Application Service Listener Background

Introduction    Implementing    Background

• Request Flow from HTML Page to Websydian Application
• Data from Application to Websydian Server

Request Flow from HTML Page to Websydian Application

For details on how parameters are passed from the HTML page to the Websydian application please refer to Dispatcher Background. These steps also applies to a Websydian application implemented in one of the DWA variants.

Because of the introduction of a Relay Service component on the web server and an Application Service Listener function some extra steps are needed in order to describe the flow of a request from a browser to the web server.

The flow of a request is illustrated in the figure below.

Each step is described in detail below:

1. The end user activates an event in the browser by pressing a button or clicking on a link.
2. Based on the information in the HTML page the browser will generate a request and send it to the web server. The request contains parameters entered by the user or parameters stored in the HTML page as hidden fields.
3. Based on the information in the request the web server can identify the Relay Service that should handle the request. The Relay Service is called and all information about the request is made available for the Relay Service.
4. The Relay Service will retrieve all parameters from the request and send them to the Application Service Listener function using a TCP/IP connection.
5. The Application Service Listener function receives the parameters from the Relay Service and transfers them to the Dispatcher function.
6. When the Dispatcher function is called the Websydian application flow continues by calling the appropriate Event Handler and Page Generator functions. Please refer to The Websydian Circle for more details on the relationship between the Event Dispatcher, Event Handler and Page Generator functions.
7. The Page Generator function sends the generated HTML page to the Relay Service over the same TCP/IP connection used by the Application Service Listener function.

8. Once control is returned to the Application Service Listener function, it will inform the Relay Service that the processing of the request has completed and the HTML page safely can be returned to the browser.

9. The Relay Service returns the HTML page to the browser.

Please refer to DWA Background for details on how the Relay Service communicates with the Application Service Listener function and how information is exchanged between the two parties.

Data from Application to Websydian Server

The Websydian Server is already becoming a central repository for application information, and in future versions of Websydian this development continues, as the Websydian Server gets even more powerful.

Several approaches are used to pass information to the Websydian Server about the application. When starting the Application Service Listener, it is possible to set a number of options, and this information is passed on to the Websydian Server. Also, the Application Service Listener extracts information from the model and passes that information to the Websydian Server.

In order for the Application Service Listener to extract information from the model it is necessary to specify the correct inheritance. How to do that is described in the Implementing section.