filepath.Walk("/tmp/", func(path string, f os.FileInfo, err error) error {
if f == nil {
return nil
}
name := f.Name()
if len(name) > 3 {
files = append(files, File{
Name: name,
TimeStamp: f.ModTime().UnixNano() / int64(time.Millisecond),
})
// grow array if needed
if cap(files) == len(files) {
newFiles := make([]File, len(files), cap(files)*2)
for i := range files {
newFiles[i] = files[i]
}
files = newFiles
}
}
return nil
})
fmt.Println(files)
encoder := json.NewEncoder(os.Stdout)
encoder.Encode(&files)
}