方法 : シリアル化されたデータをチャンクする
Web サービス メッセージ内で大容量データ セットを送信すると、次の 2 つの問題が発生します。
シリアル化エンジンのバッファリングによるワーキング セット (メモリ) の巨大化
Base64 エンコーディングの実行後はサイズが 33% 増加することによる、帯域幅の過度の消費
これらの問題を解決するには、シリアル化および逆シリアル化を制御する IXmlSerializable インターフェイスを実装します。特に、WriteXml および ReadXml を実装することで、データをチャンクします。
サーバー側チャンク処理を実装するには
サーバー コンピュータ上で、Web メソッドが ASP.NET バッファリングを無効にし、IXmlSerializable を実装する型を返す必要があります。
IXmlSerializable を実装する型は、WriteXml メソッド内でデータをチャンクします。
クライアント側の処理を実装するには
クライアント プロキシ上で、IXmlSerializable を実装する型を返すように Web メソッドを変更します。SchemaImporterExtension を使用するとこの処理を自動化できますが、この方法はここでは説明しません。
チャンクされたデータ ストリームを読み取り、バイトをディスクに書き込むための ReadXml メソッドを実装します。この実装により、進行状況イベントも発生します。これは、プログレス バーなどのグラフィック コントロールに使用できます。
使用例
次のコードは、クライアント上で ASP.NET バッファリングを無効にする Web メソッドの例を示します。また、WriteXml メソッドにおいてデータをチャンクする IXmlSerializable インターフェイスをクライアント側で実装する方法も示します。
<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();
}
}
コードのコンパイル方法
- このコードでは、System、System.Runtime.Serialization、System.Web.Services、System.Web.Services.Protocols、System.Xml、System.Xml.Serialization、および System.Xml.Schema の各名前空間が使用されています。