JavaServer Pages, 3rd Edition

Setting Action Attribute Values

Let’s talk about the “Java type” and “Dynamic value accepted” column values in Table 7-1. The category attribute value for the <ora:motd> action has the value String in the “Java type” column. String is the Java type for a text value. Action attributes can be of any Java type, the same as the bean properties discussed in Chapter 6. Say, for instance, that the <ora:motd> action had another attribute for setting the number of messages to return. It would make sense for this attribute to be of type int (a whole number). The container treats attribute values the same as bean properties and automatically converts text values to numeric and Boolean values, using the same conversion methods, so this attribute could still be set as a text value. The same as for a bean, a Java programmer can also link a property editor to a custom action to convert text values to more complex data structures.

A custom action attribute may also accept an EL expression as well as a static text value. An EL expression is evaluated for each page request, so it allows you to provide an attribute value that differs between invocations. The value in the “Dynamic Value Accepted” column tells if the attribute can be set by an EL expression. As you can see in Table 7-1, the category attribute for the <ora:motd> action does accept an EL expression. Support for EL expressions isn’t a given, but typically all attributes except those named var and scope accept an EL expression value (a ...