VB.NET中如何从XML文件构建唯一树结构并统计节点属性

需求背景 #

需要从结构不明确的XML文件中生成节点与属性的唯一列表，统计每类节点/属性组合的出现次数。

示例输入XML #

<level1>
    <item id="a">blah</item>
    <item id="b">blah</item>
    <item id="c">blah</item>
    <level2>
        <item id="d">blah</item>
        <item id="e">blah</item>
        <item id="f">blah</item>
        <level3>
            <item id="g">blah</item>
            <item id="h">blah</item>
            <item id="i">blah</item>
            <item id="k">blah</item>
        </level3>
        <level3>
            <item id="g">blah</item>
            <item id="h">blah</item>
            <item id="i">blah</item>
            <item id="j">blah</item>
        </level3>
    </level2>
    <level2>
        <item id="d">blah</item>
        <item id="e">blah</item>
        <item id="f">blah</item>
        <item id="k">blah</item>
        <level3>
            <item id="g">blah</item>
            <item id="i">blah</item>
        </level3>
        <level3>
            <item id="g">blah</item>
            <item id="h">blah</item>
            <item id="j">blah</item>
        </level3>
    </level2>
</level1>

期望输出效果 #

<level1 count="1">
    <item id="a">1</item>
    <item id="b">1</item>
    <item id="c">1</item>
    <level2 count="2">
        <item id="d">2</item>
        <item id="e">2</item>
        <item id="f">2</item>
        <item id="k">1</item>
        <level3 count="4">
            <item id="g">4</item>
            <item id="h">3</item>
            <item id="i">3</item>
            <item id="j">2</item>
            <item id="k">1</item>
        </level3>
    </level2>
</level1>

现有开发条件 #

• 开发环境：VS2019 + VB.NET
• 已有基础遍历代码：

For Each Element As XmlElement In XmlDoc.SelectNodes("//*")
    Console.WriteLine("Processing element with name {0}:", Element.Name)
    
    For Each Attribute As XmlAttribute In Element.Attributes
        Console.WriteLine("{0}: {1}", Attribute.Name, Attribute.Value)
    Next

    Console.WriteLine()
Next

实现方案 #

1. 自定义数据存储结构 #

使用嵌套类存储每个节点的统计信息，天然匹配XML树状结构：

Public Class XmlNodeStat
    ' 节点名称
    Public Property Name As String
    ' 节点出现次数
    Public Property Count As Integer = 0
    ' 该节点下的属性值统计：Key为"属性名:属性值"，Value为出现次数
    Public Property AttributeCounts As New Dictionary(Of String, Integer)
    ' 子节点统计：Key为子节点名称，Value为子节点的统计对象
    Public Property ChildStats As New Dictionary(Of String, XmlNodeStat)
End Class

2. 统计逻辑实现 #

递归遍历XML节点，逐层累加计数：

' 根统计对象
Dim rootStat As New XmlNodeStat() With {.Name = "Root"}

' 入口调用：传入XML文档根节点、根统计对象
ProcessNode(XmlDoc.DocumentElement, rootStat)

' 递归处理节点的方法
Sub ProcessNode(node As XmlElement, parentStat As XmlNodeStat)
    ' 1. 累加当前节点计数
    If Not parentStat.ChildStats.ContainsKey(node.Name) Then
        parentStat.ChildStats(node.Name) = New XmlNodeStat() With {.Name = node.Name}
    End If
    Dim currentStat = parentStat.ChildStats(node.Name)
    currentStat.Count += 1

    ' 2. 累加属性值计数
    For Each attr As XmlAttribute In node.Attributes
        Dim attrKey = $"{attr.Name}:{attr.Value}"
        If Not currentStat.AttributeCounts.ContainsKey(attrKey) Then
            currentStat.AttributeCounts(attrKey) = 0
        End If
        currentStat.AttributeCounts(attrKey) += 1
    Next

    ' 3. 递归处理所有子元素节点
    For Each child As XmlElement In node.ChildNodes.OfType(Of XmlElement)()
        ProcessNode(child, currentStat)
    Next
End Sub

3. 结果输出示例 #

可以按需输出为XML或者文本格式，以下是生成类示例输出的方法：

Sub PrintStat(stat As XmlNodeStat, Optional indent As Integer = 0)
    Dim indentStr = New String(" "c, indent * 4)
    ' 输出节点本身统计
    Console.WriteLine($"{indentStr}<{stat.Name} count=""{stat.Count}"">")
    ' 输出属性统计
    For Each attr In stat.AttributeCounts
        Dim attrParts = attr.Key.Split(":"c)
        Console.WriteLine($"{indentStr}    <item {attrParts(0)}=""{attrParts(1)}"">{attr.Value}</item>")
    Next
    ' 输出子节点
    For Each child In stat.ChildStats.Values
        PrintStat(child, indent + 1)
    Next
    Console.WriteLine($"{indentStr}</{stat.Name}>")
End Sub

' 调用输出：
PrintStat(rootStat.ChildStats.Values.First()) ' 传入根节点统计对象

内容的提问来源于stack exchange，提问作者Paul Stearns