Working with Topics and Events

Events are notification messages published to a specific topic. Web services can subscribe to a topic in order to receive events that are published to it, allowing web services to publish and subscribe to each others' notifications.

The Topic Browser in the Management Console allows you to create, manage, and subscribe to topics, and the Event Mediator makes it easy for your proxy service or sequence to publish a received request or response to a topic as an event. Eventing in the ESB of WSO2 Enterprise Integrator (WSO2 EI) is based on the WS-Eventing Specification. The following pages describe how to work with topics in detail:

Adding a new topic

Follow the instructions below to add a new topic directly to the root.

1. Sign In. Enter your user name and password to log on to the ESB profile's management console.
2. Click the "Main" button to access the "Manage" menu.
   
3. Click on "Add," under "Topics", to access the "Add Topic" page.
   
4. On the "Add Sub Topic" page, enter a name of the new topic in the "Topic" field.
   
   You can also choose whether to subscribe and publish the topic or not in the corresponding check boxes.
   
5. Click the "Add Topic" button.
   
6. The "WSO2 Carbon" window appears. Click "OK."
   
7. The new topic is shown in the topics tree.
   

Adding a new sub topic

The "Add Subtopic" feature provides user the ability to add a topic under the existing topic. When adding a new topic under an existing topic, user can provide the name of the new topic and set the permissions for publishing and subscribing for that topic.

Follow the instructions below to add a subtopic.

1. Sign In. Enter your username and password to log on to the ESB profile's management console.
2. Click the "Main" button to access the "Manage" menu.
   
3. Click on "Browse," under "Topics", to access the "Topic Browser" page.
   
4. The "Topic Browser" page appears. Click on the topic you want to add a subtopic to.
   
5. Click on the "Add Subtopic" link.
   
6. On the "Add Sub Topic" page, enter a name of the new subtopic into the "Topic Name" field.
   
   You can also chose whether to subscribe and publish the subtopic or not in the corresponding check-boxes.
   
7. Click the "Add Topic" button.
   
8. The "WSO2 Carbon" window appears. Click "OK."
   
9. The new subtopic is shown in the topics tree of the Topic Browser screen.
   

Viewing details of a topic/subtopic

Each topic has specific details such as permissions, WS subscription details, and JMS subscription details. In the Topic Browser screen appears. Click the Details link of the topic you want to see the details of.

The "Topic Details" page appears.

All the details related with a topic can be viewed on this page. The following details are available:

• • Permission Details - Allows to view the permissions related with the topic.
  • WS Subscription Details - Shows all the WS subscriptions for the topic and all its children.
  • JMS Subscription Details - All the durable and non durable JMS subscriptions are listed here.
  • Publish - Allows the user to publish a sample XML message to a topic.

Permission Details 

If you want to change the permission details, proceed to the following steps:

1. 1. Chose the role of the topic and change the ticks on the provided check boxes.
      
   2. Click on the "Update Permissions" button.
      
   3. The "WSO2 Carbon" window appears. Click "OK."

WS Subscription Details 

Using "Ws Subscription Details" the user can unsubscribe or renew the subscription.

Unsubscribing

Use the following instructions to unsubscribe.

1. Choose the necessary subscription and click on the "Unsubscribe" link.
   
2. In the "WSO2 Carbon" window, click "OK" to confirm your request.
   

Renewing the Subscription

Follow the instructions below to unsubscribe.

1. Choose the necessary subscription and click on the "Renew" link.
   
2. The "Renew Subscription page appears," fill in the required fields.
   

   

   Tip

   See the detailed description of the fields in Subscribing to a Topic.

3. Click the "Renew" button.
   
4. In the "WSO2 Carbon" window, click "OK" to confirm your request.
   

Publish 

Follow the instruction below to publish XML message.

1. Place a XML message in the provided space.
   
2. Click "Publish."
   
3. In the "WSO2 Carbon" window, click "OK" to confirm your request.
   

Subscribing to a topic/sub topic

The subscription allows to receive events published to the specified topic and all its children. In the Topic Browser page, click Subscribe on the topic you want to add a subscription to.

The following options are available:

• • Topic - User does not need to specify the topic here, since its automatically sets up.
  • Subscription Mode- This is the mode of the subscription and there are tree modes:
    • "Topic Only" - The default mode for the subscription. With this mode, user creates the subscription only to the topic. In that mode subscribers only receive events, which are published only to the that topic.
    • "Topic and Immediate child" - Allows to receive events published not only the specified topic, but also to the immediate child of that topic.
    • "Topic and Children" - Allows to receive events published to the specified topic and all its children
  • Event Sink URL - This is the URL which the subscriber should provide to receive events published. When events are published to the topic, they are sent to the specified URL here.
  • Expiration Time - Here user can specify the expiration time of the subscription. This is not a required parameter and if user leave it alone, subscription will never be expired.