Developing Web Applications with Oracle ADF Essentials: Quickly build attractive, user-friendly web applications using Oracle's free ADF Essentials toolkit

The business service layer is doing most of the work that the application performs, such as delivering data, accepting instructions to create, change, or remove data, and performing more complicated calculations and operations. This layer interacts with the user interface part of the application through the use of ADF bindings.

There are several ways of building business services in an ADF application, but by far the easiest is to use ADF Business Components (ADF BC) based on database tables. This is the approach taken in this book and in many tutorials on ADF development. If you are just starting out with ADF, you should definitely master this way of building applications first.

Other alternatives are:

The ADF Business Components architecture has five types of components, listed as follows:

You can think of Entity Objects as representations of your database tables — there will be one entity object for every table your application uses.

Entity objects take care of the object-relational mapping and perform many optimizations for you; for example, entity objects cache data in the middle ties to save database round trips.

Similarly, you can think of Associations as representations of the relations between tables in your relational database –– there will normally be one association...

Through out this book, we will be building a small application based on the Sakila MySQL demo database, which contains data objects for a chain of DVD rental stores.

If you want to follow along in JDeveloper as you read, create a new application using the Fusion Web Application template. Navigate to File | New to bring up the New Gallery dialog box and in this dialog, navigate to Applications | Fusion Web Application (ADF).

In step 1 of the wizard, name your application something like RentalApp and provide an application package prefix that makes sense to you –– if you work for company.com, you could use com.company.adfdemo.

When you create an ADF business component (entity object, view object, and so on), JDeveloper initially creates only an XML file describing the object (which table, which attributes, and so on). Part of the XML file for an entity might look like as follows:

<?xml version="1.0" encoding="windows-1252" ?>
...
<Entity
  xmlns="http://xmlns.oracle.com/bc4j"
  Name="Film"
  Version="11.1.2.64.36"
  DBObjectType="table"
  DBObjectName="sakila.film"
...
  <Attribute
    Name="FilmId"
    IsNotNull="true"
    ColumnName="film_id"
    SQLType="SMALLINT"
    Type="java.lang.Integer"
    ColumnType="SMALLINT"
    TableName="sakila.film"
    PrimaryKey="true">
...
</Entity>

At runtime, the ADF framework automatically creates and runs the Java classes that read these XML files. For example, ADF creates an instance of the oracle.jbo.server.EntityImpl class whenever ADF needs to work with an entity object. The specific instance of the class reads the...

The ability to create your own Java implementation classes is a powerful feature, but it can be made even more powerful by inserting an extra layer in the object hierarchy.

If you generate Java as described previously, every one of your Java classes is wired directly to one of Oracle's classes. This is not a good idea –– in case you decide that you want some new feature built into every entity implementation class, you would have to change each of the individual classes (FilmImpl, RentalImpl, and so on).

Fortunately, there is a better way: you can create your own framework extension classes. These are sets of classes that extend the Oracle-supplied classes and sit between your specific implementation class and the Oracle-supplied class. For example, you can create your own com.company.adf.framework.EntityImpl class that extends the Oracle-supplied class (oracle.jbo.server.EntityImpl), and then let your specific implementation classes (for example, FilmImpl) extend...

In order to illustrate the process of building business components, we will build the necessary objects to show customers and their rentals. This will involve the following objects in the Sakila database:

Entity objects are created one-to-one, matching the database tables you will be using –– there are no design decisions to make when creating entity objects. View objects, on the other hand, represent the data you need for a specific use case or screen, so you need to have a good idea of the application you want to build before you can create useful view objects.

The storyboard

For the purpose of this book, we will be building a simple customer lookup screen, followed by a master-detail screen showing customers satisfying the search criteria; and for each customer, the films they have rented and not returned. It should look something like the following diagram:

Tip

Rough sketches of screens like these are called wireframes, and a collection of screens with navigation is called a storyboard. The preceding diagram was created with the specialized wireframing tool Balsamiq Mockups (http://www.balsamiq.com). It's a good idea for your organization to decide on a common tool to...

Now we have two view objects with all the data we need and we have defined the connection between them. The final business component we need to create is an Application Module. Navigate to File | New | Business Tier | ADF Business Components | Application Module to start the Create Application Module wizard:

This completes our business service layer. So far, we have created:

In many development teams, tasks are split between developers with some building business services and some building the user interface. Naturally, the developers building business services need a way to test their work without having to wait for the UI developers to finish their work. JDeveloper offers this in the form of the Business Components Tester.

To run this tester, simply right-click on the application module and select Run. This will start up the built-in tester application that will show the view object instances in your application module, as shown in the following screenshot:

You will be prompted for bind variable values when you activate a view object that needs them.

You can navigate through data, change data, and even create or delete records through the business component tester application.

We have built our own foundation classes for our business components and have created the business services we need for our simple example application. This includes entity objects and associations, view objects, view criteria, a view link, and an application module exposing our business service to the rest of the application. In the next chapter, we will be building the frontend of our application based on these business services.