As Published In
Oracle Magazine
May/June 2013

TECHNOLOGY: Oracle ADF

  

Calling Home

By Frank Nimphius

 

Here’s a bean reference technique to enable Oracle Application Development Framework regions to make callbacks to their parent pages.

One of the core architecture patterns in Oracle Application Development Framework (Oracle ADF) that promotes modular software design is the ability to expose bounded task flows in regions on a page. For a region to make callbacks to the owning page or view at runtime, developers typically use one of the following techniques: 

  • Contextual events, the messaging channel of the Oracle ADF binding layer, which enables Oracle ADF regions to establish bidirectional communication with other regions as well as the owning page or view.

  • The task flow parent action activity, which can be used to invoke a navigation case on a parent page or view. It’s a declarative option, however, that allows only navigation.

  • Bean reference, a technique in which a managed bean of the parent page task flow is passed as reference to a bounded task flow exposed in a region. The bounded task flow uses this reference to invoke a method on the managed bean, thus calling back into the parent task flow. 

Using contextual events, covered in two previous Oracle Magazine articles (see “Implement Contextual Events” and “Master and Commander”), is the most powerful technique for page-to-region and region-to-region interaction, and it also enables communication with nested regions. However, setting up contextual events is complex, and many developers balk at the unnecessary overhead for simple region communication use cases.

The bean reference technique explained in this article is easy to implement and well suited for many region communication use cases, making it an important part of the everyday toolbox of an Oracle ADF developer. This article explains how to configure and use a managed bean reference as a communication channel between a region and its parent page or view and includes a hands-on tutorial for you to walk through, using a provided sample application.

Note that for the rest of this article, the parent page task flow is referred to as the parent task flow. The page or page fragment (view) containing the region is referred to as the parent page.

Design-Time Architecture

As shown in Figure 1, the bean reference technique involves two managed beans. The first managed bean is defined in view scope of the parent task flow, and the other bean is defined in pageFlowScope of the bounded task flow that is exposed in the region.

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Figure 1: Bean reference technique design-time architecture

The managed bean of the parent task flow is passed as a reference to an input parameter that is defined on the bounded task flow exposed through the region. The bounded task flow saves the bean reference in a variable of its pageFlowScope bean. Using the reference to the managed bean in the parent task flow, the bounded task flow can then invoke methods on the bean or pass information to the parent task flow.

To understand why this technique works, it is important to review bean scopes and lifecycles. A managed bean configured in view scope lives as long as the page from which it is referenced remains active. The lifecycle of a task flow exposed in a region starts during the rendering of the parent page (unless the activation property is set to deferred). The task flow is dismissed when the application navigates away from the parent page, at which time the bounded task flow managed bean also becomes available for garbage collection.

As a result, both managed beans in our bean reference design—the managed bean in view scope of the parent task flow and the managed bean in page flow scope of the bounded task flow in the region—exist for as long as the parent view is shown. Because both beans live at the same time, it is safe to pass a bean reference from the parent task flow to the bounded task flow in the region without risking a null pointer exception or losing state.

Sample Application Overview

Figure 2 shows the runtime view of the application you will build by following the tutorial. The browser page contains two tables: one with department data and one with employee data. It also contains a read-only form showing data in the most recently selected table row.

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Figure 2: Updating the parent page form by selecting a row in a region

The page fragments that contain the departments table and the employees table are exposed by two separate regions. Whenever a user selects a new row in either the departments table or the employees table, the selected row data is sent from the bounded task flow in the region to the parent page for display.

Configuring the Sample Application

To follow the steps in this article, you need the studio edition of Oracle JDeveloper 11g Release 2 (11.1.2.3), available as a free download on Oracle Technology Network. You also need access to an Oracle Database instance with an unlocked HR schema. Get started by downloading the o33adf-1916752.zip sample application file and unzipping the file.

The first task is to change the database connection to point to your HR database schema:
  1. Launch Oracle JDeveloper 11g Release 2. From the Oracle JDeveloper menu bar, select File -> Open, and navigate to the directory containing the unpacked sample application.

  2. Open the OramagSample050613/Starter/RegionParentCommunication folder, and select the RegionParentCommunication.jws file. Click Open to load the workspace.

  3. From the View menu, select Database -> Database Navigator, and expand the RegionParentCommunication node to display the hrconn node.

  4. Right-click hrconn, and select Properties from the context menu. Edit the database connection information to work with your setup. Test the changes, and click OK

Next, start the Oracle WebLogic Server instance integrated with Oracle JDeveloper. To do so, select Start Server Instance from the Run menu. 

If this is the first time you’ve run the integrated Oracle WebLogic Server, a Create Default Domain dialog box will open. Create a password for the default Oracle WebLogic Server domain, and select an address from those listed for Listen Address. For example, choose localhost rather than leaving the address empty.

Click OK to save the changes and to create and configure the Oracle ADF default domain.

Hands-on Overview

The RegionParentCommunication.jws workspace you opened in Oracle JDeveloper 11g Release 2 is the starting point for the following hands-on instructions. All the task flows, page fragments, and implementation code have already been prepared, so you can focus on configuration of the region-to-parent-page communication.

You will perform the following tasks in this tutorial:

  • Set up the departments task flow to accept a managed bean reference as an input parameter, and store the bean reference in a managed bean you create in the departments task flow pageFlow scope. Note that this step has already been done for the employees task flow to save you from unnecessary repetition.

  • Override the SelectionListener property of the Oracle ADF Faces table within the DepartmentsView.jsff fragment to post selection change notification to the task flow of the parent page.

  • Create a managed bean in view scope of the parent task flow to be passed as an argument to both the employees task flow and the departments task flow.

  • Add the two regions to the parent page, and reference the viewScope managed bean as an input parameter.

Because parts of the sample application have already been created, it is important that you follow the hands-on instructions closely. A completed sample, for which you need only to configure database access, is provided in the download. 

Setting Up the Department Task Flow

For the departments task flow to hold a reference to a managed bean defined in the parent task flow, you need to create a managed bean in the bounded task flow to store the bean reference. You also need an input parameter that receives the reference at runtime. Follow the steps below to complete those tasks:
  1. In the Oracle JDeveloper Application Navigator, expand the ViewController project in the RegionParentCommunication workspace.

  2. Expand the Application Sources folder, and navigate to the btf package node within the oramag.mayjun.thirteen.view.beans package.

  3. Right-click the btf node, and choose New from the context menu.

  4. In the New Gallery dialog box, select General -> Java and then Class.

  5. Click OK.

  6. In the Create Java Class dialog box, set the value of Name to DepartmentsPageFlowBean.

  7. Click the magnifier icon next to the Extends field to open the class browser.

  8. In the class browser, select the Hierarchy tab and scroll to the oramag package node.

  9. Expand the oramag -> mayjun -> thirteen -> view -> beans -> shared package nodes.

  10. Select the TaskFlowPageFlowBean class, and click OK twice.

  11. In the Java editor that appears, add the following line above the class constructor:  

    private ParentHandle parentHandle = null; 


    When you type the line above, the Importing pop-up dialog box will appear to import the class. Type Alt + Enter to confirm the import.

  12. Select the parentHandle variable with the right mouse button, and choose Generate Accessors from the context menu to create a pair of setter and getter methods.

  13. Select OK in the Generate Accessors dialog box, after ensuring that the setParentHandle and getParentHandle methods are selected.

  14. Save your work.

    At this point, you have successfully created the Java class you will configure in the next step as a managed bean in the departments task flow. The ParentHandle class variable will later store the reference to the parent task flow managed bean.

    Note that ParentHandle is a Java interface class that defines the contract between the parent flow bean and the managed bean in the bounded task flow that stores the reference. The TaskFlowPageFlowBean class, one of the precreated helper classes in this sample, contains the implementation details for the bounded task flow for passing row data to the parent page. By extending this class, you have fully implemented the functionality required by the sample.

    The next step is to configure the DepartmentsPageFlowBean class as a managed bean in pageFlow scope in the departments task flow. 

  15. In the ViewController project, expand the Web Content -> WEB-INF and btf folders.

  16. Double-click the departments-task-flow.xml file to open the task flow in the diagram editor.

  17. In the departments-task-flow.xml diagram, click the Overview tab at the bottom.

  18. Select the Managed Beans menu entry, and click the green plus (+) icon to the right of the Managed Beans label.

  19. Set the Name field value to departmentsFlowBean, and click in the Class field.

  20. Click the down-arrow icon on the right and then the Edit menu entry to open the class browser.

  21. Select the Hierarchy tab (if it’s not already selected), and scroll to the oramag package node. Expand the oramag -> mayjun -> thirteen -> view -> beans -> btf node, and select DepartmentsPageFlowBean. Click OK.

  22. Set the Scope field to pageFlow so the managed bean is accessible as long as the departments task flow instance is active.

  23. Save your work.

    Next create a new input parameter for the departments task flow that expects an input value of type ParentHandle to save in the departmentsFlowBean you just configured.

  24. Go back to the opened departments-task-flow.xml window, and make sure the Overview tab is selected at the bottom.

  25. Select the Parameters menu entry, and click the green plus (+) icon to the right of Input Parameter Definitions to create a new input parameter.

  26. Set the Name field value to parentHandle, and click in the Class field.

  27. Click the down-arrow icon on the right and then the Edit menu entry to open the class browser.

  28. Select the Hierarchy tab (if it’s not already selected), and scroll to the oramag package node. Expand the oramag -> mayjun -> thirteen -> view -> beans -> interfaces package nodes, and select the ParentHandle interface class.

  29. Click OK.

  30. Click in the Value field. Click the down-arrow icon on the right, and choose Expression Builder from the context menu.

  31. In the Expression Builder dialog box, expand the ADF Managed Beans and pageFlowScope folders.

  32. Expand the departmentsFlowBean node, select parentHandle, and click OK.

  33. Check the Required checkbox, and save your work.

In this section, you created a managed bean you will reference as the value target of a new bounded task flow input parameter. 

Overriding the Departments Table Selection Listener

Now that the departments task flow is configured, the next step is to wire up the table with the managed bean in pageFlow scope. This step will enable selected row data to pass to the parent page whenever a user selects a table row in the user interface. To perform this task, you need to override the SelectionListener of the table, as shown below.
  1. In the task flow diagram that shows the contents of the departments-task-flow.xml file, double-click the DepartmentsView activity to open the page.

  2. In the page editor, click the af:table#t1 bread crumb at the bottom of the visual editor window to select the table.

  3. In the Property Inspector, navigate to the SelectionListener property within the Behavior category. If the Behavior category is not yet expanded, expand it by clicking the + icon.

  4. Click the down-arrow icon on the right-hand side of the SelectionListener property field, and choose Edit from the context menu to bring up the Edit Property: Selection Listener dialog box.

  5. Select departmentsFlowBean from the Managed Bean list.

  6. Click the New button next to the Method field to create a new managed bean method to handle the selection event.

  7. In the Create Method dialog box, define the MethodName as onRowSelect and click OK twice.

  8. Select the DepartmentsPageFlowBean .java tab, the first tab in the Oracle JDeveloper code editor area. (This is the first file you opened in this tutorial.)

  9. Navigate to the onRowSelect( SelectionEvent selectionEvent) method, and place the cursor within the code braces.

  10. Add the following code to invoke a precreated method on the bean’s superclass:  

    super.onRowSelect(selectionEvent, parentHandle);
    
  11. Save your work, and close all opened tabs by clicking the x at the right side of each.

In this section, you changed the default row selection behavior, and by doing so, you synchronized the table selection with the Oracle ADF binding layer to invoke a method on the managed bean superclass. The onRowSelect method of the superclass does two things: it synchronizes the user row selection with the binding layer, and it notifies the parent task flow bean about the selection change. To handle these tasks, it uses the parentHandle variable you passed in as an argument. 

Configuring the Parent Task Flow Bean

In this sample application, the managed bean that dispatches the messages sent from the regions to the parent page is configured in the unbounded task flow definition (adfc-config.xml). To build and configure the managed bean, follow these steps:
  1. In the ViewController project, expand the Application Sources folder and navigate to the beans package node within the oramag.mayjun.thirteen.view node.

  2. Right-click the beans node, and choose New from the menu that appears.

  3. In the New Gallery dialog box, select the General -> Java node.

  4. From the right-hand list, select Class, and click OK.

  5. In the Create Java Class dialog box, add the Name field value ParentPageBean.

  6. In the Package field, append .parent to the current package name so it reads oramag.mayjun.thirteen.view .beans.parent.

  7. In the Optional Attributes section, click the green plus (+) icon next to the Implements label to implement an interface class.

  8. In the class and package browser, switch to the Hierarchy tab (if it’s not already selected) and navigate to the oramag -> mayjun -> thirteen -> view -> beans -> interfaces package node.

  9. Expand the interfaces package node, and select ParentHandle. Click OK twice.

  10. Save your work.

    In this section, you created the managed bean for the parent task flow and implemented the ParentHandle interface, which defines the communication contract between the region and the parent bean through the notifyParent method. If you use this technique in your custom Oracle ADF application projects, you can define additional methods. 

    Next, add the implementation code to the managed bean so that the parent page updates whenever the regions pass data. 

  11. Expand the ViewController -> Resources node in the Application Navigator, and double-click ParentPageBean.txt.

  12. Copy the contents of the ParentPageBean.txt file to the clipboard by pressing Ctrl + A followed by Ctrl + C.

  13. Copy the contents of the clipboard to the ParentPageBean.java class by selecting the ParentPageBean.java tab, clicking in the class, and pressing Ctrl + A followed by Ctrl + V.

  14. Save your work, and close all tabs.

    Next, configure ParentPageBean.java as a managed bean in the parent task flow (adfc-config.xml).

  15. In the Oracle JDeveloper Application Navigator, expand the ViewController -> Web Content -> WEB-INF folder and double-click the adfc-config.xml file.
  16. In the opened adfc-config.xml diagram, click the Overview tab at the bottom.
  17. Select the Managed Beans menu entry, and click the green plus (+) icon next to the Managed Beans label.
  18. Click in the Name field, and change the default name to ParentPageBean.
  19. Click in the Class field. Click the down-arrow icon on the right, and select the Edit menu entry to open the class browser.

  20. In the Edit Property dialog box, switch to the Hierarchy tab (if it’s not already selected).
  21. Navigate to and expand the oramag -> mayjun -> thirteen -> view -> beans -> parent package node.
  22. Select the ParentPageBean class, and click OK.
  23. Finally, for the Scope field value, select view from the list.
  24. Save your work.

Adding the Regions to the Parent Page

Next Steps

  

DOWNLOAD
 Oracle JDeveloper 11g
 the sample application for this article

LEARN more about contextual events
 Implement Contextual Events
 Master and Commander

Almost there! The next step is to add the departments task flow (departments-task-flow.xml) and the employees task flow (employees-task-flow.xml) to the ParentPage.jsf file as a region. Note that the employees task flow has been fully precreated for this tutorial, so there is no need for you to build it first. 

To perform this task, you need to pass the ParentPageBean managed bean reference as an input argument to the region to set up the communication link.
  1. In the Application Navigator, expand the ViewController -> Web Content -> pages double-click ParentPage.jsf. The file will open in the visual editor.

  2. Expand the ViewController -> Web Content -> WEB-INF -> btf folder.

  3. Drag and drop the departments-task-flow.xml file into the Departments Region area in the visual editor, as shown in Figure 3.

     

    o33adf-f3

    Figure 3: Creating the departments region

  4. In the opened Create dialog box, select the Region menu entry.

  5. In the opened Edit Task Flow Binding dialog box, click in the Value field with the red border around it. (If you don’t see this dialog box, you most likely forgot to check the required checkbox for the task flow input parameter as explained in step 33.)
  6. Click the down-arrow icon, and choose Expression Builder from the menu.
  7. In the Expression Builder dialog box, expand the ADF Managed Beans -> viewScope node and select ParentPageBean.
  8. Click OK twice to create the region.
  9. Repeat steps 71 through 76 for the employees-task-flow.xml task flow definition, but drop it in the Employees Region page area. Save your work. 

Running the Sample 

The ParentPage.jsf page contains an output text box for displaying the region ID of an incoming message as well as an af:forEach Oracle ADF Faces tag to print the message sent from the bounded task flow. Both UI components of the Oracle ADF Faces feature of Oracle ADF reference the ParentPageBean managed bean, which is why it was important that you used the names suggested in this tutorial. 

Run the page by following the steps below:
  1. In the Application Navigator, expand the ViewController -> Web Content -> pages node and right-click the ParentPage.jsf page.

  2. Choose Run from the menu that appears.

  3. Once the page is displayed in the browser, select a row in the departments table or the employees table that is not currently selected to see the region-to-parent-page communication shown in Figure 2. 

Conclusion

This article explained a technique for establishing region-to-parent-page communication by using a managed bean reference. Although the article doesn’t cover it, you can also extend this technique by using the parent task flow as a dispatcher to implement bidirectional region-to-region interaction—a testament to the power of this approach. By using bounded task flow templates to define the bounded task flow input parameter and managed bean, you can make the bean reference technique a part of your overall task flow design strategy. This approach adds a powerful new tool to your Oracle ADF toolbox.


 Frank Nimphius is a senior principal product manager for Oracle JDeveloper and Oracle ADF. He is a coauthor of Oracle Fusion Developer Guide: Building Rich Internet Applications with Oracle ADF Business Components and Oracle ADF Faces (McGraw-Hill, 2010).


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