Cómo: Exponer una fuente como Atom y RSS

Artículo
02/27/2011

Windows Communication Foundation (WCF) le permite crear un servicio que exponga una fuente de distribución. En este tema se explica cómo crear un servicio de distribución que exponga una fuente de distribución mediante Atom 1.0 y RSS 2.0. Este servicio expone un extremo que puede devolver cualquiera de los dos formatos de distribución. Para simplificar, el servicio usado en este ejemplo tiene host propio. En un entorno de producción, un servicio de este tipo se hospedaría en IIS o WAS. Para obtener más información sobre las distintas opciones de hospedaje de WCF, vea Hospedaje.

Creación de un servicio de distribución básico

Defina un contrato de servicios utilizando una interfaz marcada con el atributo WebGetAttribute. Cada operación que se expone como una fuente de distribución devuelve un objeto SyndicationFeedFormatter. Tenga en cuenta los parámetros del WebGetAttribute. UriTemplate especifica la URL utilizada para invocar esta operación de servicio. La cadena de este parámetro contiene literales y una variable entre llaves ({format}). Esta variable corresponde al parámetro format de la operación del servicio. Para obtener más información, vea UriTemplate. BodyStyle afecta a la forma en la que se escriben los mensajes que esta operación de servicio envía y recibe. Bare especifica que los datos enviados a y desde esta operación de servicio no están contenidos en elementos XML definidos por la infraestructura. Para obtener más información, vea WebMessageBodyStyle.
```
<ServiceContract()> _
<ServiceKnownType(GetType(Atom10FeedFormatter))> _
<ServiceKnownType(GetType(Rss20FeedFormatter))> _
Public Interface IBlog
    <OperationContract()> _
    <WebGet(UriTemplate:="GetBlog?format={format}")> _
    Function GetBlog(ByVal format As String) As SyndicationFeedFormatter
End Interface
```
```
[ServiceContract]
[ServiceKnownType(typeof(Atom10FeedFormatter))]
[ServiceKnownType(typeof(Rss20FeedFormatter))]
public interface IBlog
{
    [OperationContract]
    [WebGet(UriTemplate = "GetBlog?format={format}")]
    SyndicationFeedFormatter GetBlog(string format);
}
```
Nota:

Utilice el ServiceKnownTypeAttribute para especificar los tipos que devuelven las operaciones de servicio en esta interfaz.

Nota:
Utilice el ServiceKnownTypeAttribute para especificar los tipos que devuelven las operaciones de servicio en esta interfaz.

Implemente el contrato de servicios.

Public Class BlogService
    implements IBlog

    Public Function GetBlog(ByVal format As String) As SyndicationFeedFormatter Implements IBlog.GetBlog
        Dim feed As New SyndicationFeed("My Blog Feed", "This is a test feed", New Uri("http://SomeURI"))
        feed.Authors.Add(New SyndicationPerson("someone@microsoft.com"))
        feed.Categories.Add(New SyndicationCategory("How To Sample Code"))
        feed.Description = New TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF")
        Dim item1 As New SyndicationItem( _
            "Item One", _
            "This is the content for item one", _
            New Uri("https://localhost/Content/One"), _
            "ItemOneID", _
            DateTime.Now)

        Dim item2 As New SyndicationItem( _
            "Item Two", _
            "This is the content for item two", _
            New Uri("https://localhost/Content/Two"), _
            "ItemTwoID", _
            DateTime.Now)

        Dim item3 As New SyndicationItem( _
            "Item Three", _
            "This is the content for item three", _
            New Uri("https://localhost/Content/three"), _
            "ItemThreeID", _
            DateTime.Now)
        Dim items As New List(Of SyndicationItem)()
        items.Add(item1)
        items.Add(item2)
        items.Add(item3)

        feed.Items = items

        If (format = "rss") Then
            Return New Rss20FeedFormatter(feed)
        Else
            Return New Atom10FeedFormatter(feed)
        End If
    End Function
End Class

public class BlogService : IBlog
{
    public SyndicationFeedFormatter GetBlog(string format)
    {
        SyndicationFeed feed = new SyndicationFeed("My Blog Feed", "This is a test feed", new Uri("http://SomeURI"));
        feed.Authors.Add(new SyndicationPerson("someone@microsoft.com"));
        feed.Categories.Add(new SyndicationCategory("How To Sample Code"));
        feed.Description = new TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF");
        SyndicationItem item1 = new SyndicationItem(
            "Item One",
            "This is the content for item one",
            new Uri("https://localhost/Content/One"),
            "ItemOneID",
            DateTime.Now);

        SyndicationItem item2 = new SyndicationItem(
            "Item Two",
            "This is the content for item two",
            new Uri("https://localhost/Content/Two"),
            "ItemTwoID",
            DateTime.Now);

        SyndicationItem item3 = new SyndicationItem(
            "Item Three",
            "This is the content for item three",
            new Uri("https://localhost/Content/three"),
            "ItemThreeID",
            DateTime.Now);
        List<SyndicationItem> items = new List<SyndicationItem>();
        items.Add(item1);
        items.Add(item2);
        items.Add(item3);

        feed.Items = items;

        if (format == "rss")
            return new Rss20FeedFormatter(feed);
        else if (format == "atom")
            return new Atom10FeedFormatter(feed);
        else return null;
    }
}

Cree un objeto SyndicationFeed y agregue un autor, categoría y descripción.

Dim feed As New SyndicationFeed("My Blog Feed", "This is a test feed", New Uri("http://SomeURI"))
feed.Authors.Add(New SyndicationPerson("someone@microsoft.com"))
feed.Categories.Add(New SyndicationCategory("How To Sample Code"))
feed.Description = New TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF")

SyndicationFeed feed = new SyndicationFeed("My Blog Feed", "This is a test feed", new Uri("http://SomeURI"));
feed.Authors.Add(new SyndicationPerson("someone@microsoft.com"));
feed.Categories.Add(new SyndicationCategory("How To Sample Code"));
feed.Description = new TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF");

Cree varios objetos SyndicationItem.

Dim item1 As New SyndicationItem( _
    "Item One", _
    "This is the content for item one", _
    New Uri("https://localhost/Content/One"), _
    "ItemOneID", _
    DateTime.Now)

Dim item2 As New SyndicationItem( _
    "Item Two", _
    "This is the content for item two", _
    New Uri("https://localhost/Content/Two"), _
    "ItemTwoID", _
    DateTime.Now)

Dim item3 As New SyndicationItem( _
    "Item Three", _
    "This is the content for item three", _
    New Uri("https://localhost/Content/three"), _
    "ItemThreeID", _
    DateTime.Now)

SyndicationItem item1 = new SyndicationItem(
    "Item One",
    "This is the content for item one",
    new Uri("https://localhost/Content/One"),
    "ItemOneID",
    DateTime.Now);

SyndicationItem item2 = new SyndicationItem(
    "Item Two",
    "This is the content for item two",
    new Uri("https://localhost/Content/Two"),
    "ItemTwoID",
    DateTime.Now);

SyndicationItem item3 = new SyndicationItem(
    "Item Three",
    "This is the content for item three",
    new Uri("https://localhost/Content/three"),
    "ItemThreeID",
    DateTime.Now);

Agregue los objetos SyndicationItem a la fuente.

Dim items As New List(Of SyndicationItem)()
items.Add(item1)
items.Add(item2)
items.Add(item3)

feed.Items = items

List<SyndicationItem> items = new List<SyndicationItem>();
items.Add(item1);
items.Add(item2);
items.Add(item3);

feed.Items = items;

Utilice el parámetro format para devolver el formato solicitado.

If (format = "rss") Then
    Return New Rss20FeedFormatter(feed)
Else
    Return New Atom10FeedFormatter(feed)
End If

if (format == "rss")
    return new Rss20FeedFormatter(feed);
else if (format == "atom")
    return new Atom10FeedFormatter(feed);
else return null;

Para hospedar el servicio

Cree un objeto WebServiceHost. La clase WebServiceHost agrega automáticamente un extremo en la dirección base del servicio, salvo que se especifique uno en el código o en la configuración. En este ejemplo, no se especifica ningún extremo, por lo que se expone el predeterminado.
```
Dim address As New Uri("https://localhost:8000/BlogService/")
Dim svcHost As New WebServiceHost(GetType(BlogService), address)
```
```
Uri address = new Uri("https://localhost:8000/BlogService/");
WebServiceHost svcHost = new WebServiceHost(typeof(BlogService), address);
```

Abra el host del servicio, cargue la fuente desde el servicio, muestre la fuente y espere a que el usuario presione Entrar.

svcHost.Open()
Console.WriteLine("Service is running")

Console.WriteLine("Loading feed in Atom 1.0 format.")
Dim atomReader As XmlReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=atom")
Dim atomFeed As SyndicationFeed = SyndicationFeed.Load(atomReader)
Console.WriteLine(atomFeed.Title.Text)
Console.WriteLine("Items:")
For Each item As SyndicationItem In atomFeed.Items
    Console.WriteLine("Title: {0}", item.Title.Text)
    Console.WriteLine("Content: {0}", CType(item.Content, TextSyndicationContent).Text)
Next

Console.WriteLine("Loading feed in RSS 2.0 format.")
Dim rssReader As XmlReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=rss")
Dim rssFeed As SyndicationFeed = SyndicationFeed.Load(rssReader)
Console.WriteLine(rssFeed.Title.Text)
Console.WriteLine("Items:")
For Each item As SyndicationItem In rssFeed.Items
    Console.WriteLine("Title: {0}", item.Title.Text)
    Console.WriteLine("Content: {0}", CType(item.Content, TextSyndicationContent).Text)
Next


Console.WriteLine("Press <ENTER> to quit...")
Console.ReadLine()
svcHost.Close()

svcHost.Open();
Console.WriteLine("Service is running");

Console.WriteLine("Loading feed in Atom 1.0 format.");
XmlReader atomReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=atom");
SyndicationFeed atomFeed = SyndicationFeed.Load(atomReader);
Console.WriteLine(atomFeed.Title.Text);
Console.WriteLine("Items:");
foreach (SyndicationItem item in atomFeed.Items)
{
    Console.WriteLine("Title: {0}", item.Title.Text);
    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Content).Text);
}

Console.WriteLine("Loading feed in RSS 2.0 format.");
XmlReader rssReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=rss");
SyndicationFeed rssFeed = SyndicationFeed.Load(rssReader);
Console.WriteLine(rssFeed.Title.Text);
Console.WriteLine("Items:");
foreach (SyndicationItem item in rssFeed.Items)
{
    Console.WriteLine("Title: {0}", item.Title.Text);
    // Notice we are using item.Summary here instead of item.Content. This is because
    // of the differences between Atom 1.0 and RSS 2.0 specs.
    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Summary).Text);
}

Console.WriteLine("Press <ENTER> to quit...");
Console.ReadLine();
svcHost.Close();

Llamar a GetBlog mediante HTTP GET

Abra Internet Explorer, escriba la siguiente URL y presione Entrar. https://localhost:8000/BlogService/GetBlog

La URL contiene la dirección base del servicio (https://localhost:8000/BlogService), la dirección relativa del extremo y la operación del servicio que se va a llamar.

Llamar a GetBlog() mediante código

Cree un XmlReader con la dirección base y el método al que está llamando.

Dim atomReader As XmlReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=atom")

XmlReader reader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=atom");

Llame al método estático Load, pasando el XmlReader que acaba de crear.
```
Dim feed As SyndicationFeed = SyndicationFeed.Load(atomReader)
```
```
SyndicationFeed feed = SyndicationFeed.Load(reader);
```
Esto invoca la operación de servicio y rellena una nueva SyndicationFeed con el formateador devuelto desde la operación del servicio.

Obtenga acceso al objeto de fuente.

Console.WriteLine(feed.Title.Text)
Console.WriteLine("Items:")
For Each item As SyndicationItem In feed.Items
    Console.WriteLine("Title: {0}", item.Title.Text)
    Console.WriteLine("Content: {0}", (CType(item.Content, TextSyndicationContent).Text))
Next

Console.WriteLine(feed.Title.Text);
Console.WriteLine("Items:");
foreach (SyndicationItem item in feed.Items)
{
    Console.WriteLine("Title: {0}", item.Title.Text);
    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Content).Text);
}

Ejemplo

A continuación, se muestra una lista de código completa en este ejemplo.

using System;
using System.Xml;
using System.Collections.Generic;
using System.ServiceModel;
using System.ServiceModel.Description;
using System.ServiceModel.Syndication;
using System.ServiceModel.Web;
namespace Service
{
    [ServiceContract]
    [ServiceKnownType(typeof(Atom10FeedFormatter))]
    [ServiceKnownType(typeof(Rss20FeedFormatter))]
    public interface IBlog
    {
        [OperationContract]
        [WebGet(UriTemplate = "GetBlog?format={format}")]
        SyndicationFeedFormatter GetBlog(string format);
    }

    public class BlogService : IBlog
    {
        public SyndicationFeedFormatter GetBlog(string format)
        {
            SyndicationFeed feed = new SyndicationFeed("My Blog Feed", "This is a test feed", new Uri("http://SomeURI"));
            feed.Authors.Add(new SyndicationPerson("someone@microsoft.com"));
            feed.Categories.Add(new SyndicationCategory("How To Sample Code"));
            feed.Description = new TextSyndicationContent("This is a sample that demonstrates how to expose a feed through RSS and Atom with WCF");
            SyndicationItem item1 = new SyndicationItem(
                "Item One",
                "This is the content for item one",
                new Uri("https://localhost/Content/One"),
                "ItemOneID",
                DateTime.Now);

            SyndicationItem item2 = new SyndicationItem(
                "Item Two",
                "This is the content for item two",
                new Uri("https://localhost/Content/Two"),
                "ItemTwoID",
                DateTime.Now);

            SyndicationItem item3 = new SyndicationItem(
                "Item Three",
                "This is the content for item three",
                new Uri("https://localhost/Content/three"),
                "ItemThreeID",
                DateTime.Now);
            List<SyndicationItem> items = new List<SyndicationItem>();
            items.Add(item1);
            items.Add(item2);
            items.Add(item3);

            feed.Items = items;

            if (format == "rss")
                return new Rss20FeedFormatter(feed);
            else if (format == "atom")
                return new Atom10FeedFormatter(feed);
            else return null;
        }
    }

    public class Host
    {
        static void Main(string[] args)
        {
            Uri address = new Uri("https://localhost:8000/BlogService/");
            WebServiceHost svcHost = new WebServiceHost(typeof(BlogService), address);
            try
            {
                svcHost.Open();
                Console.WriteLine("Service is running");

                Console.WriteLine("Loading feed in Atom 1.0 format.");
                XmlReader atomReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=atom");
                SyndicationFeed atomFeed = SyndicationFeed.Load(atomReader);
                Console.WriteLine(atomFeed.Title.Text);
                Console.WriteLine("Items:");
                foreach (SyndicationItem item in atomFeed.Items)
                {
                    Console.WriteLine("Title: {0}", item.Title.Text);
                    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Content).Text);
                }

                Console.WriteLine("Loading feed in RSS 2.0 format.");
                XmlReader rssReader = XmlReader.Create("https://localhost:8000/BlogService/GetBlog?format=rss");
                SyndicationFeed rssFeed = SyndicationFeed.Load(rssReader);
                Console.WriteLine(rssFeed.Title.Text);
                Console.WriteLine("Items:");
                foreach (SyndicationItem item in rssFeed.Items)
                {
                    Console.WriteLine("Title: {0}", item.Title.Text);
                    // Notice we are using item.Summary here instead of item.Content. This is because
                    // of the differences between Atom 1.0 and RSS 2.0 specs.
                    Console.WriteLine("Content: {0}", ((TextSyndicationContent)item.Summary).Text);
                }

                Console.WriteLine("Press <ENTER> to quit...");
                Console.ReadLine();
                svcHost.Close();
            }
            catch (CommunicationException ce)
            {
                Console.WriteLine("An exception occurred: {0}", ce.Message);
                svcHost.Abort();
            }
        }
    }
}

Compilar el código

Al compilar el código anterior, haga referencia a System.ServiceModel.dll y System.ServiceModel.Web.dll.

Vea también

Referencia

WebHttpBinding
WebGetAttribute

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