About Event Handlers

Event handling is a feature in Verastream Host Integrator that extends the capabilities of Host Integrator models by allowing you to define specific events that suspend the interpretation of a model and turn control over to user-supplied procedural code.

One use of event handlers is to improve the presentation of host data in new client applications. For example, you can use event handlers to:

• Convert cryptic host application codes to user-friendly descriptions
• Convert formats for currencies or dates
• Secure access to sensitive data
• Create other functions that might otherwise require custom client-side programming

You can also use event handlers to extend the Host Integrator error-handling capabilities. For example, you can add an event handler at the point the error occurs and then implement event-handler code that intercepts the error, takes control, and corrects the error.

Implementing Event Handlers

You can attach an event handler to any of the following model objects. For each of these eight varieties of event handler, there are one or more defined events. Click each model object type to see details on the events and possible uses for event handlers associated with each.

• The model
• The "life cycle" (events such as Model Load, Model Unload, Authenticate User) that occur as the server manages sessions with the model.
• An entity
• An attribute
• An operation
• A recordset
• A recordset field
• A procedure

Use the event handler guidelines as a starting point for implementing event handlers. A set of event handler examples are available as part of the Host Integrator Development Kit.

Creating, Building, and Deploying Event Handlers

Use the Design Tool to review and select event handler attachment points, configure your event handler development options, and build event handler templates. (The templates are code stubs that provide a starting point for your own event handler.) You can build, load, attach, and test event handlers within the Design Tool.

The current version of Host Integrator supports development of event handlers in Java. After you create an event handler template in the Design Tool, you can implement the handler with any appropriate third-party editor. Event handlers are packaged and deployed with a Host Integrator model.

Once event handlers are deployed, they are managed by the script manager, which runs with both the Design Tool and the Session Server. An event source is a specified point in the execution of a model, such as the reading of an attribute, the authentication of a user, or the writing of a recordset field. An event source generates an event only if the corresponding event method is implemented in the attached event handler. The event delivered to the event handler describes the environment in which the event occurred. The event handler code uses this description to accomplish its task.