I'm trying read JSON data from web, but that code returns empty result. I'm not sure what I'm doing wrong here.
package main
import "os"
import "fmt"
import "net/http"
import "io/ioutil"
import "encoding/json"
type Tracks struct {
Toptracks []Toptracks_info
}
type Toptracks_info struct {
Track []Track_info
Attr []Attr_info
}
type Track_info struct {
Name string
Duration string
Listeners string
Mbid string
Url string
Streamable []Streamable_info
Artist []Artist_info
Attr []Track_attr_info
}
type Attr_info struct {
Country string
Page string
PerPage string
TotalPages string
Total string
}
type Streamable_info struct {
Text string
Fulltrack string
}
type Artist_info struct {
Name string
Mbid string
Url string
}
type Track_attr_info struct {
Rank string
}
func get_content() {
// json data
url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"
res, err := http.Get(url)
if err != nil {
panic(err.Error())
}
body, err := ioutil.ReadAll(res.Body)
if err != nil {
panic(err.Error())
}
var data Tracks
json.Unmarshal(body, &data)
fmt.Printf("Results: %v\n", data)
os.Exit(0)
}
func main() {
get_content()
}
The results from json.Unmarshal
(into var data interface{}
) do not directly match your Go type and variable declarations. For example,
package main
import (
"encoding/json"
"fmt"
"io/ioutil"
"net/http"
"os"
)
type Tracks struct {
Toptracks []Toptracks_info
}
type Toptracks_info struct {
Track []Track_info
Attr []Attr_info
}
type Track_info struct {
Name string
Duration string
Listeners string
Mbid string
Url string
Streamable []Streamable_info
Artist []Artist_info
Attr []Track_attr_info
}
type Attr_info struct {
Country string
Page string
PerPage string
TotalPages string
Total string
}
type Streamable_info struct {
Text string
Fulltrack string
}
type Artist_info struct {
Name string
Mbid string
Url string
}
type Track_attr_info struct {
Rank string
}
func get_content() {
// json data
url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"
url += "&limit=1" // limit data for testing
res, err := http.Get(url)
if err != nil {
panic(err.Error())
}
body, err := ioutil.ReadAll(res.Body)
if err != nil {
panic(err.Error())
}
var data interface{} // TopTracks
err = json.Unmarshal(body, &data)
if err != nil {
panic(err.Error())
}
fmt.Printf("Results: %v\n", data)
os.Exit(0)
}
func main() {
get_content()
}
Output:
Results: map[toptracks:map[track:map[name:Get Lucky (feat. Pharrell Williams) listeners:1863 url:http://www.last.fm/music/Daft+Punk/_/Get+Lucky+(feat.+Pharrell+Williams) artist:map[name:Daft Punk mbid:056e4f3e-d505-4dad-8ec1-d04f521cbb56 url:http://www.last.fm/music/Daft+Punk] image:[map[#text:http://userserve-ak.last.fm/serve/34s/88137413.png size:small] map[#text:http://userserve-ak.last.fm/serve/64s/88137413.png size:medium] map[#text:http://userserve-ak.last.fm/serve/126/88137413.png size:large] map[#text:http://userserve-ak.last.fm/serve/300x300/88137413.png size:extralarge]] @attr:map[rank:1] duration:369 mbid: streamable:map[#text:1 fulltrack:0]] @attr:map[country:Netherlands page:1 perPage:1 totalPages:500 total:500]]]
Your Problem were the slice declarations in your data structs
(except for Track
, they shouldn't be slices...). This was compounded by some rather goofy fieldnames in the fetched json file, which can be fixed via structtags, see godoc.
The code below parsed the json successfully. If you've further questions, let me know.
package main
import "fmt"
import "net/http"
import "io/ioutil"
import "encoding/json"
type Tracks struct {
Toptracks Toptracks_info
}
type Toptracks_info struct {
Track []Track_info
Attr Attr_info `json: "@attr"`
}
type Track_info struct {
Name string
Duration string
Listeners string
Mbid string
Url string
Streamable Streamable_info
Artist Artist_info
Attr Track_attr_info `json: "@attr"`
}
type Attr_info struct {
Country string
Page string
PerPage string
TotalPages string
Total string
}
type Streamable_info struct {
Text string `json: "#text"`
Fulltrack string
}
type Artist_info struct {
Name string
Mbid string
Url string
}
type Track_attr_info struct {
Rank string
}
func perror(err error) {
if err != nil {
panic(err)
}
}
func get_content() {
url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"
res, err := http.Get(url)
perror(err)
defer res.Body.Close()
decoder := json.NewDecoder(res.Body)
var data Tracks
err = decoder.Decode(&data)
if err != nil {
fmt.Printf("%T\n%s\n%#v\n",err, err, err)
switch v := err.(type){
case *json.SyntaxError:
fmt.Println(string(body[v.Offset-40:v.Offset]))
}
}
for i, track := range data.Toptracks.Track{
fmt.Printf("%d: %s %s\n", i, track.Artist.Name, track.Name)
}
}
func main() {
get_content()
}
You need upper case property names in your structs in order to be used by the json packages.
Upper case property names are exported properties
. Lower case property names are not exported.
You also need to pass the your data object by reference (&data
).
package main
import "os"
import "fmt"
import "net/http"
import "io/ioutil"
import "encoding/json"
type tracks struct {
Toptracks []toptracks_info
}
type toptracks_info struct {
Track []track_info
Attr []attr_info
}
type track_info struct {
Name string
Duration string
Listeners string
Mbid string
Url string
Streamable []streamable_info
Artist []artist_info
Attr []track_attr_info
}
type attr_info struct {
Country string
Page string
PerPage string
TotalPages string
Total string
}
type streamable_info struct {
Text string
Fulltrack string
}
type artist_info struct {
Name string
Mbid string
Url string
}
type track_attr_info struct {
Rank string
}
func get_content() {
// json data
url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=Netherlands"
res, err := http.Get(url)
if err != nil {
panic(err.Error())
}
body, err := ioutil.ReadAll(res.Body)
if err != nil {
panic(err.Error())
}
var data tracks
json.Unmarshal(body, &data)
fmt.Printf("Results: %v\n", data)
os.Exit(0)
}
func main() {
get_content()
}
Source: Stackoverflow.com