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Processing the Withdrawal

In the last section of this tutorial, you created some variables to hold the session bean's state, and implemented an SQL query that used information from a database to fill in the state information. Now that you have the necessary information in the bean, you can define behaviors that process the data in various ways.

For this exercise, you will create a simple implementation of a transaction that represents a bank withdrawal. The capsule needs to update both the information it holds in its variables, and the information that should change in the database as a result of the withdrawal. AppComposer's SQLUpdate actor allows you to modify information in a database, just as the SQLSelect actor allowed you to retrieve information from the database. Finally, you will implement some methods that allow capsules or programs outside of the bean to access the state information it holds.

You can summarize the steps for building this part of the capsule as follows:

  1. Updating the variables that hold the bean's state.
  2. Configuring an SQL query to update the database with the new state.
  3. Implementing capsule methods and behaviors that allow outside programs to access the bean's state.

To implement the withdraw method:

  1. Create a new method on the capsule called withdraw.
    1. Select the capsule in the outline.
    2. Click the icon next to Methods in the Details pane.
    3. Set the activation to withdraw.
    4. Set Transaction Level to Required.
    5. Add an argument called amount of type double.
    6. Click OK.
    Since this method needs to commit information to a database, it should require a transaction when it executes.
  2. Insert an action group as a child of the capsule and name it withdraw. Set it to activate when it receives the withdraw method from the capsule.
  3. You need to update the balance data item that holds the current account balance. Insert an action behavior as a child of the withdraw group and name it setBalance. This behaivor updates the balance variable of the bean. The Eval field subtracts the amount parameter from the value in balance, and sets that as the new value for balance. Recall that the capsule method you defined includes an argument called amount. This represents the amount of the withdrawal.

    Notice that this behavior does not include error checking. Real beans should always include this. For instance, you should be check to ensure that the withdrawal amount is not more than the current balance.

So far you have a very simple implementation of a method to process a withdrawal from an account and save the new state in the bean. Later you will add some more behaviors to the withdraw group that update the information in the database. Before you do that, you need to configure the SQLUpdate actor, which determines what information in the database to change.

To configure the SQLUpdate actor:

  1. Add a SQLUpdate actor to the capsule and name it balanceUpdate.
  2. Click the Edit button in the details pane.
  3. In the Table tab, choose the ejbdata connection and ACCOUNTS table as you did for the SQLSelect actor.
  4. In the Columns tab, update the BALANCE column with a parameter (also) named BALANCE. The capsule feeds the query the value of this parameter when the balanceUpdate actor executes.
  5. In the Conditions tab, have it check that the column ACCOUNT_NUMBER equals the value of the parameter called ACCOUNTNUM. This tells the actor which account to update.
  6. Click OK.

Now that you have configured the update actor, you need to tell it when to execute, and provide it with the parameters it needs to update the database. Add some behaviors to the the withdraw action group so that it updates the account in the database with the new balance.

To update the information in the database:

  1. As a child of the withdraw group, add an action and name it setBalanceParm. Configure this so that it sets the balance parameter of the SQLUpdate actor. Since you already calculated the new value of the capsule's balance variable, use that to assign value to the SQLUpdate parameter with the same name. Make sure that this behavior comes after the setBalance behavior in the action group. When two behaviors activate on the same event, as these two do, the capsule processes them in the order they appear in the outline.
  2. As another child of withdraw, add an action behavior called setAccountParm. Configure this behavior to send the accountNumber parameter that the bean received with the create method to balanceUpdate's accountNum variable.
  3. Create an action to execute the database update. Name it execute update and edit it so it sends a message of execute to balanceUpdate.

You have now implemented all of the business methods that use SQL. Your capsule outline should look like this:

Sending out the Results

The session bean capsule needs two final business methods to be useful. Beyond just updating the information in the bean and database, a client should be able to request the current balance. The SimpleBank application needs to display the customer's name and the balance of their account on a web page. The next two behaviors you build access the state of the bean and do not change information in the database. An outside capsule will act as a client and use these methods through the finished session bean.

To retrieve the name:

  1. Create a new capsule method called getName that returns a String. Leave the transactional attribute to the default, which is Supports. This method does not need arguments.
  2. Insert a return value behavior as a child of the capsule and name it returnName.
  3. The method should return the name variable when a client calls the getName method.

To retrieve the balance:

To implement the getBalance business method on the capsule, you need a behavior that retrieves the balance value that was set in the ejbCreate method.

  1. Create a new capsule method called getBalance that returns a double. Leave the transactional attribute to the default, which is Supports.
  2. Insert a return value behavior as a child of the capsule and name it returnBalance.
  3. Set the behavior to return the balance attribute when the client calls the getBalance method.

If you are familiar with EJBs, you may be interested in what the source code of your bean looks like at this point. Select Source from the Capsule menu. You see the implementation of the getBalance and getName methods in the bean implementation and in the remote interface. Notice that the methods in the remote interface throw a RemoteException, as required by the EJB specification.

You have built a functionally complete session bean capsule. It can get information from and update a database, and send that information out on request. At this point, your capsule outline should look like this:

You are ready to generate, deploy and use you session bean. The next section of the tutorial shows you how to finish off and test your session bean capsule.

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