ADF Interview Questions - Set 8

Question: What is Query Collection in VO?

Answer: Query Collection is mainly used for caching the result of the executed query VO. A VO can have multiple query collections depending on the rowsets.

Example: If we have 2 rowsets where DEPTID =10 and DEPTID=20. So the results of the executed VO with these bind variables are stored in Query Collection.

Now we understood what are the other layers that are to be used before hitting the data source? Now let us see how it will be executed with an example: 

Example:  Let’s consider a java code snippet where we execute a VO and retrieve the values 

          ViewObject vo = ApplicationModule.findViewObject(“EmployeesVO”);

           vo.executeQuery(); 

           Row row = vo.first();                                          // gets the first row

     Steps involved in executing this VO are as follows: 

1.     ADF client starts interaction with the Application Module. 

2.     ADF Client looks for the requested View Object (EmployeesVO) instance in AM.

3.     Now before executing the VO, it does as below: 

a.     Checks for relevant Query Collection for Search Parameters (Bind Variables), if available uses the existing query collection.

b.    If not present created a new Query Collection based on the Search Parameters.

4.     Once the QC is initialized, the new Rowset instance calls the prepareRowSetQuery() on VO. This is used for placing your customcode before Querycollection. (Eg: the Query for the rowset with the bind variable).

5.     This is followed by executeQueryForCollection(), which delegates the call for query collection instance and JDBC call for particular Database. 

6.     Now when a client tries to get the first row in result set by calling first() , as the result set retrieves the first row it displays the first row.

Question: How and When Groovy Expression is used?

Answer: Groovy is interpreted at runtime; it can be treated as metadata and customized. So, you could have an application that has customized business rules in Groovy and those customizations stored in Oracle ADF’s Metadata Services (MDS).

Oracle ADF provides a number of different declarative points into which you can drop Groovy code:

1.     Values for view and entity objects attributes

2.     Validation rules on entity object attributes

3.     Expressions for error messages

4.     Values for view object bind variables

5.     View object transient attribute validation.

Examples:

1: For the transient attribute AnnualSalary you could define a Groovy expression for the default to be: Sal * 12

2: On the Sal attribute you might want to define that a salesman must have a salary of less than 1000: if (Job == "SALESMAN") {return newValue < 1000} else return true.

ADF Business Components view objects also provide the ability to use Groovy expressions. As with entity objects, view objects can support:

1.     Referencing attributes in the same view object

2.     Referencing attributes in other view objects

3.     Transient attribute validation

4.     Referencing methods in the Java class that backs the view object

5.     Referencing built in calls such as sum and min.

Question: What are the steps to configure MDS? What are different kinds of MDS you configured? Which file hold details of configured MDS?

Answer: To apply MDS to your application follow this:

1. Pages should be (.jspx) not (.jsp).

2. In your project properties --> ADF View check on "Enable User Customizations" then select "Across Sessions Using MDS".

3.Create a new class as below. This class has two main functions:

- getName() which return the folder name that hold all users changes.

- getValue() which return the folder name for the login user. This folder should be unique for every login user and will saved inside the getName() folder.

4. In Application Resources --> Descriptors --> ADF META-INF open adf-config.xml.

5. In adf-config file go to MDS Configurations and add your class

6. In adf-config file go to View tab and add all Tags.

7. Now you apply MDS to your application.

8. If you run your application in Integrated Weblogic there will be no problem, you should only specify the path to store the user changes (changes will stored in file system). You will find this path in your Application properties --> Run --> MDS.

ADF Interview Questions - Set 7

Question: Explain briefly the life-cycle phases of JSF?

Answer: The six phases of the JSF application lifecycle are as follows:

1. Restore View: A request comes through the FacesServlet controller. The controller examines the request and extracts the view ID, which is determined by the name of the JSP page.
2. Apply request values - process events: The purpose of the apply request values phase is for each component to retrieve its current state. The components must first be retrieved or created from the FacesContext object, followed by their values.
3. Process validations - process events: In this phase, each component will have its values validated against the application’s validation rules.
4. Update model values - process events: In this phase JSF updates the actual values of the server-side model ,by updating the properties of your backing beans.
5. Invoke application - process events: In this phase the JSF controller invokes the application to handle Form submissions.
6. Render response: In this phase JSF displays the view with all of its components in their current state.

Question: Write code to access the current row and or the view object inside your bean?

Answer: Code to access the current row and or the view object inside your bean:

BindingContainer bc = BindingContext.getCurrent().getCurrentBindingsEntry();

DCBindingContainer dcbc = (DCBindingContainer) bc;

DCIteratorBinding lBinding = dcbc.findIteratorBinding("EmployeesViewIterator");

EmployeesViewRow row = (EmployeesViewRow) lBinding.getCurrentRow();

EmployeesView view = (EmployeesView) lBinding.getViewObject();

Question: What is Action Listener?

Answer: An action listener is a class that wants to be notified when a command component fires an action event. An action listener contains an action listener method that processes the action event object passed to it by the command component.

Question: What are mutable and immutable objects?

Answer: An immutable class is immutable, as in, it is not mutable. You cannot change it. If you have x::String, you can be absolutely 100% certain that x will never ever change ever (or at least, if it does, people are abusing the flexibility of your language and you have every right to tell them where to go).

A mutable class is not immutable. You can change it, other people can change it, and you can't rely on it being the same. It could be changed in another thread; you can't even be sure of it being in the same state from line to line unless you have good locking.

Question: What is Application module pooling and how can we handle it?

Answer: An application module pool is a collection of application module instances of the same type, such as an Orders application module or a Human Resources application module. This pool of application module instances is shared by multiple browser clients. The amount of time between submitting Web pages enables a smaller number of application module components to serve a larger number of active users. This reduces memory usage and improves performance.
This facility manages a configurable set of application module instances that grows and shrinks as the end-user load on your application changes during the day.

At any one time, the pool may contain application module instances that are partitioned into
three groups, based on their state. When the processing of a current HTTP request completes, the application module instance is checked back into the pool. If the AM instance has managed state, the pool keeps track that the AM is referenced by that particular session.
For example – We have pool of 5 Application module instances. After having request from multiple browsers, request will go to instance, which is available for time being. We have 3 state defined for appModule instances –
1- Available
2- Partially available- but referenced for preferred reuses by another active session that would be more efficient due to the managed state of the application module.
3- Unavailable- because it is being used at that very moment by a Web container thread

Note: Pools are created only for root application modules, not for nested ones that users access indirectly through a root application module.

In short –

Application module pooling:

• Enables users to share application modules
• Manages application state
• Provides the same instance or one with an identical state
when requested by an application with managed state

Question: How can we prevent unauthorised access to the ADF DC Model?

Answer: By using Bounded Task Flow

Question: How can we share AM for using same transaction?

Answer: By using AM Module Pooling.

Question: What are the MDS (Metadata Services)?

Answer: Metadata Services (MDS) is a feature provided by oracle to store customization and personalization information in a repository. The repository can either be stored in a database or in a file system as we will see.

For example if a screen has a table, this table has 8 columns, and there are a user (User1) want to see only 4 columns and hide the others. When User1 login again he want to see last changes which he make (see only 4 columns), the user can see any changes he make in the screen only if you apply MDS to your application.