Java Server Pages

Developing Generic Database Custom Actions

The database custom actions introduced in Chapter 9 can be used like this in a JSP page:

<ora:sqlTransaction dataSource="example">

  <ora:sqlUpdate>
    UPDATE Account SET Balance = Balance - ?
      WHERE AccountNumber = ?
    <ora:floatValue param="amount" />
    <ora:intValue param="account" />
  </ora:sqlUpdate>
  <ora:sqlUpdate>
    UPDATE Account SET Balance = Balance + ?
      WHERE AccountNumber = ?
    <ora:floatValue param="amount" />
    <ora:intValue param="account" />
  </ora:sqlUpdate>

</ora:sqlTransaction>

The database custom actions use all of the classes described previously in this chapter. A DataSource available in the application scope is used to get a Connection, and an SQLCommandBean is used to execute the SQL statement specified in the database action element body. The nested value actions create Value subclass instances and add them to a list held by the parent action tag handler. The <ora:sqlQuery> action saves the result as a Vector of Row objects in the scope specified by the page author. In this section, we first look at how the tag handlers for the <ora:sqlQuery>, <ora:sqlUpdate>, and <ora:sqlIntValue> actions are implemented. All value actions follow the same pattern as <ora:sqlIntValue>, so they are not described here. At the end of this section, we also look at the tag handler for the <ora:sqlTransatction> action to see how it provides a transaction scope for the database actions nested in its body.

The <ora:sqlQuery> and <ora:sqlUpdate> Actions

The ...