Como: expor um feed como Atom e RSS

O WCF (Windows Communication Foundation) permite que você crie um serviço que expõe um feed de sindicalização. Este tópico discute como criar um serviço de sindicalização que expõe um feed de sindicalização usando o Atom 1.0 e o RSS 2.0. Esse serviço expõe um ponto de extremidade que pode retornar qualquer formato de sindicalização. Para simplificar, o serviço usado neste exemplo é auto-hospedado. Em um ambiente de produção, um serviço desse tipo seria hospedado em IIS ou WAS. Para obter mais informações sobre as diferentes opções de hospedagem do WCF, consulte Hospedagem.

Para criar um serviço de sindicalização básico

1. Defina um contrato de serviço usando uma interface marcada com o atributo WebGetAttribute. Cada operação exposta como um feed de sindicalização retorna um objeto SyndicationFeedFormatter. Observe os parâmetros para o WebGetAttribute. UriTemplate especifica a URL usada para invocar essa operação de serviço. A cadeia de caracteres para esse parâmetro contém literais e uma variável em chaves ({format}). Essa variável corresponde ao parâmetro format da operação de serviço. Para obter mais informações, consulte UriTemplate. BodyStyle afeta a forma como as mensagens enviadas e recebidas por essa operação de serviço são gravadas. Bare especifica que os dados enviados de e para essa operação de serviço não são encapsulados por elementos XML definidos pela infraestrutura. Para obter mais informações, consulte WebMessageBodyStyle.

   [ServiceContract]
   [ServiceKnownType(typeof(Atom10FeedFormatter))]
   [ServiceKnownType(typeof(Rss20FeedFormatter))]
   public interface IBlog
   {
       [OperationContract]
       [WebGet(UriTemplate = "GetBlog?format={format}")]
       SyndicationFeedFormatter GetBlog(string format);
   }
   

   <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
   

   Observação

   Use o ServiceKnownTypeAttribute para especificar os tipos que são retornados pelas operações de serviço nessa interface.

2. Implemente o contrato de serviço.

   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("http://localhost/Content/One"),
               "ItemOneID",
               DateTime.Now);
   
           SyndicationItem item2 = new SyndicationItem(
               "Item Two",
               "This is the content for item two",
               new Uri("http://localhost/Content/Two"),
               "ItemTwoID",
               DateTime.Now);
   
           SyndicationItem item3 = new SyndicationItem(
               "Item Three",
               "This is the content for item three",
               new Uri("http://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 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("http://localhost/Content/One"), _
               "ItemOneID", _
               DateTime.Now)
   
           Dim item2 As New SyndicationItem( _
               "Item Two", _
               "This is the content for item two", _
               New Uri("http://localhost/Content/Two"), _
               "ItemTwoID", _
               DateTime.Now)
   
           Dim item3 As New SyndicationItem( _
               "Item Three", _
               "This is the content for item three", _
               New Uri("http://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
   

3. Crie um objeto SyndicationFeed e adicione um autor, uma categoria e uma descrição.

   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");
   

   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")
   

4. Crie vários objetos SyndicationItem.

   SyndicationItem item1 = new SyndicationItem(
       "Item One",
       "This is the content for item one",
       new Uri("http://localhost/Content/One"),
       "ItemOneID",
       DateTime.Now);
   
   SyndicationItem item2 = new SyndicationItem(
       "Item Two",
       "This is the content for item two",
       new Uri("http://localhost/Content/Two"),
       "ItemTwoID",
       DateTime.Now);
   
   SyndicationItem item3 = new SyndicationItem(
       "Item Three",
       "This is the content for item three",
       new Uri("http://localhost/Content/three"),
       "ItemThreeID",
       DateTime.Now);
   

   Dim item1 As New SyndicationItem( _
       "Item One", _
       "This is the content for item one", _
       New Uri("http://localhost/Content/One"), _
       "ItemOneID", _
       DateTime.Now)
   
   Dim item2 As New SyndicationItem( _
       "Item Two", _
       "This is the content for item two", _
       New Uri("http://localhost/Content/Two"), _
       "ItemTwoID", _
       DateTime.Now)
   
   Dim item3 As New SyndicationItem( _
       "Item Three", _
       "This is the content for item three", _
       New Uri("http://localhost/Content/three"), _
       "ItemThreeID", _
       DateTime.Now)
   

5. Adicione os objetos SyndicationItem ao feed.

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

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

6. Use o parâmetro de formato para retornar o formato solicitado.

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

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

Para hospedar o serviço

1. Crie um objeto WebServiceHost. A classe WebServiceHost adiciona automaticamente um ponto de extremidade no endereço base do serviço, a menos que algum seja especificado em código ou configuração. Neste exemplo, nenhum ponto de extremidade é especificado para que o ponto de extremidade padrão seja exposto.

   Uri address = new Uri("http://localhost:8000/BlogService/");
   WebServiceHost svcHost = new WebServiceHost(typeof(BlogService), address);
   

   Dim address As New Uri("http://localhost:8000/BlogService/")
   Dim svcHost As New WebServiceHost(GetType(BlogService), address)
   

2. Abra o host de serviço, carregue o feed do serviço, exiba o feed e aguarde o usuário pressionar ENTER.

   svcHost.Open();
   Console.WriteLine("Service is running");
   
   Console.WriteLine("Loading feed in Atom 1.0 format.");
   XmlReader atomReader = XmlReader.Create("http://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("http://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();
   

   svcHost.Open()
   Console.WriteLine("Service is running")
   
   Console.WriteLine("Loading feed in Atom 1.0 format.")
   Dim atomReader As XmlReader = XmlReader.Create("http://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("http://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()
   

Para chamar GetBlog com um HTTP GET

1. Abra um navegador, insira a seguinte URL e pressione Enter: http://localhost:8000/BlogService/GetBlog.

   A URL contém o endereço base do serviço (http://localhost:8000/BlogService), o endereço relativo do ponto de extremidade e a operação de serviço a ser chamada.

Para chamar GetBlog() do código

1. Crie um XmlReader com o endereço básico e o método que você está chamando.

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

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

2. Chame o método estático Load(XmlReader), passando o XmlReader recém-criado.

   SyndicationFeed feed = SyndicationFeed.Load(reader);
   

   Dim feed As SyndicationFeed = SyndicationFeed.Load(atomReader)
   

   Isso invoca a operação de serviço e preenche um novo SyndicationFeed com o formatador retornado da operação de serviço.

3. Acesse o objeto de feed.

   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);
   }
   

   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
   

Exemplo

A seguir está a listagem completa de códigos deste exemplo.

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("http://localhost/Content/One"),
                "ItemOneID",
                DateTime.Now);

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

            SyndicationItem item3 = new SyndicationItem(
                "Item Three",
                "This is the content for item three",
                new Uri("http://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("http://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("http://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("http://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();
            }
        }
    }
}

Compilando o código

Ao compilar o código anterior, referencie a System.ServiceModel.dll e a System.ServiceModel.Web.dll.

Confira também

• WebHttpBinding
• WebGetAttribute