Apple WebObjects 3.5 Instrukcja Użytkownika Pobierz pdf (Strona 72)

Chapter 5 WebObjects Viewed Through Its Classes

dynamic elements on your page and the objects in the Enterprise Objects

Framework.

• EOEditingContext (in Java, next.eo.EditingContext)

Manages a graph of objects fetched from a database. The objects represent

tables, rows, and columns in the database.

When a WebObjects application accesses a database, one or more of the

components in the application contain one or more WODisplayGroup objects.

The session object provides access to an EOEditingContext object that is used,

for example, when changed data is saved to the database. Each session uses an

EOEditingContext to manage graphs of objects fetched from a database and to

ensure that all parts of an application remain synchronized. For read-only

applications, you can customize WOSession to return a per-application

EOEditingContext.

For more information on how the WebObjects and Enterprise Objects classes

interact, see the Enterprise Objects Developer’s Guide.

How WebObjects Works—A Class Perspective

You’ve now had a brief introduction to the classes used in WebObjects. This

section describes the sequence of events that happen during a cycle of the

request-response loop—how the application starts up, what happens when it

receives an HTTP request, and how it processes that request.

Starting the Request-Response Loop

A WebObjects application can start up in one of two ways: automatically, when

it receives a request (autostarting), or manually, when it’s run from the command

line. Either way, its entry point is the same as that of any C program: the

main

function. In a WebObjects application,

main is usually very short. Its job is to

create and run the application.

The

main function begins by creating an autorelease pool that’s used for the

automatic deallocation of objects that receive an

autorelease message. It then calls

a function that loads the Java Virtual Machine (VM) if necessary.

The next step is to create a WOApplication (or WebApplication) object. This

seems fairly straightforward, but in the

init method or constructor the application

creates and stores, in an instance variable, one or more adaptors. These adaptors,

all instances of a WOAdaptor subclass, handle communication between an

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Apple WebObjects 3.5 Instrukcja Użytkownika Strona 72