Como: fragmentar dados serializados

Dois problemas que ocorrem ao enviar grandes conjuntos de dados em mensagens de serviço Web são:

1. Um grande conjunto de trabalho (memória) devido ao buffer pelo mecanismo de serialização.

2. Consumo excessivo de largura de banda devido à inflação de 33% após a codificação Base64.

Para resolver esses problemas, implemente a IXmlSerializable interface para controlar a serialização e desserialização. Especificamente, implemente os WriteXml métodos e ReadXml para fragmentar os dados.

Para implementar o agrupamento do lado do servidor

1. Na máquina do servidor, o método Web deve desativar o buffer de ASP.NET e retornar um tipo que implementa IXmlSerializableo .

2. O tipo que implementa IXmlSerializable partes dos dados no WriteXml método.

Para implementar o processamento do lado do cliente

1. Altere o método Web no proxy do cliente para retornar o tipo que implementa IXmlSerializableo . Você pode usar um SchemaImporterExtension para fazer isso automaticamente, mas isso não é mostrado aqui.

2. Implemente o ReadXml método para ler o fluxo de dados em partes e gravar os bytes no disco. Essa implementação também gera eventos de progresso que podem ser usados por um controle gráfico, como uma barra de progresso.

Exemplo

O exemplo de código a seguir mostra o método Web no cliente que desativa o buffer ASP.NET. Ele também mostra a implementação do lado do cliente da IXmlSerializable interface que fragmenta os dados no WriteXml método.

[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

Compilação do código

• O código usa os seguintes namespaces: System, System.Runtime.Serialization, System.Web.Services, System.Web.Services.Protocols, System.Xml, System.Xml.Serializatione System.Xml.Schema.

Consulte também

• Serialização personalizada