如何在解析 XML 时获取一个空数组？

huangapple
go评论103阅读模式
英文:

How to getting an empty array when parsing XML?

问题

我被委托编写一个Go实用程序，它接受一个XML文件，解析它，并以JSON格式返回。

以下是XML的示例：

  1. <?xml version="1.0" encoding="utf-8"?>
  2. <tracks clid="020">
  3.   <track uuid="551" category="s" route="8" vehicle_type="trolleybus" >
  4.     <point
  5.       latitude="53.61491"
  6.       longitude="55.90922"
  7.       avg_speed="24"
  8.       direction="270"
  9.       time="13122022:072116"
  10.     />
  11.   </track>
  12.   <track uuid="552" category="s" route="6" vehicle_type="trolleybus">
  13.     <point
  14.       latitude="53.68321"
  15.       longitude="57.90922"
  16.       avg_speed="42"
  17.       direction="181"
  18.       time="13122022:072216"
  19.     />
  20.   </track>
  21. </tracks>

我编写了以下代码：

  1. package main
  3. import (
  4. 	"encoding/json"
  5. 	"encoding/xml"
  6. 	"fmt"
  7. )
  9. type Tracks struct {
  10. 	XMLName xml.Name `xml:"tracks" json:"-"`
  11. 	Clid    string   `xml:"clid,attr" json:"clid"`
  12. 	Tracks  []Track  `xml:"track" json:"track_list"`
  13. }
  15. type Track struct {
  16. 	XMLName     xml.Name `xml:"tracks"`
  17. 	Uuid        string   `xml:"uuid,attr" json:"uuid"`
  18. 	Category    string   `xml:"category,attr" json:"category"`
  19. 	Route       string   `xml:"route,attr" json:"route"`
  20. 	VehicleType string   `xml:"vehicle_type,attr" json:"vehicle_type"`
  21. 	Point       Point    `xml:"point" json:"point"`
  22. }
  24. type Point struct {
  25. 	Latitude  string `xml:"latitude,attr" json:"latitude"`
  26. 	Longitude string `xml:"longitude,attr" json:"longitude"`
  27. 	AvgSpeed  string `xml:"avg_speed,attr" json:"avg_speed"`
  28. 	Direction string `xml:"direction,attr" json:"direction"`
  29. 	Time      string `xml:"time,attr" json:"time"`
  30. }
  32. func main() {
  33. 	rawXmlData := `
  34. 		<?xml version="1.0" encoding="utf-8"?>
  35. 		<tracks clid="020">
  36. 			<track uuid="551" category="s" route="8" vehicle_type="trolleybus">
  37. 				<point latitude="53.61491" longitude="55.90922" avg_speed="24" direction="270" time="13122022:072116"/>
  38. 			</track>
  39. 			<track uuid="552" category="s" route="6" vehicle_type="trolleybus">
  40. 				<point latitude="53.68321" longitude="57.90922" avg_speed="42" direction="181" time="13122022:072216"/>
  41. 			</track>
  42. 		</tracks>
  43. 	`
  45. 	var tracks Tracks
  47. 	err := xml.Unmarshal([]byte(rawXmlData), &tracks)
  48. 	if err != nil {
  49. 		log.Fatal(err)
  50. 	}
  52. 	jsonData, err := json.Marshal(tracks)
  53. 	if err != nil {
  54. 		log.Fatal(err)
  55. 	}
  57. 	fmt.Printf(string(jsonData))
  58. }

但是，不幸的是，它不起作用。我在控制台中得到以下错误：

  1. 2009/11/10 23:00:00 expected element type <tracks> but have <track>

我做错了什么？我该如何解决这个问题？

英文:

I was tasked with writing a Go utility that takes an XML file, parses it, and returns it in JSON.

Here is an example of the XML:

  1. &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
  2. &lt;tracks clid=&quot;020&quot;&gt;
  3.   &lt;track uuid=&quot;551&quot; category=&quot;s&quot; route=&quot;8&quot; vehicle_type=&quot;trolleybus&quot; &gt;
  4.     &lt;point
  5.       latitude=&quot;53.61491&quot;
  6.       longitude=&quot;55.90922&quot;
  7.       avg_speed=&quot;24&quot;
  8.       direction=&quot;270&quot;
  9.       time=&quot;13122022:072116&quot;
  10.     /&gt;
  11.   &lt;/track&gt;
  12.   &lt;track uuid=&quot;552&quot; category=&quot;s&quot; route=&quot;6&quot; vehicle_type=&quot;trolleybus&quot;&gt;
  13.     &lt;point
  14.       latitude=&quot;53.68321&quot;
  15.       longitude=&quot;57.90922&quot;
  16.       avg_speed=&quot;42&quot;
  17.       direction=&quot;181&quot;
  18.       time=&quot;13122022:072216&quot;
  19.     /&gt;
  20.   &lt;/track&gt;
  21. &lt;/tracks&gt;

I wrote the following code:

  1. package main
  3. import (
  4. 	&quot;encoding/json&quot;
  5. 	&quot;encoding/xml&quot;
  6. 	&quot;fmt&quot;
  7. )
  9. type Tracks struct {
  10. 	XMLName xml.Name `xml:&quot;tracks&quot; json:&quot;-&quot;`
  11. 	Clid    string   `xml:&quot;clid,attr&quot; json:&quot;clid&quot;`
  12. 	Tracks  []Track  `xml:&quot;track&quot; json:&quot;track_list&quot;`
  13. }
  15. type Track struct {
  16. 	XMLName     xml.Name `xml:&quot;tracks&quot;`
  17. 	Uuid        string   `xml:&quot;uuid,attr&quot; json:&quot;uuid&quot;`
  18. 	Category    string   `xml:&quot;category,attr&quot; json:&quot;category&quot;`
  19. 	Route       string   `xml:&quot;route,attr&quot; json:&quot;route&quot;`
  20. 	VehicleType string   `xml:&quot;vehicle_type,attr&quot; json:&quot;vehicle_type&quot;`
  21. 	Point       Point    `xml:&quot;point&quot; json:&quot;point&quot;`
  22. }
  24. type Point struct {
  25. 	Latitude  string `xml:&quot;latitude,attr&quot; json:&quot;latitude&quot;`
  26. 	Longitude string `xml:&quot;longitude,attr&quot; json:&quot;longitude&quot;`
  27. 	AvgSpeed  string `xml:&quot;avg_speed,attr&quot; json:&quot;avg_speed&quot;`
  28. 	Direction string `xml:&quot;direction,attr&quot; json:&quot;direction&quot;`
  29. 	Time      string `xml:&quot;time,attr&quot; json:&quot;time&quot;`
  30. }
  32. func main() {
  33. 	rawXmlData := `
  34. 		&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
  35. 		&lt;tracks clid=&quot;020&quot;&gt;
  36. 			&lt;track uuid=&quot;551&quot; category=&quot;s&quot; route=&quot;8&quot; vehicle_type=&quot;trolleybus&quot;&gt;
  37. 				&lt;point latitude=&quot;53.61491&quot; longitude=&quot;55.90922&quot; avg_speed=&quot;24&quot; direction=&quot;270&quot; time=&quot;13122022:072116&quot;/&gt;
  38. 			&lt;/track&gt;
  39. 			&lt;track uuid=&quot;552&quot; category=&quot;s&quot; route=&quot;6&quot; vehicle_type=&quot;trolleybus&quot;&gt;
  40. 				&lt;point latitude=&quot;53.68321&quot; longitude=&quot;57.90922&quot; avg_speed=&quot;42&quot; direction=&quot;181&quot; time=&quot;13122022:072216&quot;/&gt;
  41. 			&lt;/track&gt;
  42. 		&lt;/tracks&gt;
  43. 	`
  45. 	var tracks Tracks
  47. 	err := xml.Unmarshal([]byte(rawXmlData), &amp;tracks)
  48. 	if err != nil {
  49. 		log.Fatal(err)
  50. 	}
  52. 	jsonData, err := json.Marshal(tracks)
  53. 	if err != nil {
  54. 		log.Fatal(err)
  55. 	}
  57. 	fmt.Printf(string(jsonData))
  58. }

Go.dev

But, unfortunately, it doesn't work. I get the following in the console:

  1. 2009/11/10 23:00:00 expected element type &lt;tracks&gt; but have &lt;track&gt;

What am I doing wrong? How can I solve this problem?

答案1

得分: 2

我觉得我会将讨论转移到一个答案上，因为我认为你很接近了。正如我之前提到的，你需要检查xml.Unmarshal返回的错误。代码可能如下所示：

  1. if err := xml.Unmarshal([]byte(rawXmlData), &tracks); err != nil {
  2.     panic(err)
  3. }

现在你的代码中有有效的XML数据，我们可以生成有意义的错误；通过上述错误检查，运行你的代码会产生以下输出：

  1. panic: expected element type <tracks> but have <track>
  3. goroutine 1 [running]:
  4. main.main()
  5.         /home/lars/tmp/go/main.go:48 +0x12f

这是因为你的数据结构中有一个小错误；在Track结构体的定义中，你有：

  1. type Track struct {
  2.     XMLName     xml.Name `xml:"tracks"`
  3.     Uuid        string   `xml:"uuid,attr" json:"uuid"`
  4.     Category    string   `xml:"category,attr" json:"category"`
  5.     Route       string   `xml:"route,attr" json:"route"`
  6.     VehicleType string   `xml:"vehicle_type,attr" json:"vehicle_type"`
  7.     Point       Point    `xml:"point" json:"point"`
  8. }

你将XMLName属性的标签错误地标记为tracks，而应该是track：

  1. type Track struct {
  2.     XMLName     xml.Name `xml:"track"`
  3.     Uuid        string   `xml:"uuid,attr" json:"uuid"`
  4.     Category    string   `xml:"category,attr" json:"category"`
  5.     Route       string   `xml:"route,attr" json:"route"`
  6.     VehicleType string   `xml:"vehicle_type,attr" json:"vehicle_type"`
  7.     Point       Point    `xml:"point" json:"point"`
  8. }

最后，这与问题没有直接关系，但你应该避免将变量命名为error，因为那是内置的错误数据类型的名称。我会修改你对json.Marshal的调用，如下所示：

  1. jsonData, err := json.Marshal(tracks)
  2. if err != nil {
  3.     panic(err)
  4. }

你不需要在错误上使用panic()；这只是一种方便的方式来退出代码。

在进行这些更改后，如果我们编译并运行代码，我们会得到以下输出（使用jq格式化）：

  1. {
  2.   "clid": "020",
  3.   "track_list": [
  4.     {
  5.       "XMLName": {
  6.         "Space": "",
  7.         "Local": "track"
  8.       },
  9.       "uuid": "551",
  10.       "category": "s",
  11.       "route": "8",
  12.       "vehicle_type": "trolleybus",
  13.       "point": {
  14.         "latitude": "53.61491",
  15.         "longitude": "55.90922",
  16.         "avg_speed": "24",
  17.         "direction": "270",
  18.         "time": "13122022:072116"
  19.       }
  20.     },
  21.     {
  22.       "XMLName": {
  23.         "Space": "",
  24.         "Local": "track"
  25.       },
  26.       "uuid": "552",
  27.       "category": "s",
  28.       "route": "6",
  29.       "vehicle_type": "trolleybus",
  30.       "point": {
  31.         "latitude": "53.68321",
  32.         "longitude": "57.90922",
  33.         "avg_speed": "42",
  34.         "direction": "181",
  35.         "time": "13122022:072216"
  36.       }
  37.     }
  38.   ]
  39. }

请注意，你甚至不需要在结构体中使用XMLName元素；如果我们完全删除它，使得结构体如下所示：

  1. type Track struct {
  2.     Uuid        string `xml:"uuid,attr" json:"uuid"`
  3.     Category    string `xml:"category,attr" json:"category"`
  4.     Route       string `xml:"route,attr" json:"route"`
  5.     VehicleType string `xml:"vehicle_type,attr" json:"vehicle_type"`
  6.     Point       Point  `xml:"point" json:"point"`
  7. }

那么我们会得到以下输出（使用jq格式化）：

  1. {
  2.   "clid": "020",
  3.   "track_list": [
  4.     {
  5.       "uuid": "551",
  6.       "category": "s",
  7.       "route": "8",
  8.       "vehicle_type": "trolleybus",
  9.       "point": {
  10.         "latitude": "53.61491",
  11.         "longitude": "55.90922",
  12.         "avg_speed": "24",
  13.         "direction": "270",
  14.         "time": "13122022:072116"
  15.       }
  16.     },
  17.     {
  18.       "uuid": "552",
  19.       "category": "s",
  20.       "route": "6",
  21.       "vehicle_type": "trolleybus",
  22.       "point": {
  23.         "latitude": "53.68321",
  24.         "longitude": "57.90922",
  25.         "avg_speed": "42",
  26.         "direction": "181",
  27.         "time": "13122022:072216"
  28.       }
  29.     }
  30.   ]
  31. }
英文:

I thought I would move the discussion to an answer, since I think you're pretty close. As I mentioned, you need to check the error returned by xml.Unmarshal. That might look like this:

  1. 	if err := xml.Unmarshal([]byte(rawXmlData), &amp;tracks); err != nil {
  2. panic(err)
  3. }

Now that you have valid XML data in your code, we can produce meaningful errors; with the above error check in place, running your code produces:

  1. panic: expected element type &lt;tracks&gt; but have &lt;track&gt;
  2. goroutine 1 [running]:
  3. main.main()
  4. /home/lars/tmp/go/main.go:48 +0x12f

That's happening because of a minor typo in your data structures; in the definition of your Track struct, you have:

  1. type Track struct {
  2. XMLName     xml.Name `xml:&quot;tracks&quot;`
  3. Uuid        string   `xml:&quot;uuid,attr&quot; json:&quot;uuid&quot;`
  4. Category    string   `xml:&quot;category,attr&quot; json:&quot;category&quot;`
  5. Route       string   `xml:&quot;route,attr&quot; json:&quot;route&quot;`
  6. VehicleType string   `xml:&quot;vehicle_type,attr&quot; json:&quot;vehicle_type&quot;`
  7. Point       Point    `xml:&quot;point&quot; json:&quot;point&quot;`
  8. }

You've mis-tagged the XMLName attribute as tracks when it should be track:

  1. type Track struct {
  2. XMLName     xml.Name `xml:&quot;track&quot;`
  3. Uuid        string   `xml:&quot;uuid,attr&quot; json:&quot;uuid&quot;`
  4. Category    string   `xml:&quot;category,attr&quot; json:&quot;category&quot;`
  5. Route       string   `xml:&quot;route,attr&quot; json:&quot;route&quot;`
  6. VehicleType string   `xml:&quot;vehicle_type,attr&quot; json:&quot;vehicle_type&quot;`
  7. Point       Point    `xml:&quot;point&quot; json:&quot;point&quot;`
  8. }

Lastly -- and this isn't directly related to the problem -- you should avoid naming a variable error, because that's the name of the built-in data type of errors. I would modify your call to json.Marshal like this:

  1. 	jsonData, err := json.Marshal(tracks)
  2. if err != nil {
  3. panic(err)
  4. }

You don't need to panic() on errors; this is just a convenient way to bail out of the code.

With these changes in place, if we compile and run the code we get as output (formatted with jq):

  1. {
  2. &quot;clid&quot;: &quot;020&quot;,
  3. &quot;track_list&quot;: [
  4. {
  5. &quot;XMLName&quot;: {
  6. &quot;Space&quot;: &quot;&quot;,
  7. &quot;Local&quot;: &quot;track&quot;
  8. },
  9. &quot;uuid&quot;: &quot;551&quot;,
  10. &quot;category&quot;: &quot;s&quot;,
  11. &quot;route&quot;: &quot;8&quot;,
  12. &quot;vehicle_type&quot;: &quot;trolleybus&quot;,
  13. &quot;point&quot;: {
  14. &quot;latitude&quot;: &quot;53.61491&quot;,
  15. &quot;longitude&quot;: &quot;55.90922&quot;,
  16. &quot;avg_speed&quot;: &quot;24&quot;,
  17. &quot;direction&quot;: &quot;270&quot;,
  18. &quot;time&quot;: &quot;13122022:072116&quot;
  19. }
  20. },
  21. {
  22. &quot;XMLName&quot;: {
  23. &quot;Space&quot;: &quot;&quot;,
  24. &quot;Local&quot;: &quot;track&quot;
  25. },
  26. &quot;uuid&quot;: &quot;552&quot;,
  27. &quot;category&quot;: &quot;s&quot;,
  28. &quot;route&quot;: &quot;6&quot;,
  29. &quot;vehicle_type&quot;: &quot;trolleybus&quot;,
  30. &quot;point&quot;: {
  31. &quot;latitude&quot;: &quot;53.68321&quot;,
  32. &quot;longitude&quot;: &quot;57.90922&quot;,
  33. &quot;avg_speed&quot;: &quot;42&quot;,
  34. &quot;direction&quot;: &quot;181&quot;,
  35. &quot;time&quot;: &quot;13122022:072216&quot;
  36. }
  37. }
  38. ]
  39. }

Note that you don't even need that XMLName element in your structure; if we remove it completely so that we have:

  1. type Track struct {
  2. Uuid        string `xml:&quot;uuid,attr&quot; json:&quot;uuid&quot;`
  3. Category    string `xml:&quot;category,attr&quot; json:&quot;category&quot;`
  4. Route       string `xml:&quot;route,attr&quot; json:&quot;route&quot;`
  5. VehicleType string `xml:&quot;vehicle_type,attr&quot; json:&quot;vehicle_type&quot;`
  6. Point       Point  `xml:&quot;point&quot; json:&quot;point&quot;`
  7. }

Then we get as output (formatted with jq):

  1. {
  2. &quot;clid&quot;: &quot;020&quot;,
  3. &quot;track_list&quot;: [
  4. {
  5. &quot;uuid&quot;: &quot;551&quot;,
  6. &quot;category&quot;: &quot;s&quot;,
  7. &quot;route&quot;: &quot;8&quot;,
  8. &quot;vehicle_type&quot;: &quot;trolleybus&quot;,
  9. &quot;point&quot;: {
  10. &quot;latitude&quot;: &quot;53.61491&quot;,
  11. &quot;longitude&quot;: &quot;55.90922&quot;,
  12. &quot;avg_speed&quot;: &quot;24&quot;,
  13. &quot;direction&quot;: &quot;270&quot;,
  14. &quot;time&quot;: &quot;13122022:072116&quot;
  15. }
  16. },
  17. {
  18. &quot;uuid&quot;: &quot;552&quot;,
  19. &quot;category&quot;: &quot;s&quot;,
  20. &quot;route&quot;: &quot;6&quot;,
  21. &quot;vehicle_type&quot;: &quot;trolleybus&quot;,
  22. &quot;point&quot;: {
  23. &quot;latitude&quot;: &quot;53.68321&quot;,
  24. &quot;longitude&quot;: &quot;57.90922&quot;,
  25. &quot;avg_speed&quot;: &quot;42&quot;,
  26. &quot;direction&quot;: &quot;181&quot;,
  27. &quot;time&quot;: &quot;13122022:072216&quot;
  28. }
  29. }
  30. ]
  31. }

答案2

得分: 1

你好！以下是你要翻译的内容：

  1. type Track struct {
  2.     XMLName     xml.Name `xml:"tracks"`

应该是 "track" 而不是 "tracks"。

链接

英文: 
  1. type Track struct {
  2. XMLName     xml.Name `xml:&quot;tracks&quot;`

should be "track" not "tracks"

https://go.dev/play/p/kg-Dyep8Fv9

huangapple
  • 本文由 发表于 2022年12月13日 22:13:20
  • 转载请务必保留本文链接：https://go.coder-hub.com/74786207.html
  • go
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  • xml-parsing
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