如何解析GO中忽略嵌套元素的巨大xml？

Question

I have this XML, for example:

     <Report>
        ...
        <ElementOne Blah="bleh">
            <IgnoreElement>
                <Foo>
                   ...
                </Foo>
            </IgnoreElement>

            <WantThisElement>
                <Bar Baz="test">
                   ...
                </Bar>
                <Bar Baz="test2">
                   ...
                </Bar>
            </WantThisElement>
        </ElementOne>
        ...
    </Report>

And I'm parsing this with encode/xml:

    ... 
    decoder := xml.NewDecoder(resp.Body)
    Mystruct := MyStruct{}
    for {
    t, _ := decoder.Token()

    if t == nil {
        break
    }
    switch se := t.(type) {
    case xml.StartElement:
        if se.Name.Local == "ElementOne" {
            decoder.DecodeElement(&Mystruct, &se)
        }
    }
    ...



   type MyStruct struct{
        Blah string
        Bar []Bar
   }
   type Bar struct{
        Baz string
        ...
   }

I'm not sure if it is the best way to do it and I don't know if the decoder.DecodeElement(...) ignoring the nested elements that I don't want to parse. I want to increase perfomance with low memory cost. What the best way to parser these huge XML files?

Answer 1

Typically it is best to use XML decoder for large XML, it uses the stream and Go with selective binding (like WantThisElement>Bar) then XML decoder follows that path.

Let's use XML content from your question to create an example.

XML Content:

<Report>
    <ElementOne Blah="bleh">
        <IgnoreElement>
            <Foo>
                <FooValue>example foo value</FooValue>
            </Foo>
        </IgnoreElement>

        <WantThisElement>
            <Bar Baz="test">
                 <BarValue>example bar value 1</BarValue>
            </Bar>
            <Bar Baz="test2">
                <BarValue>example bar value 2</BarValue>
            </Bar>
        </WantThisElement>
    </ElementOne>
</Report>

Structures:

type Report struct {
    XMLName    xml.Name `xml:"Report"`
    ElementOne ElementOne
}

type ElementOne struct {
    XMLName xml.Name `xml:"ElementOne"`
    Blah    string   `xml:"Blah,attr"`
    Bar     []Bar    `xml:"WantThisElement>Bar"`
}

type Bar struct {
    XMLName  xml.Name `xml:"Bar"`
    Baz      string   `xml:"Baz,attr"`
    BarValue string   `xml:"BarValue"`
}

Play Link: https://play.golang.org/p/26xDkojeUp