XML Event Builder

XML Event Builder converts the events/streams from an input adaptor that supports XML input streams into an event stream that is compatible with the event processor. The event attributes are extracted using XPath expressions and converted to the type specified in the mapping before sent to the event processor.

You can configure through the management console as explained below or by manually adding an XML file as explained in step 5.

Start the CEP, log in to its management console, select Event Builders and click Add Event Builder.
Enter details in the form that appears and click the Add Event Builder button at the end of the form. For example,

The fields in the above configuration are as follows:
- Event Builder Name : Property to uniquely identify an event formatter configuration
- Input Event Adaptor (marked as 1 in the screenshot) : The input event adaptor used to publish events to the CEP. This drop-down list only displays the adaptors that are already created. In this example, we select an Input WS-Event Local Event Adaptor already created.
- Input Event Adaptor properties (marked as 2 in the screenshot) : Properties required by the input event adaptor depending on the input event adaptor type selected before. For example, if you select an event adaptor that supports XML, then the required properties are:
  - Topic - The topic to which event publishers publish events to
- Input Mapping Type (marked as 3 in the screenshot): Select xml as the mapping type. This property changes based on the event adaptor selected. It lists only the mapping types supported by a particular event adaptor.
- Mapping properties (marked as 4 in the screenshot) : Map the incoming stream to the outgoing stream received by the event processor. Provide the necessary details in the input fields:
  - Enter the xpath prefix and namespace in Prefix and Namespace under XPath prefixes
  - Click Add under XPath prefixes to add the namespace and prefix.
  - Enter the Input Attribute Name , XPath and To Stream Data Type under 'Properties'
  - Click Add to add the individual attribute mapping to the event builder
    
    For the correct properties to show, you must selected an event adaptor that supports XML mapping type.
- To Stream Name/Version : Stream name/version of the outgoing stream
After a builder is successfully created, you can change its configuration and redeploy it. To do this, click the Edit link associated with it. You can also click the other links associated with it to delete or enable statistics and tracing.
An XML based editor opens allowing you to edit the event builder configuration from the UI itself, without having to edit the file in the file system. Do your modifications and click Update.

Alternatively, you can specify an event builder configuration using an XML file and save it in <PRODUCT_HOME>/repository/deployment/server/eventbuilders directory, which is the event builder deployment directory. Since hot deployment is enabled, you can simply add/remove files to deploy/undeploy from the server.

Create the XML file with the following XML based event builder configurations. Event builder implementation must start with <eventbuilder> root element and the namespace set to http://wso2.org/carbon/eventbuilder as in the example below:

<?xml version="1.0" encoding="UTF-8"?>
<eventBuilder name="xmlbuilder" xmlns="http://wso2.org/carbon/eventbuilder">
  <from eventAdaptorName="localWsEventReceiver" eventAdaptorType="ws-event-local">
    <property name="topic">AllStockQuotes</property>
  </from>
  <mapping type="xml" batchProcessingEnabled="true" >
    <xpathDefinition namespace="http://ws.cdyne.com/" prefix="quotedata"/>
    <property>
      <from xpath="//quotedata:StockQuoteEvent/quotedata:LastTradeAmount"/>
      <to name="price" type="double"/>
    </property>
    <property>
      <from xpath="//quotedata:StockQuoteEvent/quotedata:StockSymbol"/>
      <to name="symbol" type="string"/>
    </property>
  </mapping>
  <to streamName="stockQuotes" version="1.0.0"/>
</eventBuilder>