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WebObjects Viewed Through Its Classes

As you learned at the end of the first chapter, WebObjects applications respond to HTTP requests and return responses in the form of dynamically generated HTML pages. The main loop of a WebObjects application, in which the application performs this work, is called the request-response loop. You have a very broad understanding of how this works: the web browser sends a request to the HTTP server, which forwards it to the WebObjects adaptor, which translates it into a form that a WebObjects application can understand. For the response, the process is reversed.

This chapter describes in much greater detail what happens during the request-response loop. It does so by describing the request-response loop as WebObjects views it: as a communication between objects. In this chapter, you learn about the objects that are involved at each level of the loop, each object's duty during each part of the request-response loop, and the way these objects generate an appropriate HTML page in response to the user request. You also learn about the two varieties of request handling (component action and direct action) and exactly how these two differ.

In the chapter "Common Methods", you learned some of the methods that are invoked during the request-response loop, and you learned about cases where you might want to override these methods. As you write more complex WebObjects applications, it becomes necessary to know exactly what happens at each point in the processing of an HTTP request and the generation of an HTTP response. You should read this chapter to learn that level of detail. You can also refer to the class specifications in the online book WebObjects Class Reference.

The Classes in the Request-Response Loop

Server and Application Level

Session Level

Request Level

Page Level

Database Integration Level

How WebObjects Works-A Class Perspective

Starting the Request-Response Loop

Determining the Request Type

Handling Component Action Requests

Accessing the Session

Creating or Restoring the Request Page

Taking Input Values From a Request

Invoking an Action

Generating the Response

Request Post-Processing

Handling Direct Action Requests

Invoking the Action

Generating the Response

Request Post-Processing

Component Actions vs. Direct Actions

How HTML Pages Are Generated

Component Templates

Associations and the Current Component

Subcomponents and Component References

First Section