在 Web 服务消息中发送大数据集时会出现下面两个问题：
大的工作集（内存），由于序列化引擎的缓冲处理。
不正常的带宽占用，由于进行 Base64 编码后增大了 33%。
要解决这些问题，应实现 IXmlSerializable 接口，以控制序列化和反序列化。尤其是应实现 WriteXml 和 ReadXml 方法，以块化数据。
实现服务器端块化
在服务器计算机上，Web 方法必须关闭 ASP.NET 缓冲处理并返回实现 IXmlSerializable 的类型。
实现 IXmlSerializable 的类型在 WriteXml 方法中将数据块化。
实现客户端处理
将客户端代理上的 Web 方法更改为返回实现 IXmlSerializable 的类型。可以使用 SchemaImporterExtension 自动执行此更改，但是此处并未说明这种方法。
实现 ReadXml 方法，以读取块化数据流并将字节写入磁盘。此实现还会引发进度事件供图形控件（例如进度栏）使用。
示例
以下代码示例显示客户端上关闭了 ASP.NET 缓冲处理的 Web 方法。还显示客户端上 IXmlSerializable 接口的实现，该接口在 WriteXml 方法中将数据块化。
<WebMethod(), System.Web.Services.Protocols.SoapDocumentMethodAttribute(ParameterStyle := SoapParameterStyle.Bare)> _
Public Function DownloadSong(ByVal Authorization As DownloadAuthorization, ByVal filePath As String) As SongStream
' Turn off response buffering.
System.Web.HttpContext.Current.Response.Buffer = False
' Return a song.
Dim song As New SongStream(filePath)
Return song
End Function
...
<XmlSchemaProvider("MySchema")> _
Public Class SongStream
Implements IXmlSerializable
Private Const ns As String = "http://demos.Contoso.com/webservices"
Private filePath As String
Public Sub New()
End Sub
Public Sub New(ByVal filePath As String)
Me.filePath = filePath
End Sub
' This is the method named by the XmlSchemaProviderAttribute applied to the type.
Public Shared Function MySchema(ByVal xs As XmlSchemaSet) As XmlQualifiedName
' This method is called by the framework to get the schema for this type.
' We return an existing schema from disk.
Dim schemaSerializer As New XmlSerializer(GetType(XmlSchema))
Dim xsdPath As String = Nothing
' NOTE: replace SongStream.xsd with your own schema file.
xsdPath = System.Web.HttpContext.Current.Server.MapPath("SongStream.xsd")
Dim s As XmlSchema = CType(schemaSerializer.Deserialize(New XmlTextReader(xsdPath)), XmlSchema)
xs.XmlResolver = New XmlUrlResolver()
xs.Add(s)
Return New XmlQualifiedName("songStream", ns)
End Function
Sub WriteXml(ByVal writer As System.Xml.XmlWriter) Implements IXmlSerializable.WriteXml
' This is the chunking code.
' ASP.NET buffering must be turned off for this to work.
Dim bufferSize As Integer = 4096
Dim songBytes(bufferSize) As Char
Dim inFile As FileStream = File.Open(Me.filePath, FileMode.Open, FileAccess.Read)
Dim length As Long = inFile.Length
' Write the file name.
writer.WriteElementString("fileName", ns, Path.GetFileNameWithoutExtension(Me.filePath))
' Write the size.
writer.WriteElementString("size", ns, length.ToString())
' Write the song bytes.
writer.WriteStartElement("song", ns)
Dim sr As New StreamReader(inFile, True)
Dim readLen As Integer = sr.Read(songBytes, 0, bufferSize)
While readLen > 0
writer.WriteStartElement("chunk", ns)
writer.WriteChars(songBytes, 0, readLen)
writer.WriteEndElement()
writer.Flush()
readLen = sr.Read(songBytes, 0, bufferSize)
End While
writer.WriteEndElement()
inFile.Close()
End Sub
Function GetSchema() As System.Xml.Schema.XmlSchema Implements IXmlSerializable.GetSchema
Throw New System.NotImplementedException()
End Function
Sub ReadXml(ByVal reader As System.Xml.XmlReader) Implements IXmlSerializable.ReadXml
Throw New System.NotImplementedException()
End Sub
End Class
...
Public Class SongFile
Implements IXmlSerializable
Public Shared Event OnProgress As ProgressMade
Public Sub New()
End Sub
Private Const ns As String = "http://demos.teched2004.com/webservices"
Public Shared MusicPath As String
Private filePath As String
Private size As Double
Sub ReadXml(ByVal reader As System.Xml.XmlReader) Implements IXmlSerializable.ReadXml
reader.ReadStartElement("DownloadSongResult", ns)
ReadFileName(reader)
ReadSongSize(reader)
ReadAndSaveSong(reader)
reader.ReadEndElement()
End Sub
Sub ReadFileName(ByVal reader As XmlReader)
Dim fileName As String = reader.ReadElementString("fileName", ns)
Me.filePath = Path.Combine(MusicPath, Path.ChangeExtension(fileName, ".mp3"))
End Sub
Sub ReadSongSize(ByVal reader As XmlReader)
Me.size = Convert.ToDouble(reader.ReadElementString("size", ns))
End Sub
Sub ReadAndSaveSong(ByVal reader As XmlReader)
Dim outFile As FileStream = File.Open(Me.filePath, FileMode.Create, FileAccess.Write)
Dim songBase64 As String
Dim songBytes() As Byte
reader.ReadStartElement("song", ns)
Dim totalRead As Double = 0
While True
If reader.IsStartElement("chunk", ns) Then
songBase64 = reader.ReadElementString()
totalRead += songBase64.Length
songBytes = Convert.FromBase64String(songBase64)
outFile.Write(songBytes, 0, songBytes.Length)
outFile.Flush()
RaiseEvent OnProgress((100 *(totalRead / size)))
Else
Exit While
End If
End While
outFile.Close()
reader.ReadEndElement()
End Sub
<PermissionSet(SecurityAction.Demand, Name :="FullTrust")> _
Public Sub Play()
System.Diagnostics.Process.Start(Me.filePath)
End Sub
Function GetSchema() As System.Xml.Schema.XmlSchema Implements IXmlSerializable.GetSchema
Throw New System.NotImplementedException()
End Function
Public Sub WriteXml(ByVal writer As XmlWriter) Implements IXmlSerializable.WriteXml
Throw New System.NotImplementedException()
End Sub
End Class
[WebMethod]
[System.Web.Services.Protocols.SoapDocumentMethodAttribute
(ParameterStyle= SoapParameterStyle.Bare)]
public SongStream DownloadSong(DownloadAuthorization Authorization, string filePath)
{
// Turn off response buffering.
System.Web.HttpContext.Current.Response.Buffer = false;
// Return a song.
SongStream song = new SongStream(filePath);
return song;
}
...
[XmlSchemaProvider("MySchema")]
public class SongStream : IXmlSerializable
{
private const string ns = "http://demos.Contoso.com/webservices";
private string filePath;
public SongStream(){ }
public SongStream(string filePath)
{
this.filePath = filePath;
}
// This is the method named by the XmlSchemaProviderAttribute applied to the type.
public static XmlQualifiedName MySchema(XmlSchemaSet xs)
{
// This method is called by the framework to get the schema for this type.
// We return an existing schema from disk.
XmlSerializer schemaSerializer = new XmlSerializer(typeof(XmlSchema));
string xsdPath = null;
// NOTE: replace the string with your own path.
xsdPath = System.Web.HttpContext.Current.Server.MapPath("SongStream.xsd");
XmlSchema s = (XmlSchema)schemaSerializer.Deserialize(
new XmlTextReader(xsdPath), null);
xs.XmlResolver = new XmlUrlResolver();
xs.Add(s);
return new XmlQualifiedName("songStream", ns);
}
void IXmlSerializable.WriteXml(System.Xml.XmlWriter writer)
{
// This is the chunking code.
// ASP.NET buffering must be turned off for this to work.
int bufferSize = 4096;
char[] songBytes = new char[bufferSize];
FileStream inFile = File.Open(this.filePath, FileMode.Open, FileAccess.Read);
long length = inFile.Length;
// Write the file name.
writer.WriteElementString("fileName", ns, Path.GetFileNameWithoutExtension(this.filePath));
// Write the size.
writer.WriteElementString("size", ns, length.ToString());
// Write the song bytes.
writer.WriteStartElement("song", ns);
StreamReader sr = new StreamReader(inFile, true);
int readLen = sr.Read(songBytes, 0, bufferSize);
while (readLen > 0)
{
writer.WriteStartElement("chunk", ns);
writer.WriteChars(songBytes, 0, readLen);
writer.WriteEndElement();
writer.Flush();
readLen = sr.Read(songBytes, 0, bufferSize);
}
writer.WriteEndElement();
inFile.Close();
}
System.Xml.Schema.XmlSchema IXmlSerializable.GetSchema()
{
throw new System.NotImplementedException();
}
void IXmlSerializable.ReadXml(System.Xml.XmlReader reader)
{
throw new System.NotImplementedException();
}
}
...
public class SongFile : IXmlSerializable
{
public static event ProgressMade OnProgress;
public SongFile()
{ }
private const string ns = "http://demos.teched2004.com/webservices";
public static string MusicPath;
private string filePath;
private double size;
void IXmlSerializable.ReadXml(System.Xml.XmlReader reader)
{
reader.ReadStartElement("DownloadSongResult", ns);
ReadFileName(reader);
ReadSongSize(reader);
ReadAndSaveSong(reader);
reader.ReadEndElement();
}
void ReadFileName(XmlReader reader)
{
string fileName = reader.ReadElementString("fileName", ns);
this.filePath =
Path.Combine(MusicPath, Path.ChangeExtension(fileName, ".mp3"));
}
void ReadSongSize(XmlReader reader)
{
this.size = Convert.ToDouble(reader.ReadElementString("size", ns));
}
void ReadAndSaveSong(XmlReader reader)
{
FileStream outFile = File.Open(
this.filePath, FileMode.Create, FileAccess.Write);
string songBase64;
byte[] songBytes;
reader.ReadStartElement("song", ns);
double totalRead=0;
while(true)
{
if (reader.IsStartElement("chunk", ns))
{
songBase64 = reader.ReadElementString();
totalRead += songBase64.Length;
songBytes = Convert.FromBase64String(songBase64);
outFile.Write(songBytes, 0, songBytes.Length);
outFile.Flush();
if (OnProgress != null)
{
OnProgress(100 * (totalRead / size));
}
}
else
{
break;
}
}
outFile.Close();
reader.ReadEndElement();
}
[PermissionSet(SecurityAction.Demand, Name="FullTrust")]
public void Play()
{
System.Diagnostics.Process.Start(this.filePath);
}
System.Xml.Schema.XmlSchema IXmlSerializable.GetSchema()
{
throw new System.NotImplementedException();
}
public void WriteXml(XmlWriter writer)
{
throw new System.NotImplementedException();
}
}
编译代码
- 代码使用下列命名空间：System、System.Runtime.Serialization、System.Web.Services、System.Web.Services.Protocols、System.Xml、System.Xml.Serialization 和 System.Xml.Schema。