Windows Azure: Service Bus Topics/Subscriptions入门

什么是Service Bus Topics/Subscriptions

Service Bus Topics/Subscriptions提供基于发布/订阅模式的消息通信模型，如图所示：

与Service Bus Queues不一样的是，Topics/Subscriptions使用发布/订阅模式实现了一对多的通信。就像我们订阅杂志，有若干个订阅方，同一本杂志可以根据订阅的数量发布给多个订阅者。我们可以理解成每一个Subscription就是一个Queue，发布者将消息发送给Topic，Topic再将消息复制多份，并发送到多个Queue中，且Queue之间不会互相影响，订阅者从对应的Queue中获取消息。在Topic将消息发送给Subscription的时候，可以设定过滤规则，假设发送的消息是订单信息，图中Subscription 1，我们可以设置成只接收来自北京的订单，则Topic只会将来自北京的订单消息发送给Subscription 1。

Service Bus Queues的优势所在同样适用于Service Bus Topics/Subscriptions，请参看Service Bus Queue入门。

如何使用Service Bus Topics/Subscriptions

使用Service Bus Topics/Subscriptions的方法与Service Bus Queues类似，同样需要引用相关程序集以及添加终结点配置，代码如下：

创建Topic

string topicName = "DataCollectionTopic";
NamespaceManager namespaceClient = NamespaceManager.Create();
TopicDescription topicDescription = null;
if (namespaceClient.TopicExists(topicName))
{
    topicDescription = namespaceClient.GetTopic(topicName);
}
else
{
    topicDescription = namespaceClient.CreateTopic(topicName);
}

创建Subscription

string subscription1 = "Subscription1";
string subscription2 = "Subscription2";

SubscriptionDescription subscriptionDescription1 = null;
SubscriptionDescription subscriptionDescription2 = null;

SqlFilter sqlFilter1 = new SqlFilter("IssueTitle = 'Package lost'");
SqlFilter sqlFilter2 = new SqlFilter("IssueTitle = 'Product damaged'");

subscriptionDescription1 = GetSubscription(topicName, namespaceClient, subscription1, sqlFilter1);
subscriptionDescription2 = GetSubscription(topicName, namespaceClient, subscription2, sqlFilter2);

private SubscriptionDescription GetSubscription(string topicName, NamespaceManager namespaceClient, string subscriptionName,Filter filter)
{
    SubscriptionDescription subscriptionDescription = null;
    if (namespaceClient.SubscriptionExists(topicName, subscriptionName))
    {
        subscriptionDescription = namespaceClient.GetSubscription(topicName, subscriptionName);
    }
    else
    {
        subscriptionDescription = namespaceClient.CreateSubscription(topicName, subscriptionName, filter);
    }
    return subscriptionDescription;
}

在创建Subscription时，我们使用了SqlFilter来做为Subscription的过滤器，SqlFilter对消息的Properties进行过滤。

发送消息

MessagingFactory factory = MessagingFactory.Create();
TopicClient topicClient = factory.CreateTopicClient(topicName);
BrokeredMessage message = new BrokeredMessage();
message.Properties.Add("IssueTitle", "Package lost");
topicClient.Send(message);

根据过滤规则，这条消息将被发送到subscriptionDescription1里面。

订阅方接收消息

string topicName = "DataCollectionTopic";
MessagingFactory factory = MessagingFactory.Create();
SubscriptionClient client = factory.CreateSubscriptionClient(topicName, subscriptionName, ReceiveMode.PeekLock);
BrokeredMessage message = client.Receive(TimeSpan.FromSeconds(1));
if (message != null)
{
    Console.WriteLine(string.Format("Message received: Id = {0}, Body = {1}", message.MessageId, message.GetBody<string>()));
    try
    {
        ProcessMessage();
        message.Complete();
    }
    catch
    {
        message.Abandon();
    }

}

 

具体例子采用用Winform客户端程序模拟发布方和订阅方，在订阅方，通过两个backGroundWorker组件来模拟分别从两个订阅中获取数据。

请点击 这里 下载源码。