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XML 读取器和编写器----从流读取 XML

2006-12-06 19:01 211 查看

如何从流读取 XML 数据

此示例阐释如何使用 XmlTextReader 类从流读取 XML。流可能来自不同的源，如来自服务器、文件或 TextReader 的字节流。
注意：此示例是如何从文件读取 XML主题的继续。

VB ReadXmlStream.aspx

XmlTextReader 有不同的构造函数，以指定 XML 数据的位置。此示例从流加载 XmlTextReader。流是作为数据（在这里是指 XML 数据）的源或目标的输入或输出设备的抽象表示形式。您可以写入流或读取流，流的最形象化表示是字节流。流可提供不依赖于设备的独立性，因此，如果当流的源更改时，它不要求程序也进行更改。
下列示例代码创建 StringReader 类，它可构成 XML 字符串。由于该字符串是保留在内存中的纯字节流，您可以使用 XmlTextReader 将此字节流作为 XML 进行分析。此内存流没有特别指定的编码。然后，该示例创建一个 XmlTextReader，分析该流并显示所得到的 XML。

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td.code {
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border-style:solid;
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}
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text-align:center;
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td.space {
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border-bottom:0;
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border-color:cccccc;
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}

StringReader stream;
XmlTextReader reader = null;
try
{
Console.WriteLine ("Initializing StringReader ...");
stream = new StringReader("<?xml version='1.0'?>" +
"<!-- This file represents a fragment of a book store inventory database -->" +
"<bookstore>" +
" <book genre=\"autobiography\" publicationdate=\"1981\" ISBN=\"1-861003-11-0\">" +
"   <title>The Autobiography of Benjamin Franklin</title>" +
"   <author>" +
"       <first-name>Benjamin</first-name>" +
"       <last-name>Franklin</last-name>" +
"   </author>" +
"   <price>8.99</price>" +
" </book>" +
" <book genre=\"novel\" publicationdate=\"1967\" ISBN=\"0-201-63361-2\">" +
"   <title>The Confidence Man</title>" +
"   <author>" +
"       <first-name>Herman</first-name>" +
"       <last-name>Melville</last-name>" +
"   </author>" +
"   <price>11.99</price>" +
" </book>" +
"  <book genre=\"philosophy\" publicationdate=\"1991\" ISBN=\"1-861001-57-6\">" +
"   <title>The Gorgias</title>" +
"   <author>" +
"       <name>Plato</name>" +
"   </author>" +
"   <price>9.99</price>" +
" </book>" +
"</bookstore>");
// Load the XmlTextReader from the stream
reader = new XmlTextReader (stream);
Console.WriteLine ("Processing ...");
Console.WriteLine ();
FormatXml(reader);
}
catch (Exception e)
{
Console.WriteLine ("Exception: {0}", e.ToString());
}
finally
{
Console.WriteLine();
Console.WriteLine("Processing of stream complete.");
// Finished with XmlTextReader
if (reader != null)
reader.Close();
}

Dim stream as StringReader
Dim reader as XmlTextReader = nothing
try
Console.WriteLine ("Initializing StringReader ...")
stream = new StringReader ("<?xml version='1.0'?>" & _
"<!-- This file represents a fragment of a book store inventory database -->" & _
"<bookstore>" & _
" <book genre=""autobiography"" publicationdate=""1981"" ISBN=""1-861003-11-0"">" & _
"   <title>The Autobiography of Benjamin Franklin</title>" & _
"   <author>" & _
"       <first-name>Benjamin</first-name>" & _
"       <last-name>Franklin</last-name>" & _
"   </author>" & _
"   <price>8.99</price>" & _
" </book>" & _
" <book genre=""novel"" publicationdate=""1967"" ISBN=""0-201-63361-2"">" & _
"   <title>The Confidence Man</title>" & _
"   <author>" & _
"       <first-name>Herman</first-name>" & _
"       <last-name>Melville</last-name>" & _
"   </author>" & _
"   <price>11.99</price>" & _
" </book>" & _
"  <book genre=""philosophy"" publicationdate=""1991"" ISBN=""1-861001-57-6"">" & _
"   <title>The Gorgias</title>" & _
"   <author>" & _
"       <name>Plato</name>" & _
"   </author>" & _
"   <price>9.99</price>" & _
" </book>" & _
"</bookstore>")
' Load the XmlTextReader from the stream
reader = new XmlTextReader (stream)
Console.WriteLine ("Processing ...")
Console.WriteLine ()
FormatXml(reader)
catch e as Exception
Console.WriteLine ("Exception: {0} ", e.ToString())
finally
Console.WriteLine()
Console.WriteLine("Processing of stream complete.")
If Not reader Is Nothing
reader.Close()
end if
end try

如果流是作为输入提供的，则 XmlTextReader 属性将对它进行解码，方法是将该流包括在 StreamReader 中，然后根据指定的 XML 编码调用 SwitchEncoding 属性。另外，XmlResolver 用于解析正确分析输入所需的外部资源，如文档类型定义 (DTD) 和架构。表示流的另一种方法是通过使用 StreamReader 类，该类实现读取字符流的读取器。下列代码示例说明加载名为 books.xml 的文件，然后使用 XmlTextReader 分析结果文件。

StreamReader streamreader = new StreamReader ("books.xml");
Console.WriteLine ("File books.xml read sucessfully ...");
// Load the XmlTextReader from the StreamReader
XmlTextReader xmlreader = new XmlTextReader (streamreader);

Dim streamreader As StreamReader = New StreamReader ("books.xml")
Console.WriteLine ("File books.xml read sucessfully ...")
' Load the XmlTextReader from the StreamReader
Dim xmlreader As XmlTextReader = New XmlTextReader (streamreader)

此示例中的 FormalXml 方法显示在当前节点是元素节点的情况下，如何使用 MoveToNextAttribute 方法移到属性节点。这使您不但可以访问该节点的名称和值属性，而且由于此时处于节点上下文中，您还可以获取某些属性，如属性当前的命名空间。下列代码示例还显示 Format 方法，该方法此时显示当前节点的名称和值。

private static void FormatXml (XmlReader reader)
{
int piCount=0, docCount=0, commentCount=0, elementCount=0, attributeCount=0, textCount=0, whitespaceCount=0;
while (reader.Read())
{
switch (reader.NodeType)
{
case XmlNodeType.ProcessingInstruction:
Format (reader, "ProcessingInstruction");
piCount++;
break;
case XmlNodeType.DocumentType:
Format (reader, "DocumentType");
docCount++;
break;
case XmlNodeType.Comment:
Format (reader, "Comment");
commentCount++;
break;
case XmlNodeType.Element:
Format (reader, "Element");
while(reader.MoveToNextAttribute())
{
Format (reader, "Attribute");
}
elementCount++;
if (reader.HasAttributes)
attributeCount += reader.AttributeCount;
break;
case XmlNodeType.Text:
Format (reader, "Text");
textCount++;
break;
case XmlNodeType.Whitespace:
whitespaceCount++;
break;
}
}
// Display the Statistics
Console.WriteLine ();
Console.WriteLine("Statistics for stream");
Console.WriteLine ();
Console.WriteLine("ProcessingInstruction: {0}",piCount++);
Console.WriteLine("DocumentType: {0}",docCount++);
Console.WriteLine("Comment: {0}",commentCount++);
Console.WriteLine("Element: {0}",elementCount++);
Console.WriteLine("Attribute: {0}",attributeCount++);
Console.WriteLine("Text: {0}",textCount++);
Console.WriteLine("Whitespace: {0}",whitespaceCount++);
}
// Format the output
private static void Format(XmlReader reader, String nodeType)
{
// Format the output
Console.Write(reader.Depth + " ");
Console.Write(reader.AttributeCount + " ");
for (int i=0; i < reader.Depth; i++)
{
Console.Write('\t');
}
Console.Write(nodeType + "<" + reader.Name + ">" + reader.Value);
Console.WriteLine();
}

private shared sub FormatXml (reader as XmlTextReader)
Dim piCount, docCount, commentCount, elementCount as Integer
Dim attributeCount, textCount, whitespaceCount as Integer
While reader.Read()
Select (reader.NodeType)
case XmlNodeType.ProcessingInstruction:
Format (reader, "ProcessingInstruction")
piCount += 1
case XmlNodeType.DocumentType:
Format (reader, "DocumentType")
docCount += 1
case XmlNodeType.Comment:
Format (reader, "Comment")
commentCount += 1
case XmlNodeType.Element:
Format (reader, "Element")
elementCount += 1
While reader.MoveToNextAttribute()
Format (reader, "Attribute")
end While
if (reader.HasAttributes)
attributeCount += reader.AttributeCount
end if
case XmlNodeType.Text:
Format (reader, "Text")
textCount += 1
case XmlNodeType.Whitespace:
whitespaceCount += 1
end Select
end While
' Display the Statistics for the file
Console.WriteLine ()
Console.WriteLine("Statistics for stream")
Console.WriteLine ()
Console.WriteLine("ProcessingInstruction: " & piCount)
Console.WriteLine("DocumentType: " & docCount)
Console.WriteLine("Comment: " & commentCount)
Console.WriteLine("Element: " & elementCount)
Console.WriteLine("Attribute: " & attributeCount)
Console.WriteLine("Text: " & textCount)
Console.WriteLine("Whitespace: " & whitespaceCount)
end sub
private shared sub Format(byref reader as XmlTextReader, nodeType as String)
' Format the output
Console.Write(reader.Depth & " ")
Console.Write(reader.AttributeCount & " ")
Dim i as Integer
for i = 0 to reader.Depth
Console.Write(Strings.chr(9))
Next
Console.Write(reader.Prefix & nodeType & "<" & reader.Name & ">" & reader.Value)
Console.WriteLine()
end sub

摘要

流是作为数据的源或目标的输入或输出设备的抽象表示形式。
XmlTextReader 提供一些构造函数，用于从表示 URL 的字符串读取 XML，或从本地文件名、流或 TextReader 读取 XML。
XmlTextReader 提供从文件名、流或 TextReader 读取 XML 的构造函数。
可使用 MoveToNextAttribute 方法访问属性节点，该方法使您可以确定属性节点的属性

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