JavaServer Pages, 3rd Edition

Accessing Context Information

As you have seen in the previous chapters, a custom action element in a JSP page consists of a start tag (possibly with attributes), optionally a body, and an end tag:

<prefix:actionName attr1="value1" attr2="value2">
  The body
</prefix:actionName>

If the action element doesn’t have a body, the following shorthand notation can be used instead:

<prefix:actionName attr1="value1" attr2="value2" />

A tag handler implements the custom action’s behavior. When the container encounters a custom action, it creates an instance of the corresponding tag handler class, based on the information declared in the TLD.

In order for the tag handler to do anything interesting, it needs access to context information, such as the request and scope information, as well as the action element’s attribute values (if any). The container calls methods defined in the SimpleTag interface to provide this information. The container calls the setJspContext( ) method to provide the context information in the form of a JspContext instance. For the attribute values, the JSP container treats the tag handler as a bean and calls a setter method for each attribute. When the tag handler has been initialized, the container asks it to do its thing by calling the doTag( ) method, as shown in Figure 21-1.

Figure 21-1. SimpleTag interface methods and property setter methods

Here are the SimpleTag