如何：區塊序列化資料
警告
使用 BinaryFormatter 進行二進位序列化可能很危險。 如需詳細資訊，請參閱 BinaryFormatter 安全性指南。
在 Web 服務訊息中發送大型資料集時發生的兩項問題為：
由於序列化引擎緩衝而產生的大型工作集 (記憶體)。
由於 Base64 編碼後暴增 33%，因此過度消耗頻寬。
若要解決這些問題，請實作 IXmlSerializable 介面以控制序列化與還原序列化。 具體地說，實作 WriteXml 和 ReadXml 方法將資料區分成區塊。
實作伺服器端區分區塊的功能
在伺服器機器上，Web 方法必須關閉 ASP.NET 緩衝並傳回實作 IXmlSerializable的型別。
實作 IXmlSerializable 的型別會將 WriteXml 方法中的資料區分區塊。
實作用戶端處理
變更用戶端 Proxy 上的 Web 方法以傳回實作 IXmlSerializable的型別。 您可以使用 SchemaImporterExtension 自動執行這個作業，不過在此不予以討論。
實作 ReadXml 方法讀取區分成區塊的資料流並將位元組寫入磁碟。 此實作也引發圖形控制項可使用的進度事件，例如進度列。
範例
下列程式碼範例顯示關閉 ASP.NET 緩衝之用戶端上的 Web 方法。 它也顯示用戶端 IXmlSerializable 介面的實作，將 WriteXml 方法中的資料區分區塊。
[WebMethod]
[SoapDocumentMethod(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;
}
<WebMethod(), 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
End Class
[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();
}
XmlSchema IXmlSerializable.GetSchema()
{
throw new NotImplementedException();
}
void IXmlSerializable.ReadXml(System.Xml.XmlReader reader)
{
throw new NotImplementedException();
}
}
<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 : 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();
}
public void Play()
{
System.Diagnostics.Process.Start(this.filePath);
}
XmlSchema IXmlSerializable.GetSchema()
{
throw new NotImplementedException();
}
public void WriteXml(XmlWriter writer)
{
throw new NotImplementedException();
}
}
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
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
編譯程式碼
- 程式碼使用下列命名空間：System、System.Runtime.Serialization、System.Web.Services、System.Web.Services.Protocols、System.Xml、System.Xml.Serialization 和 System.Xml.Schema。
另請參閱
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