go xml parsing “doesn't see” any fields

2019-07-29 03:49发布

问题:

I must be missing something really obvious... Am trying to parse a simple XML file, following the example from ExampleUnmarshal() in here: http://golang.org/src/pkg/encoding/xml/example_test.go

As you'll see at the bottom of this, none of the attributes or child elements are being mapped - either direction - Marshal or Unmarshal. From what I can tell this is almost the exact same thing they are doing in example_test.go above (the only differences I can see are the that types in that test are within the scope of the function - which I tried, makes no diff, and they are using child elements and not attributes - except for id - but per doc name,attr should work afaict).

Code looks like this:

package main

import (
    "fmt"
    "encoding/xml"
    "io/ioutil"
)


type String struct {
    XMLName xml.Name `xml:"STRING"`
    lang  string   `xml:"lang,attr"`
    value  string   `xml:"value,attr"`
}

type Entry struct {
    XMLName xml.Name `xml:"ENTRY"`
    id      string  `xml:"id,attr"`
    strings []String 
}

type Dictionary struct {
    XMLName xml.Name `xml:"DICTIONARY"`
    thetype  string   `xml:"type,attr"`
    ignore  string   `xml:"ignore,attr"`
    entries []Entry  
}

func main() {

    dict := Dictionary{}

    b := []byte(`<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<DICTIONARY type="multilanguage" ignore="en">
  <ENTRY id="ActionText.Description.AI_ConfigureChainer">
    <STRING lang="en" value="ActionText.Description.AI_ConfigureChainer"/>
    <STRING lang="da" value=""/>
    <STRING lang="nl" value=""/>
    <STRING lang="fi" value=""/>
  </ENTRY>
</DICTIONARY>
`)

    err := xml.Unmarshal(b, &dict)
    if err != nil { panic(err) }

    fmt.Println(dict) // prints: {{ DICTIONARY}   []}

    dict.ignore = "test"

    out, err := xml.MarshalIndent(&dict, "  ", "    ")
    fmt.Println(string(out)) // prints:   <DICTIONARY></DICTIONARY>

    // huh?

}

回答1:

You need to Export (Capitalize) your struct fields.

From the encoding/xml Marshall function docs:

The XML element for a struct contains marshalled elements for each of the exported fields of the struct

See Unable to parse a complex json in golang for a related answer.